Course: Animals Production

Unit Title: Genetics TEKS: 130.3(C)(6)(B)

Instructor: Ms. Hutchinson

Objectives:

After completing this unit of instruction, students will be able to:

A. Explain Gregor Mendel’s contribution to the scientific community;

B. Describe the interaction between chromosomes, genes, traits, and alleles;

C. Differentiate between genotype and phenotype;

D. List the 6 fundamental types of mating;

E. Workout punnett squares for one and two pair of contrasting traits; and

F. Calculate phenotypic and genotypic ratios.

Interest Approach:

Many of your traits, including the color and shape of your eyes, the texture of your hair,

and even your height and weight, resemble those of your parents. The passing of traits

from parents to offspring is called heredity. Humans have long been interested in

heredity. From the beginning of recorded history, we have attempted to alter crop plants

and domestic animals to give them traits that are more useful to us. Before DNA and

chromosomes were discovered, heredity was one of the greatest mysteries of science.

The scientific study of heredity began more than a century ago with the work of an

Austrian monk named Gregor Mendel. Mendel carried out experiments in which he bred

different varieties of garden peas. British farmers had performed similar breeding

experiments more than 200 years earlier. But Mendel was the first to develop rules that

accurately predict patterns of heredity. The patterns that Mendel discovered form the

basis of genetics, the branch of biology that focuses on heredity.

Mendel’s parents were peasants, so he learned much about agriculture. This knowledge

became invaluable later in his life. As a young man, Mendel studied theology and was

ordained as a priest. Three years after being ordained, he went to the University of

Vienna to study science and mathematics. There he learned how to study science through

experimentation and how to use mathematics to explain natural phenomena.

Mendel later repeated the experiments of a British farmer, T.A. Knight. Knight had

crossed a variety of the garden pea that had purple flowers with a variety that had white

flowers. All of the offspring of Knight’s crosses had purple flowers. However, when

two of the purple-flowered offspring were crossed, their offspring showed both white and

purple flowers. The white trait had reappeared in the second generation.

Mendel’s experiments differed from Knight’s because Mendel counted the number of

each kind of offspring and analyzed the data. Quantitative approaches to science, those

that include measuring and counting, were becoming popular in Europe. Mendel’s

method was on the cutting edge of research at the time.

Let’s now take a closer look at Mendel’s work and how it has evolved into what we call

Genetics today.

Curriculum & Instruction:

Curriculum

A. Explain Gregor Mendel’s contribution to the scientific community;

Gregor Mendel: • A) Geneticist who first developed the rules to predicting

the pattern of heredity

Instruction

PPT Slide 4-5 Who is the father of genetics?

– 1) Monk who did experiments with peas • B) Heredity

– 1. passing of traits such as coat color, polled or horned, height, etc. from parents to offspring

As discussed in the introduction Gregor Mendel was

the first to develop the rules for predicting heredity.

Heredity is the passing of traits such as coat color,

polled, or horned from generation to generation.

• C) Breeding Generations

– 1. P Generation • a) parental generation

– 2. F1 Generation • a) Filial Generation • b) 1st offspring of P Generation

– 3. F2 Generation • a) 2nd Filial Generation • b) offspring of F1 Generation

Mendel used three generations in his experiment.

He named the first the P generation for Parental

Generation or the beginning of the breeding program.

The first set of offspring from the P generation he

called the F1 Generation. The F stands for filial, which

in genetics relates to a generation or the sequence of

generations following the parental generation.

The offspring of this second generation he named the F2

generation or second filial generation.

Mendel’s initial experiments were monohybrid crosses.

A monohybrid cross is a cross that involves one pair of

contrasting traits. For example, crossing a plant with

purple flowers and a plant with white flowers is a

monohybrid cross. Mendel carried out his experiments

in three steps.

• D)3 Steps of Mendel’s Experiment

– 1. P Generation • a) Allowed each variety to self pollinate for

several generations – 1. ensure that all offspring would

What is heredity?

PPT Slide 6-7 What is the P generation? What is the F1 generation?

display only one form of a particular trait (flower color)

– 2. Crossbred the two strains of the P generation • - Recorded Data • - Resulted in all purple flowers

Step one. Mendel allowed each variety of garden peas

to self-pollinate for several generations. This method

ensured that each variety would display only one form

of a particular trait.

For example, a true-breeding purple flowering plant

should produce only plants with purple flowers in

subsequent generations.

