principles of heredity: variation in corn -...

Lesson A4–2

PRINCIPLES OF HEREDITY:VARIATION IN CORN

Unit A. Plant Science

Problem Area 4. Managing Inputs for Plant Growth

Advanced Life Science Area: Plants and Soils

Standard PS.4.5 Plant Genetics—Chemistry and Expression: Describe a situa-tion in which a plant characteristic is controlled by many genes.

Standard PS.5.1 Evolutionary Trends and Ecology: Explain the significance ofgenetic diversity to evolution. Explain how both meiosis and fertilization contribute to diversitywithin a gene pool. Describe how outcrossing promotes diversity, and ways that plants preventself-pollination and/or promote cross-pollination. Discuss how genetic diversity is preservedamong both crops and wild plants. List the assumptions of the Hardy-Weinberg Principle.Explain the disadvantages of lack of diversity in the wild and monoculture in the field.

Standard PS.5.2 Evolutionary Trends and Ecology: Compare and contrast natu-ral selection with artificial selection, as used by humans to domesticate plants and breedimproved varieties. Describe some of the traits that have been selected in the domestication ofplants. Contrast the rates at which gene frequencies change during natural selection, artificialselection involving traditional breeding, and breeding programs involving biotechnology.

Standard PS.5.5 Evolutionary Trends and Ecology: Define hybridization, anddescribe how it can lead to the development of unique species and varieties.

Standard PS.5.6 Evolutionary Trends and Ecology: Describe methods of produc-ing transgenic plants and ways in which they are used. Describe some of the risks of conventionaland biotech plant breeding. Explain that the risks and benefits of introducing a gene depend onthe identity of the gene rather than the mechanism by which it is introduced. Discuss the risksand benefits of several genes that have been introduced into plants by genetic engineering.

Biological Science Applications in Agriculture Lesson A4–2 •

Student Learning Objectives. Instruction in this lesson should result in stu-dents achieving the following objectives:

1 Explain other types of relationships between alleles and how to determine the

probable outcome of these relationships.

2 Explain how to determine the genotype of an unknown individual.

3 Demonstrate how the probability is determined for dihibrid crosses.

4 List four examples of mutations and explain how mutations can change the genetic

make-up of an organism.

5 Explain how humans have manipulated the genetic make-up of organisms.

List of Resources. The following resources may be useful in teaching this lesson:

AgriScience Lesson Plan Library—Unit C. Basic Principles of Agricultural/Horticul-tural Science—Problem Area 3. Understanding Cells, Genetics, and Repro-duction—Lesson 4. Understanding Crossbreeding and Hybrids. Danville, IL:CAERT, Inc.

Kemper, Dave, et al. Writer’s Inc. Wilmington, Massachusetts: Write Source,Houghton Mifflin Company, 2001.

Miller, Dr. Kenneth R. and Dr. Joseph Levine. Biology. Prentice Hall—PearsonEducation, Inc. Upper Saddle River, New Jersey, 2002.

Osborne, Edward W. Biological Science Applications in Agriculture. Danville, IL: Inter-state Publishers, Inc., 1994.

Towle, Albert. Modern Biology. Austin: Holt, Rinehart and Winston, 2003.

List of Equipment, Tools, Supplies, and Facilities

� Writing surface

� Overhead projector

� Transparencies from attached masters

� Copies of student lab sheets

Terms. The following terms are presented in this lesson (shown in bold italics):

� albinism

� chromosome mutation

� codominance

� deletion


� dihybrid cross

� diploids

� frameshift mutation

� gene mutation

� haploids

� heterosis

� hybridization

� hybrid vigor

� incomplete dominance

� inversion

� lethal mutation

� multiple alleles

� mutation

� nondisjunction

� point mutation

� polygenic traits

� polyploidy

� selection

� testcross

� tissue culture

� transgenic plant

� translocation

Interest Approach. Use an interest approach that will prepare the students for thelesson. Teachers often develop approaches for their unique class and student situations. A possi-ble approach is included here.

Bring in several different plants for students to view. Question them as to why the

plants look the way they do. If possible bring in a plant and its parents (or pretend)

and quiz them on the differences and why there are differences.

Invite a representative from a seed company to speak to the class about the use of

progeny information in making plant breeding decisions to develop new varieties of

seed.


SUMMARY OF CONTENT AND

TEACHING STRATEGIES

Objective 1: Explain other types of relationships between alleles and how to determinethe probable outcome of these relationships.

Anticipated Problem: What are other types of relationships between alleles and how do wedetermine the probable outcome of these relationships?

I. In genetics there are relatively few examples of complete dominance relationships amongalleles. There is a great degree of genetic variation between alleles.

A. Incomplete dominance is a relationship where the heterozygous individual will have aphenotype in between the parents. Japanese Four O’Clock flowers are an example ofincomplete dominance. In this type of a plant a homozygous dominant (RR) flower isred, a heterozygous (Rr) flower is pink, and a homozygous recessive (rr) flower is white.

B. Codominance is when a heterozygous offspring will express both alleles for a gene. Forexample, roan coat color in shorthorn cattle and in horses is where the animals have redhairs and white hairs present in their coat. The following letters are used to representthese alleles: RR = red, RR’ = roan; and R’R’ = white.

C. Of course not all traits are a matter of simple dominance or recessiveness. Many traitssuch as the number of fruit, size of the fruit, size of the plant, and overall yield areaffected by many different genes. Polygenic Traits are those that are governed by morethan one gene. The phenotype that is observed is a result of all the genotypes for thattrait that are present.