These true-breeding plants served as the parental

generation in Mendel’s experiments. The parental

generation, or P generation, are the first two

individuals that are crossed in a breeding program.

Step two. Mendel than cross-pollinated two P

generation plants that had contrasting forms of a trait,

such as purple flowers and white flowers.

Mendel called the offspring the of the P generation the

first filial generation, or F1 generation. He then

examined each F1 plant and recorded the number of F1

plants expressed each trait.

– 3. Allowed the F1 Generation to self-pollinate

• a) Resulted in the F2 Generation • b) 1 out of every four flowers was white.

Step three. Finally, Mendel allowed the F1 generation

to self-pollinate. He called the offspring of the F1

generation plants the second filial generation or F2

generation. Again each of the F2 plants was

characterized and counted.

Each of Mendel’s F1 plants showed only one form of the

trait. The contrasting form of the trait had

disappeared. But when the F1 generation was allowed

to self-pollinate, the missing trait reappeared in some of

the plants in the F2 generation.

When Mendel crossed purple flowers with white

flowers, all of the offspring in the F1 generation had

purple flowers. In the F2 generation, 705 plants had

purple flowers and 224 plants had white flowers.

Go With the Flow Moment. You will need blank paper

and colored pencils or crayons. Have them recreate the

flow chart, in five to seven minutes, on overhead number

six.

B. Describe the interaction between chromosomes, genes,

traits, and alleles;

Traits: • A) Chromosomes and Genes are in pairs

– 1. One chromosome is contributed by each parent – 2. Chromosome Locus

• a) site where a gene is found on a chromosome

• B) Traits – 1. For each inherited trait an individual has, there

are two copies of that gene ( 1 from each parent)

– 2. Genes are what causes traits to appear • a) each version is called an allele • a) eye color, coat color, marbling, ribeye

area, etc.

Because chromosomes are in pairs, genes are also in

pairs. The location of a gene in a chromosome is called

a locus. For each locus in one of the members of a pair

of homologous chromosomes, a corresponding locus

occurs in the other member of that chromosome pair.

The transmission of genes from parents to offspring

depends entirely on the transmission of chromosomes

from parents to offspring. Genes are what cause traits

to be expressed.

PPT Slide 8 PPT Slide 9-10 What is a chromosome locus? What causes traits to appear?

For each inherited trait an individual has, there are two

genes for that specific trait, one from each parent.

Graphic Artist Moment to reconstruct the overhead into

their notebooks.

Homozygous vs. heterozygous III. Genes Located on Corresponding Homologous Chromosomes may:

• A) Correspond to each other – 1. homozygous

• B) Differ from each other – 2. heterozygous

• C) Genes on corresponding chromosomes that control the same trait are called alleles The genes located at corresponding loci in homologous

chromosomes may correspond to each other or contrast

with each other in the way that they control a trait.

If they correspond, the individual is said to be

homozygous at the locus; if they differ, the individual is

said to be heterozygous. Those genes that occupy

corresponding loci in homologous chromosomes but

that affect the same character in different ways, black

or red coat color, are called alleles. Genes that are alike

and that affect the character in the same way are called

identical alleles.

Alleles:

• A) Homozygous (BB or bb)

PPT Slide 11 What is homozygous? What is heterozygous? What is an allele?

PPT Slide 12

– 1. both alleles are the same • B) Heterozygous (Bb)

– 1. two alleles are different • C) The dominant (capital) allele is always expressed when

it is present • D) The recessive allele is only expressed when both copies

of the gene are recessive

The geneticist usually illustrates the genes by

alphabetical letters. When the genes at corresponding

loci on homologous chromosomes differ, one of the

genes often overpowers, or dominates, the expression of

the other. This allele is called dominant.

The allele whose expression is suppressed is said to be

recessive. The dominant allele is symbolized by a

capital letter; the recessive allele is symbolized by a

lower case letter.

For example, in cattle, black hair color is dominant to

red hair color, so we let B = black and b = red. Three

combinations of the genes are possible. BB, Bb, or bb.

Both BB animals and bb animals are homozygous for

the genes that determine hair color, but one is

homozygous dominant (BB) and the other is

homozygous recessive (bb).

The animal that is Bb is heterozygous; it has allelic

genes. The only red animal will result from the bb

combination. Keep in mind that dominant genes are

not necessarily “good” nor or recessive genes always

“bad.”