D. Multiple alleles are genes that have more than two different alleles that trait. For exam-ple, blood types in humans have three different alleles—IA, IB, and i. These three allelesform six different genotypes. Coat color in rabbits and human eye color are also exam-ples of multiple allele traits.

Use TM–A to illustrate genetic variation. Conduct LS–B on Human Characteristics;

this will help students understand how much variation as well as similarity that exists

between individuals within a species.


Objective 2: Explain how to determine the genotype of an unknown individual.

Anticipated Problem: How is the genotype of an unknown individual determined?

II. A testcross is a procedure that scientists use to determine the genotype of an unknown indi-vidual. If an organism possesses the dominant phenotype, they do not know if it is homozy-gous dominant or heterozygous. In order to determine the unknown genotype, they crossthe unknown with a homozygous recessive.

A. For example, a purple flowered pea plant could be PP (homozygous dominant) or het-erozygous (Pp). The purple flowered plant is crossed with a white flowered plant (pp)to determine the genotype of the first pea plant.1. If 100% of the offspring have purple flowers, then the unknown is homozygous

dominant or PP. If half of the offspring have purple flowers and half have whiteflowers, then the unknown is heterozygous or Pp.

2. If the unknown is crossed with anything other than a homozygous recessive, theresults could be inconclusive. An unknown purple flowered pea plant crossed withanother purple flowered pea plant could result in offspring that all have purple flow-ers, but that does not guarantee that they both are homozygous dominant.

B. Test crosses are performed in parent seed research departments to ensure that plants arepure for particular traits. Only pure strains can be used to develop hybrid crops.

Use TM–B to review the definition of a testcross. Reinforce the concepts presented in

the first two objectives by assigning LS–C. Quiz student understanding with LS–E.

Objective 3: Demonstrate how the probability is determined for dihibrid crosses.

Anticipated Problem: How is the probability determined when considering two differentsets of traits?

III. A dihybrid cross is one where two different sets of traits are considered. For example, roundversus wrinkled seeds and yellow versus green seeds in peas. In this case a 16 square punnettsquare is used. Each trait is distributed independently of the other. After determining thegenotype of the parents, then determine all of the possible combinations of the two traitsthat are to be combined.

Use TM–C to illustrate a dihybrid cross. Assign LS–D to reinforce student understand-

ing of this objective. Quiz student comprehension with LS–F.


Objective 4: List four examples of mutations and explain how mutations can changethe genetic make-up of an organism.

Anticipated Problem: What is a mutation and how does can it change the genetic code of anorganism?

IV. Selection is the process of breeding plants that are selected for a particular characteristic.This leads to the dominance of certain genetic traits. Producers can select the traits that theywant and may select for traits that are a result of a mutation. A mutation is when the DNA ischanged or varies in an organism. This results in the development of a new trait that did notexist in the parents. Natural mutations have been found in the “Gala” apple resulting in newvarieties called “Royal Gala” and “Imperial Gala.” Mutations cannot be predicted and thereare several types of mutations.

A. There are a number of different types of mutations.

1. Gene mutations involve changes in the gene and not in the entire chromosome.a. Point mutations involve the substitution of one nucleotide for another nucleo-

tide on the DNA molecule. For example, GTATCC becomes GGATCC.b. Frameshift mutations result from either the insertion or deletion of a nucleotide

in the DNA sequence. Because DNA is read as a series of condons (a sequenceof three nucleotides), this changes the DNA sequence from that point forward.For example, GTATCC becomes GTTATC or GATCC.

2. Examples of chromosome mutations include deletion, inversion, translocation, andnondisjunction.a. Deletion is when a piece of a chromosome breaks off losing part of the genetic

information.b. Inversion is when a piece of the chromosome breaks off and reattaches itself to

the same chromosome.c. Translocation is when a piece of a chromosome breaks off and reattaches itself to

a different chromosome.d. Nondisjunction is when a chromosome does not separate from its homologue

(one of a pair of chromosomes—i.e.—humans have two #1 chromosomes, etc.)during meiosis. This results in one gamete receiving two copies of the chromo-some and the other receiving none of this particular chromosome. In humans,Down Syndrome is a result of the offspring receiving three copies of chromo-some 21 and Turner’s Syndrome is a result of the offspring receiving only onesex (number 23) chromosome.

B. When a mutation occurs in a gamete (egg or sperm), it is referred to as a germ-cell muta-tion. When this occurs, the mutation can be passed on to the offspring.

C. When non-reproductive cells experience a mutation, the change will only affect thatorganism; it cannot be passed on their offspring.

D. Lethal mutations result in death. A plant or part of a plant lacking chlorophyll is called analbino. Albinism is usually lethal in higher plants.


E. Some mutations are beneficial and result in the change of a species causing evolution tooccur. One example of a beneficial mutation can be found in Hereford cattle. The allelefor polled is dominant and is a result of a mutation that resulted when horned Herefordswere crossed.

F. Mutations can be caused by radiation (x-ray or nuclear), chemicals, environment, or byaccident.

Use TM–D to review the concepts involved in mutation.

Objective 5: Explain how humans have manipulated the genetic make-up of organ-isms.

Anticipated Problem: How have humans changed or manipulated the genetic make-up oforganisms?

V. Because selection requires a great deal of time to produce new offspring and the environ-ment can affect the outcome, several techniques have been developed to maximize produc-tion. Researchers can use a variety of breeding techniques to manipulate and select for avariety of beneficial traits.

A. Hybridization is the breeding of two pure lines resulting in offspring that possess thebest characteristics of the two parent strains. Hybridization has been used for the pastcentury and results in hybrid vigor. Examples of hybrid vigor or heterosis include fastergrowth, greater vigor, increased disease resistance, and other beneficial characteristics.Hybrid seed corn is probably the most visible example of hybridization. If the offspringof a hybrid cross are allowed to reproduce, the hybrid vigor will probably be lost.

B. Tissue culture is a method used by plant researchers to produce a large number of off-spring by using a few cells from the parent. A small slice of cells (explant) is cut off of theparent, placed in a growing medium that contains proper nutrients and hormones, andthe cells develop into an entirely new plant. The new plant is a clone of the parent. Thisis beneficial for creating a large number of plants in a short amount of time when theplant is unique in nature. For example, a blue rose was developed through years ofresearch. Using tissue culture allowed the blue rose to be mass produced rather thantrying to use traditional breeding techniques which would require an enormousamount of time.

C. A transgenic plant is one that has been produced through the process of genetic engi-neering. Genetic engineering takes DNA from one organism and inserts it into theDNA or another organism. Canola is an example of a transgenic plant. A variety ofcanola contains DNA from a flounder which allows the canola to be grown in colderregions stretching the growing season an additional month. Other plants have beenmodified to include genes to resist certain diseases or microorganisms.

D. Plants can frequently have more than two sets of chromosomes in their cells. This hap-pens in nature and can also be induced by man.


1. Haploids are cells that contain one copy of each chromosome in the nucleus. Theegg and sperm cells are haploid cells. This is referred to as 1n where n represents thenumber of different chromosomes.

2. Diploid cells are ones that contain two copies of each chromosome in the nucleus.In animals all cells except the sex cells are diploids. Animals that possess more or lessthan the diploid number of chromosomes are considered mutations. This isreferred to as 2n.

3. However, it is very common in plants for them to have more than two copies of eachchromosome. This is referred to as polyploidy. Over 1/3 of plant species are esti-mated to be polyploidy.a. Corn and cultivated barley are examples of diploid agronomic crops. Apples and

bananas can be either 2n or 3n. Alfalfa, potatoes, and cotton are tetraploid orhave four copies of each chromosome. Wheat is hexaploid; it has six copies ofeach chromosome. Strawberries contain 8 copies and boysenberries contain 7copies of each chromosome.

b. Polyploidy can be caused by nondisjunction during meiosis (the chromosomesdid not separate during cellular division) or by artificial means. Scientists havelearned that the application of colchicine which comes from the root of theAutumn crocus can be applied to seeds or seedlings to cause the doubling ofchromosomes. Irradiation and chemicals can also cause polyploidy. Polyploidyhas been created in snapdragons, marigolds, and watermelon.

c. Polyploidy can be valuable in plant production. Some plants will experience anincrease in cell size and an increase in the size of the fruit. Some plants will besterile or have a difficult time reproducing and an increased rate of death canresult. Seedless grapes, citrus, and watermelon are examples of triploid plants.

d. This characteristic makes it hard to study the genetics of plants.

Use TM–E to illustrate genetics and technology. Conduct the experiment on genetic

variation (LS–A). Test student understanding using the test in this lesson. Use the fol-

lowing resource to further develop students’ understanding of hybridization:

AgriScience Lesson Plan Library—Unit C. Basic Principles of Agricultural/Horticultural

Science—Problem Area 3. Understanding Cells, Genetics, and Reproduction—Lesson

4. Understanding Crossbreeding and Hybrids. Contact your local seed dealer. Have

them visit with the class to talk about the seed research industry and how it works.

Make sure to ask about education and employment experience necessary for the dif-

ferent types of jobs. Tie the different aspects of seed production to science and

emphasize how genetic understanding is making increased yields and disease resis-

tance possible. Visit Monsanto’s Research Center in Chesterfield, Missouri for a first

hand look at research; this must be arranged locally (i.e.—fertilizer company).

Review/Summary. Focus the review and summary of the lesson around the studentlearning objectives. Call on students to explain the content of each objective.


Application. Application can involve one of the following student activities using theattached transparency masters and lab sheets:

� TM–A: Genetic Variation� TM–B: Testcross� TM–C: Dihybrid Cross� TM–D: Mutation� TM–E: Genetics and Technology� LS–A: Principles of Heredity: Genetic Variation in Corn� LS–B: Inheritance in Humans� LS–C: Genetic Variation Review #2� LS–D: Genetic Variation Review #3� LS–E: Genetic Variation Quiz #2� LS–F: Genetic Variation Quiz #3� TS–A: Principle of Heredity: Variation in Corn

Evaluation. Evaluation should concentrate on student achievement of the lesson’sobjectives. A sample test is included.