C. Differentiate between genotype and phenotype. Genotype vs. Phenotype:

• A) Genotype – 1. amount, order, and type of genes an individual

has – 2. genetic make-up of an individual

• B) Phenotype – 1. Physical traits an individual possesses – 2. Doesn’t take into account masked traits only

expressed or dominant traits

What is an example of homozygous alleles? What is an example of heterozygous alleles?

PPT Slide 13 What is the genotype? What is the phenotype?

The actual configuration of genes in an animal is called

the genotype. For any given trait there are three

possible genotypes AA, Aa, or aa. Genotype is looking

at the specific make up of that organism. In contrast

phenotype depicts the physical appearance of the

animal. Phenotype is looking at the broader picture.

Phenotype doesn’t tell us what traits are masked, the

recessive traits; it only depicts the dominant traits that

mask the recessive ones. Review

Gregor Mendel is known as the father of genetics. He was

the founder of a new way at looking at how traits are

passed down that he called heredity. He discovered the

existence of dominant and recessive traits. That we get one

gene from each parent to make a pair of genes that controls

a specific trait. He conducted a simple, yet effective,

experiment using peas with white and purple flowers.

From this knowledge science made progress to where it is

today. We know that genes are found on chromosomes,

and that an individual has pairs of chromosomes, one

contributed from each parent. The genes on chromosomes

are what control all the traits that make up an organism,

from height to eye color. A specific trait is controlled by

genes found on a very specific spot of homologous

chromosomes known as the locus. If both genes are the

same on both chromosomes the individual is said to be

homozygous; if one of the genes is different it is said to be

heterozygous.

Genotype is the way geneticists describe the makeup of an

organism. Is it heterozygous or homozygous? Examples

of a homozygous gene would be BB or bb, and

heterozygous would be Bb. Phenotype is the physical

appearance of an animal. Does it have a black coat or a red

one? Phenotype doesn’t take into consideration the

recessive genes that are masked by the dominant ones.

Dominant & Recessive Genes Investigate! (interest for dominant and recessive genes)

Have students look at their hands for scars, wrinkles, hair,

and veins. (about 30 seconds)

Raise your hand if you have hair above your knuckles.

PPT Slide 14

Good, thank you. The presence of hair above the knuckles

is caused by a dominant allele, H. Those of you who have

no hair above your knuckles, what is your genotype for this

trait? (hh is the only possibility) Under what

circumstances could a parent without hair above their

knuckles produce a child with hair above their knuckles?

(The second parent must have hair above their knuckles)

D. List the 6 fundamental types of mating;

Monohybrid Crosses

• A. Three class genotypes

– 1. Homozygous Dominant = BB

– 2. Homozygous Recessive = bb

– 3. Heterozygous = Bb

• B. B = Black & b = Red

• C. Six possible crosses:

BB x BB, BB x Bb, BB x bb, Bb x Bb, Bb x bb, bb x bb

Using just this information can you think of a breeding

program where the recessive gene was used to develop

an entirely new breed of beef cattle? (Red Angus is an

example of how a breeding program successfully

isolated a recessive gene and through careful

management used that gene to found a new breed.)

Little Professor

When I say little professor I would like each of you to find

a partner. Keep in mind that you need to be in pairs with

an area large enough for both of your notebooks. Little

Professor.

Good job guys. I now need one person in each group to

raise your hand. Those of you with your hands up will be

Little Professor I and your partners will be Little Professor

II. Little Professor II’s. For the next couple of minutes

you are not to listen to me. You may read, daydream, or

put your head down. The only thing you can’t do is leave

your seats, talk, or be a disruption.

E. Workout punnett squares for one and two pair of

contrasting

traits; and

F. Calculate phenotypic and genotypic ratios.

Predicting Ratios:

PPT Slide 15 What are the 3 classes of genotypes? What are the 6 possible crosses?

B B

B B

B

B

B

B B

B

B

B

• Homozygous x Homozygous

• A. Genotype

– 2. Results in a homozygous dominant zygote

• B. BB x BB

– Phenotype:

– 1. Each parent can only contribute a dominant gene

Little Professor I’s, you have the next thirty seconds to

instruct your partners on this information, be sure they get

the most important information into their notebooks.

Little Professor I’s, it is now your turn to take a break

while I talk with the Little Professor II’s.