Answers to Sample Test:

Part One: Matching

1. d2. f3. h4. g5. a6. c7. e8. b

Part Two: Fill-in-the-blank

1. lethal2. tissue culture3. hybridization4. diploid

Part Three: Multiple Choice

1. b2. d


3. a4. c5. a6. d

Part Four: Short Answer

1. Answers will vary.2.

R R

R RR RR

r Rr Rr

Genotypes—2/4 RR, 2/4 RrPhenotypes—2/4 red, 2/4 pink

3.

gR gR gR gR

GR GgRR GgRR GgRR GgRR

Gr GgRr GgRr GgRr GgRr

gR ggRR ggRR ggRR ggRR

gr ggRr ggRr ggRr ggRr

Genotypes—4/16 GgRR, 4/16 GgRr, 4/16 ggRR, 4/16 ggRrPhenotypes—8/16 yellow and smooth, 8/16 green and smooth


4. The purpose of a testcross is to determine the genotype of an unknown.5.

a. Considering the first scenario—a homozygous yellow pea seed plant is crossed withthe green seed pea plant.

G G

g Gg Gg

g Gg Gg

Genotypes—4/4 GgPhenotypes—4/4 yellow seeded pea plants

b. Considering the second scenario—a heterozygous plant is crossed with the homo-zygous recessive.

G g

g Gg gg

g Gg gg

Genotypes—2/4 Gg, 2/4 ggPhenotypes—2/4 yellow, 2/4 green

c. If 100% of the offspring have yellow seeds, then the unknown is homozygous domi-nant or GG. If half of the offspring have yellow seeds and half have green seeds, thenthe unknown is heterozygous or Gg.

6. Haploid, diploid, and polyploid are all adjectives used to describe the number of eachchromosome that are present in a cell. Haploid means that there is only one copy, diploidis two copies, and polyploid is more than two copies of each chromosome in the cell.


Name ________________________________________Test


� Part One: Matching

Instructions: Match the word with the correct definition.

a. chromosome mutation d. mutation g. testcrossb. gene mutation e. polygenic traits h. transgenic plantc. haploid f. polyploidy

_______1. Results from the change in the DNA of an organism

_______2. Cells that contain more than two copies of each chromosome

_______3. A plant that has been created through man’s manipulation of the genetic information

_______4. A procedure used by scientists to determine the genotype of an unknown

_______5. Deletion, inversion, translocation, and nondisjunction are examples of this type of mutation

_______6. Cells that contain one copy of each chromosome

_______7. Traits that are governed by more than one gene

_______8. A mutation in the gene and not in the entire chromosome

� Part Two: Fill-in-the-Blank

Instructions: Complete the following statements.

1. ________________ is a change in the genetic code that results in death.

2. A method used by plant researchers to produce large quantities of cloned plants is called___________________.

3. The agriculture industry commonly uses _____________________ which is the breeding of two pure linesresulting in offspring that possess the best characteristics of both parents.

4. Cells that contain two copies of each chromosome are referred to as _________________.


� Part Three: Multiple Choice

Instructions: Circle the letter of the correct answer.

_______1. What type of mutation is the result of a piece of the chromosome breaking off and reattaching itselfto the same chromosome?

a. pointb. inversionc. nondisjunctiond. translocation

_______2. What type of mutation is the result of a piece of the chromosome breaking off and reattaching itselfto a different chromosome?

a. deletionb. inversionc. nondisjunctiond. translocation

_______3. What type of mutation is the result of a piece of the chromosome breaking off causing part of thegenetic information to be lost?

a. deletionb. inversionc. nondisjunctiond. translocation

_______4. What type of mutation is the result of the chromosomes not separating during meiosis causing thecell to not receive enough chromosomes or to receive too many chromosomes?

a. deletionb. inversionc. nondisjunctiond. frameshift

_______5. What type of mutation is the result of one nucleotide being substituted for another?

a. pointb. inversionc. frameshiftd. translocation

_______6. What type of mutation is the result of either the insertion or deletion of a nucleotide in the DNAsequence?

a. deletionb. pointc. nondisjunctiond. frameshift

� Part Four: Short Answer

Instructions: Answer the following questions.

1. Why is it important to study genetics?


2. Japanese 4 O’clock Flowers are an example of incomplete dominance. Cross a homozygous dominantplant with a heterozygous plant. Complete the Punnett Square, list each different genotype, list each dif-ferent phenotype, and list the ratios of each genotype and phenotype. Use a “R” to represent the domi-nant red color and “r” to represent the recessive white color.

3. Perform a dihybrid cross between two pea plants—ggRR × GgRr. Complete the Punnett Squares, list eachdifferent genotype, list each different phenotype, and list the probability of each genotype and pheno-type. Use the following alleles: G = yellow pea seeds, g = green pea seeds, R = smooth pea seeds, and r= wrinkled pea seeds.

4. What is the purpose of a testcross?

5. Assume that you have been contracted to grow garden pea seed for a local company. They are only inter-ested in purchasing yellow colored pea seeds for a niche market. Yellow pea seeds are completely domi-nant to green pea seeds. To insure the maximum amount of profit, you want to know that you are plant-ing seed that is pure for the yellow pea seed color. Show how to calculate a testcross—complete thePunnett Squares, list each different genotype, list each different phenotype, and list the probability ofeach genotype and phenotype. Explain how to determine the genotype of the unknown based on thephenotypes that could be produced.

6. Compare and contrast haploid, diploid, and polyploid.


TM–A

GENETIC VARIATION

Exotic items like these unusual maize specimens from

Latin America are preserved in the ARS National Plant

Germplasm System because they might have genes to

help solve future problems.

� Incomplete dominance is a relationship where the het-

erozygous individual will have a phenotype in between

the parents.

� Codominance is when a heterozygous offspring will

express both alleles for a gene.


(Courtesy, Agricultural Research Service, USDA)

TM–B

TESTCROSS

� Polygenic Traits—traits governed by more

than one gene

�Multiple alleles—genes that have more than

two different alleles that trait

� Testcross—a procedure that scientists use to

determine the genotype of an unknown indi-

vidual

� Purple flowered pea

� Homozygous purple plant is crossed with

the white plant.


TM–C

DIHYBRID CROSS

� Cross RrGg with RrGg—R = round, r = wrinkled, G =

yellow, g = green.

RG Rg rG rg

RG RRGG RRGg RrGG RrGg

Rg RRGg RRgg RrGg Rrgg

rG RrGG RrGg rrGG rrGg

rg RrGg Rrgg rrGg rrgg

� Genotypes—1/16 RRGG, 2/16 RRGg, 1/16 RRgg, 2/16 RrGG, 4/16 RrGg,2/16 Rrgg, 1/16 rrGG, 2/16 rrGg, 1/16 rrgg

� Phenotypes—9/16 round and yellow, 3/16 round and green, 3/16wrinkled and yellow, and 1/16 wrinkled and green

� Cross RRGg with RrGG—R = round, r = wrinkled, G =

yellow, g = green.

RG Rg RG Rg

RG RRGG RRGg RRGG RRGg

RG RRGG RRGg RRGG RRGg

rG RrGG RrGg RrGG RrGg

rG RrGG RrGg RrGG RrGg

� Genotypes—4/16 RRGG, 4/16 RRGg, 4/16 RrGG, 4/16 RrGg� Phenotypes—16/16 round and yellow


TM–D

MUTATION

�Mutation is when the DNA is changed in an

organism

� Different types of mutations include

� Gene mutations involve changes in the gene

and not in the entire chromosome

� Point mutations—substitution of one nucle-

otide for another nucleotide

� Frameshift mutations—insertion or deletion

of a nucleotide

� Chromosome mutations


TM–E

GENETICS AND TECHNOLOGY

Tubers of wild species

(right) are small and

otherwise unfit for the

table, but such plants

often have genes for

traits like high tuber

calcium that could

make important contri-

butions to the quality

of commercial cultivars

(left).

� Hybridization—the breeding of two pure lines resulting

in offspring that possess the best characteristics of the

two parent strains.

� Tissue culture—a method used to produce a large num-

ber of offspring by using a few cells from the parent.

� Transgenic plant—one that has been produced through

the process of genetic engineering.

� Chromosomes

� Haploids—one copy of each chromosome� Diploid—two copies of each chromosome� Polyploidy—more than two copies of each chromosome


(Courtesy, Agricultural Research Service, USDA)

LS–A: Teacher Information

PRINCIPLES OF HEREDITY:GENETIC VARIATION IN CORN

Research Problem

How are traits inherited from parents to offspring?

Agricultural Applications and Practices

The development of hybrid corn was a significant advancement in the effort to producemore food. Before hybrid seed was available, farmers saved their own seed each year.Now, practically all corn grown in the United States is a hybrid which has been developedfor a certain location and environmental condition. Hybrid corn varieties have boostedyields from 50–60 bushels per acre in the 1940’s to near 200 bushels per acre on manyfarms today.

Several botanical varieties of corn are grown in the United States and have broad usageand economic importance. The principal commercial feed type corn grown in the UnitedStates is dent com. White kernel corn is becoming increasingly popular as a specialty foodcrop for people. Sweet corn and popcorn are also important crops grown for human con-sumption. New varieties of corn developed through plant breeding programs and bio-technology are constantly being perfected at land-grant research institutions and by pri-vate industry.

Science Connections—Questions for Investigation

1. How are genes distributed into gametes and recombined into zygotes?

2. What is a dominant and recessive genes?

3. What is the most probable genotype for the ears that were evaluated? What is themost probable genotype of the parents of the ears that were evaluated?


Purpose of the Laboratory and Student Performance Objectives

The purpose of this laboratory exercise is to observe the result of genetic crosses in corn todetermine how genes arc distributed into gametes and zygotes. Through this experimentand related discussion, students will be able to:

1. Explain how traits are inherited from parents to offspring.

2. Predict probable results of single or multiple trait crosses.

Materials and/or Equipment

� 1 ear from a first generation cross between homozygous parents (can be purchasedfrom a science supply company)

� 1 ear from a second generation cross for two traits (can be purchased from a sciencesupply company)

Procedure

Give each group of students a copy of the worksheet to perform the activity.

Anticipated Findings

In “Genetic Variation” answers will vary for each ear of corn examined. The approximateratio of the expression of the dominant trait over the recessive trait will be 3:1.

Ideas for Additional Experiments.

Several variations of genetic corn are available from scientific supply companies and canbe used to demonstrate the properties of inheritance. Talk to your local science teachersfor more ideas.


Name:LS–A: Student Worksheet

PRINCIPLES OF HEREDITY:GENETIC VARIATION IN CORN

Procedure

1. Obtain an ear of genetic corn (first generation cross) and identify the varying trait ofinterest, (e.g. purple and white kernels)

2. Count and record the number of kernels of each color on the ear.

3. Calculate the ratio of expression for the traits being examined.

4. Obtain an ear of genetic corn from a second generation cross and identify the vary-ing traits of interest, (e.g. purple, white, starchy, and sweet kernels)

5. Count and record the number of kernels of each type and color on the ear.

6. Calculate the ratio of expression for the traits being examined.

7. Construct a table to record the kernel counts for your lab team as well as the resultsfrom all of your classmates. Calculate the class average.