B B

B B

B

B

B

b B

b

B

b

• Homozygous x Heterozygous

• E. BB x Bb

– 1. Genotypic Ratio

• 2 BB : 2 Bb

– 2. Phenotypic Ratio

PPT Slide 16 PPT Slide 17

• a) 4 Black color

Little Professor II’s, take the next thirty seconds, as the

experts in your field, to instruct your partners.

Little Professor I’s, it’s your turn to listen to me, Little

Professor II’s you know the routine

B B

b Bb Bb

b Bb Bb

• Homozygous x Homozygous

• F. BB x bb

– Genotypic ratio:

• 0BB : 4Bb

• All offspring will be heterozygous

– Phenotypic ratio: 4 black coat : 0 red coat

Little Professor I’s take the next thirty seconds to teach

your partners.

Little Professor II’s you are back with me and Little

Professor I’s it is your turn to relax.

B b

B B

B

B

b

PPT Slide 18 PPT Slide 19

b

B

b

b

b

• G. Bb x Bb

– 1. Phenotypic Ratio

• a) 3 black to 1 red or 3:1

– 2. Genotypic Ratio

• a) 1BB: 2Bb: 1bb

Little Professor II’s, take the next minute to teach your

partners this new information.

Very good job! Little Professor II’s take some well-

deserved time off, Professor I's your back with me.

b b

B B

b

B

b

b bb bb

• H. Bb x bb

– 1. Genotypic Ratio

• a) 2Bb: 2bb

– 2. Phenotypic Ratio

• a) 2 black to 2 red

Little professors’, take the next thirty seconds to teach your

partners this new information.

One last time Little Professor II’s please come back to me.

Little prof’s I take the next couple of minutes to relax.

PPT Slide 20

b b

b bb bb

b bb bb

• B. Homozygous x Homozygous

• . bb x bb

- All will be red

• Genotypic Ratio

- 4bb : 0

• Phenotypic Ratio

- 4 red coats : 0 black coats

Take the next thirty seconds to instruct your partners on this

information.

Once they have finished, distribute the worksheet to each

student and allow them three minutes to complete the

punnett squares. Each student is to work out the punnett

square and write the genotypic and phenotypic ratios next

to each square.

In your little professor pairs I would like each of you to

look at the information presented in the current overhead.

Just like in the past six examples, B is dominant and black,

b is recessive and red.

In addition I have added a second trait. P is dominant for

polled and p is recessive for horned.

You are starting a new SAE, the bull you have bought has a

genotype of BbPp and you plan to breed him to the heifer

you just bought. Her genotype is also heterozygous for

both traits.

Take the next five minutes, working with your partner to

complete worksheet three. I also ask you to figure out the

genotypic and phenotypic ratio for this cross. Good luck,

PPT Slide 21

begin.

Multiple Gene Pairs:

• A. Mating

– 1. B = Black & b = Red

– 2. P = Polled & p = horned

• B. Bull

– 1. BbPp

• C. Cow

– 1. BbPp

• D. What will the phenotypic & genotypic ratios be?

P

B

P

b

p

B

p

b

P

B

P

P

B

B

P

P

B

b

P

p

B

B

P

p

B

b

P

b

P

P

B

b

P

P

b

b

P

p

B

b

P

p

b

b

p

B

P

p

B

B

P

p

B

b

p

p

B

B

p

p

B

b

p

b

P

p

B

b

P

p

b

b

p

p

B

b

p

p

b

b

• E. Genotypic Ratio

– 1. 1 PPBB: 2 PPBb: 1 PPbb: 2 PpBB: 4 PpBb: 2

Ppbb: 2 ppBb: 1ppbb

• F. Phenotype

– 1. 9 polled and black

– 2. 3 polled and red

– 3. 3 horned and black

– 4. 1 horned and red

Practice it!

As a fun and different way to let the students practice working out

PPT Slide 22-24

punnett squares, pair students up (according to their ability) and

have each student get a piece of sidewalk chalk. Outside on the

concrete have the students work out a few problems using the

punnett square. Each student needs to use their own color chalk so

that the students can get a separate grade for the practice.

Review & Instruction:

Objectives will be reviewed before examinations. Exams will be developed based on objectives as

taught in class.

Instructional Support:

A. References

a. Colorado Agriscience Curriculum

B. Teaching Aids & Equipment:

a. Genetics PPT

b. Genetics Student PPT

c. Colored Pencils

d. Mendel & Genetics Quiz

e. Punnett Square Worksheet

f. Sidewalk Chalk

g. Genetics Test Review

h. Genetics Test

C. Facilities:

a. Agriculture classroom