LS–B: Teacher Information

INHERITANCE IN HUMANS

Research Problem

What characteristics in humans are dominant?

Agricultural Applications and Practices

Although man is an unfavorable object for genetic study, the study of human inheritanceis an important and interesting topic. By gaining a better understanding of how humangenetics works we can gain a better understanding of how the organisms around us func-tion and how we can exert a positive influence on the environment around us. TheHuman Genome Project has helped scientists and society to have a much greater under-standing of the world around us. Dozens of gene-controlled characters have been studiedand their inheritance explained.

Science Connections—Questions for Investigation

1. What traits do you have that are examples of dominant traits? Recessive?

2. What traits do you have that are examples of incomplete dominance?

3. Compare your phenotypes with those of your classmates. How similar are you toyour classmates? Explain.

4. Which traits do you possess that make you unique?

5. Explain how traits are passed from parents to offspring. Be specific.

6. Using the Internet or newspaper, learn more about the Human Genome Projectand the latest advancements that have been made. Explain in one well written para-graph how the Human Genome Project has helped us and could further help us insolving the mystery of genetic.

Purpose of the Laboratory and Student Performance Objectives

The objective of this lab activity is to introduce you to some characteristics of humans andhow they may be transmitted from parents to offspring. Through this experiment andrelated discussion, students will be able to:

1. Explain how traits are inherited from parents to offspring.


2. Give examples of human genetic traits that are dominant, recessive, or incompletedominance.

Materials and/or Equipment

� PTC taste paper (can be purchased from a science supply company for a very nominalamount)

� Untreated taste paper (can be purchased from a science supply company for a verynominal amount)

Procedure

Give each group of students a copy of the worksheet to perform the activity.

Anticipated Findings

Answers will vary. Be cautious of students that may feel uncomfortable in discussing theirfamily’s genetic characteristics.


Name ________________________________________LS–B: Student Worksheet

INHERITANCE IN HUMANS

Procedure

1. Read through the procedure. Working with your lab team, determine how the datawill be collected.

2. With the help of your lab team determine your genotype and phenotype for the fol-lowing traits.

a. Attached ear lobes—In most people the ear lobes hang free (E), but in individu-als homozygous for the recessive gene (e), the bottoms of the ear lobes areattached directly to the side of the head. There is variation in the size and appear-ance of ear lobes and other genes can modify the expression of this trait.

b. PTC Taster—Place a strip of untreated taste paper in your mouth and note howit tastes. Next, place a strip of PTC paper in your mouth and note the taste. If youcan taste the bitter PTC paper, then you possess the dominant (T) allele. If youcannot taste the bitter PTC paper, then you are homozygous recessive.

c. Tongue rolling—A dominant gene (R) gives some people the ability to roll theirtongue into a U-shape when extending the tongue from the mouth. Thisinvolves curling the sides of the tongue upward. People who do not possess thisgene can only produce a slight downward curve of the tongue when it isextended from the mouth and are homozygous recessive.

d. Hairline—Individuals with a straight hairline across the front of their head arehomozygous recessive or ww. If a widow’s peak is exhibited or a downwardpoint at the center of the hairline, then they possess the dominant gene for thistrait (W).

e. Long palmar muscle—Individuals homozygous for a recessive gene (l) have along palmar muscle that can be detached by inspection of the tendons on theinside of the wrists. To view this clench your fist tightly and flex your hand.Now observe the tendons. If there are three, then a long palmar muscle is pres-ent. If there are only two (the large middle one will be missing), then this muscle


is absent. Because of the variation in gene expression, this middle tendon is pres-ent sometimes in one wrist, but not both. If you find it in either wrist, then youare homozygous recessive (ll). If it is not present in either wrist, then you havethe dominant gene (L).

f. Interlocking fingers—When clasping the hands (fingers interlocked), some peo-ple usually place the left thumb on top of the right while others place the rightover the left. When you do the opposite you will probably feel awkward. Scien-tists believe that placing the left thumb over the right is due to the recessive con-dition, ff.

g. Thumb—A hitchhiker’s thumb or one where the end bends back at least 30degrees in a dominant trait (BB or Bb). A straight thumb is recessive or bb.

h. Mid-digital hair—Some people have hair on the middle (second) section of thefingers. The absence of hair on all fingers is due to a recessive gene (m). Thepresence of hair is due to a dominant allele (M). A number of alleles can deter-mine if the hair shall grow on one or more of the fingers. Since this hair may bevery fine look very closely.

i. Second finger shorter than the fourth—The length of the index (second) fingerin relation to the ring (fourth) finger is an inherited characteristic that appears tobe influenced by gender. Place your hand palm down on a sheet of ruled note-book paper. Determine which finger is longer. It is believed that the shorterindex finger results from the action of a sex-influenced gene which is not thesame as a sex-linked gene. The shorter index finger is recessive in the female anddominant in the male. Use (SS) for the short second finger and the symbol (SL)in instances where the index finger is longer, or as long as the fourth finger.These should also be grouped according to gender since the frequency shouldvary.

j. Hair Texture is an example of incomplete dominance. Is your hair straight,wavy, or curly? Curly hair is HH (homozygous dominant), wavy hair is Hh(heterozygous), and straight hair is hh (homozygous recessive).

k. Lip protrusion is another example of incomplete dominance. Incomplete domi-nance is exhibited by protruding lips (PP). Nonprotruding lips are homozygousrecessive (pp) and slightly protruding lips are heterozygous (Pp).

l. Inter-eye distance is also an example of incomplete dominance. If the eyes arespaced far apart are dd, eyes spaced closely are DD, and medium spaced eyes areDd.

**Caution—some of these traits can also be influenced by the environment.

3. Design a data table to record the information. Collect the observations of the entireclass and enter the data in your table.


Inheritance in Humans Data Table

Characteristic Your PhenotypeYour PossibleGenotype(s)

# Classmateswith Dominant

Phenotype

# Classmateswith Recessive

Phenotype

Attached ear lobes

PTC Taster

Tongue Rolling

Hairline

Long Palmar Muscle

Interlocking Fingers

Thumb

Mid-digital Hair

Second/Fourth Finger

Hair Texture

Lip Protrusion

Inter-Eye Distance

Extra Credit

Collect and record data on at least three of the characteristics that are discussed in thishandout, construct a pedigree chart for one characteristic, and interpret briefly the modeof inheritance as exhibited by your family. If possible, use your parents, any brothers andsisters, and your grandparents.


LS–C: Teacher Information

GENETIC VARIATION REVIEW #2—22 POINTS

Answers

1. The purpose of a testcross is to determine the genotype of an unknown.

2. Considering the first scenario—a homozygous black male is crossed with homozy-gous recessive female.

B B

b Bb Bb

b Bb Bb

Genotypes—4/4 Bb

Phenotypes—4/4 black guinea pigs

a. Considering the second scenario—a heterozygous plant is crossed with thehomozygous recessive.

B b

b Bb bb

b Bb bb

Genotypes—2/4 Bb, 2/4 bb

Phenotypes—2/4 black, 2/4 brown


b. If 100% of the offspring are black, then the unknown is homozygous dominantor BB. If half of the offspring black and half are brown, then the unknown is het-erozygous or Bb.

3.

r r

R Rr Rr

r rr rr

Genotypes—2/4 Rr, 2/4 rr

Phenotypes—2/4 pink, 2/4 white

4.

R R’

R’ RR’ R’R’

R’ RR’ R’R’

Genotypes—2/4 RR’, 2/4 R’R’

Phenotypes—2/4 roan, 2/4 white


Name ________________________________________LS–C: Student Worksheet



2. Assume that you are raising guinea pigs for a local pet store. They are only interestedin purchasing black coat colored animals. You are interested in buying a black malefrom a friend, but are unsure of the genotype of the guinea pig. Show how to calcu-late a testcross—complete the Punnett Squares, list each different genotype, list eachdifferent phenotype, and list the ratios of each genotype and phenotype. Explainhow to determine the genotype of the unknown animal based on the phenotypesthat could be produced.


3. Japanese 4 O’clock Flowers are an example of incomplete dominance. Cross ahomozygous recessive male with a heterozygous female. Complete the PunnettSquare, list each different genotype, list each different phenotype, and list the ratiosof each genotype and phenotype. Use a “R” to represent the dominant red color and“r” to represent the recessive white color.

4. Roan hair color in horses is an example of codominance. Cross a heterozygous malewith a homozygous recessive female. Complete the Punnett Square, list each differ-ent genotype, list each different phenotype, and list the ratios of each genotype andphenotype. Use a “RR” to represent a red coat color and a “R’R’” to represent awhite coat color.


LS–D: Teacher Information


Answers

1.

GR Gr GR Gr

gR GgRR GgRr GgRR GgRr

gr GgRr Ggrr GgRr Ggrr

gR GgRR GgRr GgRR GgRr

gr GgRr Ggrr GgRr Ggrr

Genotypes—4/16 GgRR, 8/16 GgRr, 4/16 Ggrr

Phenotypes—12/16 yellow and smooth, 4/16 yellow and wrinkled

2.

GR Gr gR gr

GR GGRR GGR GgRR GgRr

Gr GGRr GGrr GgRr Ggrr

gR GgRR GgRr ggRR ggRr

gr GgRr Ggrr ggRr ggrr

Genotypes—1/16 GGRR, 2/16 GGRr, 1/16 GGrr, 2/16 GgRR, 4/16 GgRr, 2/16Ggrr, 1/16 ggRR, 2/16 ggRr, 1/16 ggrr

Phenotypes—9/16 yellow and smooth, 3/16 yellow and wrinkled, 3/16 green andsmooth, 1/16 green and wrinkled


Name ________________________________________LS–D: Student Worksheet


1. Perform a dihybrid cross between two pea plants—GGRr × ggRr. Complete thePunnett Squares, list each different genotype, list each different phenotype, and listthe probability of each genotype and phenotype. Use the following alleles: G = yel-low pea seeds, g = green pea seeds, R = smooth pea seeds, and r = wrinkled peaseeds.

2. Perform a dihybrid cross between two pea plants—GgRr × GgRr. Complete thePunnett Squares, list each different genotype, list each different phenotype, and listthe probability of each genotype and phenotype. Use the following alleles: G = yel-low pea seeds, g = green pea seeds, R = smooth pea seeds, and r = wrinkled peaseeds.


LS–E: Teacher Information

GENETIC VARIATION QUIZ #2—22 POINTS

Answers

1. The purpose of a testcross is to determine the genotype of an unknown.

2. Considering the first scenario—a homozygous black male is crossed with homozy-gous recessive female.

B B

b Bb Bb

b Bb Bb

Genotypes—4/4 Bb

Phenotypes—4/4 black guinea pigs

a. Considering the second scenario—a heterozygous plant is crossed with thehomozygous recessive.

B b

b Bb bb

b Bb bb

Genotypes—2/4 Bb, 2/4 bb

Phenotypes—2/4 black, 2/4 brown


b. If 100% of the offspring are black, then the unknown is homozygous dominantor BB. If half of the offspring black and half are brown, then the unknown is het-erozygous or Bb.

3.

R r

R RR Rr

r Rr rr

Genotypes—1/4 RR, 2/4 Rr, 1/4 rr

Phenotypes—1/4 Red, 2/4 pink, ¼ white

4.

R’ R’

R RR’ RR’

R’ R’R’ R’R’

Genotypes—2/4 RR’, 2/4 R’R’

Phenotypes—2/4 roan, 2/4 white


Name ________________________________________LS–E: Student Worksheet



2. Assume that you are raising satin rabbits for a local pet store. They are only inter-ested in purchasing black coat colored animals. You are interested in buying a blackmale from a friend, but are unsure of the genotype of the rabbit. Show how to calcu-late a testcross—complete the Punnett Squares, list each different genotype, list eachdifferent phenotype, and list the ratios of each genotype and phenotype. Explainhow to determine the genotype of the unknown animal based on the phenotypesthat could be produced.


3. Japanese 4 O’clock Flowers are an example of incomplete dominance. Cross a het-erozygous male with a heterozygous female. Complete the Punnett Square, list eachdifferent genotype, list each different phenotype, and list the ratios of each genotypeand phenotype. Use a “R” to represent the dominant red color and “r” to representthe recessive white color.

4. Roan hair color in Shorthorn cattle is an example of codominance. Cross a homozy-gous recessive male with a heterozygous female. Complete the Punnett Square, listeach different genotype, list each different phenotype, and list the ratios of eachgenotype and phenotype. Use a “RR” to represent a red coat color and a “R’R’” torepresent a white coat color.


LS–F: Teacher Information


Answers

1.

Dr Dr dr dr

dR DdRr DdRr ddRr ddRr

dr Ddrr Ddrr ddrr ddrr

dR DdRr DdRr ddRr ddRr

dr Ddrr Ddrr ddrr ddrr

Genotypes—4/16 DdRr, 4/16 Ddrr, 4/16 ddRr, 4/16 ddrr

Phenotypes—4/16 round and red, 4/16 round and yellow, 4/16 wrinkled and red, 4/16 wrinkled and yellow

2.

DR Dr dR dr

DR GGRR GGR GgRR GgRr

Dr GGRr GGrr GgRr Ggrr

dR GgRR GgRr ggRR ggRr

dr GgRr Ggrr ggRr ggrr

Genotypes—1/16 GGRR, 2/16 GGRr, 1/16 GGrr, 2/16 GgRR, 4/16 GgRr, 2/16Ggrr, 1/16 ggRR, 2/16 ggRr, 1/16 ggrr

Phenotypes—9/16 yellow and smooth, 3/16 yellow and wrinkled, 3/16 green andsmooth, 1/16 green and wrinkled


Name ________________________________________LS–F: Student Worksheet


1. Perform a dihybrid cross between two Decorative corn plants—Ddrr × ddRr.Complete the Punnett Squares, list each different genotype, list each different phe-notype, and list the ratios of each genotype and phenotype. Use the following alleles:D = Round, d = wrinkled, R = Red, and r = yellow seed.

2. Perform a dihybrid cross between two decorative corn plants—DdRr × DdRr.Complete the Punnett Squares, list each different genotype, list each different phe-notype, and list the ratios of each genotype and phenotype. Use the following alleles:D= Round, d = wrinkled, R = Red, and r = yellow seed.


TS–A

Technical Supplement


1. How are genes distributed into gametes and recombined into zygotes?

Genes are distributed into gametes through a process called meiosis. In this process,which differs in detail, but not in the end result between male and female parts ofthe plant, the genes on each locus in an individual are distributed at random to thepollen cells or egg cells in a plant. Thus, if a plant has the genotype Bb at a locus, itcontains one B allele and one b allele at that locus. In the pollen from that plant, onehalf of the pollen grains will have the B allele and other half the b allele. Likewise, theegg cells will contain the alleles B and b for that particular trait. When two plantswhich are each Bb are crossed, the pollen and egg cells will combine randomly intozygotes. Unless outside forces change the probability, ¼ of the progeny will be BB,2/4 Bb, and ¼ bb. Thus, if a trait is dominant, both BB and Bb individuals will lookalike with ¾ of the offspring showing the dominant characteristic and ¼ showingthe recessive characteristic.

2. What are dominant and recessive genes?

A dominant gene, more precisely a dominant allele, is one which is expressed in anindividual regardless of the other allele at the same locus in an individual. In con-trast, a recessive allele is one which is not expressed in the presence of a dominantallele. In the example of the albino corn seedlings, the dominant allele allows normaldevelopment of green seedlings with normal growth in individuals which carry therecessive allele for albinism. Only when both recessive alleles for albinism are pres-ent at a locus does the plant lack chlorophyll and die.

3. What is the most probable genotype for the ears that were evaluated? What isthe most probable genotype of the parents of the ears that were evaluated?


principles of heredity: variation in corn -...

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