
OutliningAs you read, make an outline about Mendel’s work. Use the red headings for the main ideas and the blue headings for the supporting ideas.

Mendel’s WorkI. Mendel’s Experiments

A. Crossing Pea PlantsB. The F1 OffspringC. The F2 OffspringD. Experiments With Other

TraitsII. Dominant and Recessive

AllelesA. Genes and AllelesB. Alleles in Mendel’s

CrossesC. Symbols for AllelesD. Significance of Mendel’s

Contribution

- Mendel’s Work


Data Sharing Lab

Click the PHSchool.com button for an activity about sharing data for the Skills Lab Take a Class Survey.

- Mendel’s Work

http://phschool.com/webcodes10/index.cfm?fuseaction=home.gotoWebCode&wcprefix=ced&wcsuffix=3031


End of Section:Mendel’s Work


Percentages One way you can express a probability is as a percentage. A percentage (%) is a number compared to 100. For example, 50% means 50 out of 100.Suppose that 3 out of 5 tossed coins landed with heads up. Here’s how you can calculate what percent of the coins landed with heads up.1. Write the comparison as a fraction.

3 out of 5 = 3/52. Multiply the fraction by 100% to express it as a percentage.

3/5 x 100%/1 = 60%

- Probability and Heredity


Percentages

Practice Problem

Suppose 3 out of 12 coins landed with tails up. How can you express this as a percent?

25%


Genetics: The Science of Heredity - Probability and Heredity

A Punnett SquareThe diagrams show how to make a Punnett square. In this cross, both parents are heterozygous for the trait of seed shape. R represents the dominant round allele, and r represents the recessive wrinkled allele.


Probability and GeneticsIn a genetic cross, the allele that each parent will pass on to its offspring is based on probability.


What Are the Genotypes?

Mendel allowed several F1 pea plants with yellow seeds to self-pollinate. The graph shows the approximate numbers of the F2 offspring with yellow seeds and with green seeds.




Yellow–6,000; green–2,000

Reading Graphs:

How many F2 offspring had yellow seeds? How many had green seeds?




8,000; 75% have yellow peas and 25% have green peas.

Calculating:

Use the information in the graph to calculate the total number of offspring that resulted from this cross. Then calculate the percentage of the offspring with yellow peas, and the percentage with green peas.




Both parents probably had the genotype Bb.

Inferring:

Use the answers to Question 2 to infer the probable genotypes of the parent plants. (Hint: Construct Punnett squares with the possible genotypes of the parents.)



Phenotypes and GenotypesAn organism’s phenotype is its physical appearance, or visible traits, and an organism’s genotype is its genetic makeup, or allele combinations.


CodominanceIn codominance, the alleles are neither dominant nor recessive. As a result, both alleles are expressed in the offspring.


Building VocabularyAfter you read the section, reread the paragraphs that contain definitions of Key Terms. Use all the information you have learned to write a definition of each Key Term in your own words.


Key Terms: Examples:probability Probability is a number that describes how likely it is

that an event will occur.

Punnett square A Punnett square is a chart that shows all the possible combinations of alleles that can result from a genetic cross.

phenotype An organism’s phenotype is its physical appearance, or visible traits.

genotype An organism’s genotype is its genetic makeup, or allele combinations.

Key Terms: Examples:homozygous

heterozygous

codominance

An organisms that has two identical alleles for a trait is said to be homozygous.

An organisms that has two different alleles for a trait is heterozygous for that trait.

In codominance, the alleles are neither dominant nor recessive.


Links on Probability and Genetics

Click the SciLinks button for links on probability and genetics.


http://www.scilinks.org/fromoutside.asp?sciLINKSNumber=scn-0332&type=student


End of Section:Probability and

Heredity


Meiosis Terminology•Gamete – a mature male (sperm) or female (egg) that unites with another cell to form a new organism.

•Haploid – a cell or organism having only one complete set of chromosomes.

•Diploid – a cell or organism having two similar complements of chromosomes.

Genetics: The Science of Heredity - The Cell and Inheritance

MeiosisDuring meiosis, the chromosome pairs separate and are distributed to two different cells. The resulting sex cells have only half as many chromosomes as the other cells in the organism.


Punnett SquareA Punnett square is actually a way to show the events that occur at meiosis.


A Lineup of GenesChromosomes are made up of many genes joined together like beads on a string. The chromosomes in a pair may have different alleles for some genes and the same allele for others.

You have 23 pairs of chromosomes and about 35,000 genes in each of your body cells.

Each of these genes control a trait!


Meiosis KM 25


Meiosis KM 26


Meiosis KM 27

In humans …

• 23 chromosomes donated by each parent (total = 46 or 23 pairs).

• Gametes (sperm/ova):Contain 22 autosomes and 1 sex chromosome.Are haploid (haploid number “n” = 23 in humans).

• Fertilization/syngamy results in zygote with 2 haploid sets of chromosomes - now diploid.

Diploid cell; 2n = 46. (n=23 in humans)

• Most cells in the body produced by mitosis.

• Only gametes are produced by meiosis.


Meiosis KM 28

Chromosome numbers

All are even numbers – diploid (2n) sets of homologous chromosomes!

Ploidy = number of copies of each chromosome. Diploidy


Meiosis KM 29

Meiosis – key differences from mitosis• Meiosis reduces the number of chromosomes by half.• Daughter cells differ from parent, and each other.• Meiosis involves two divisions, Mitosis only one.• Meiosis I involves:

Synapsis – homologous chromosomes pair up. Chiasmata form (crossing over of non-sister chromatids).In Metaphase I, homologous pairs line up at metaphase plate.In Anaphase I, sister chromatids do NOT separate.Overall, separation of homologous pairs of chromosomes, rather than sister chromatids of individual chromosome.


30


Animation


Identifying Supporting EvidenceAs you read, identify the evidence that supports the hypothesis that genes are found on chromosomes. Write the evidence in a graphic organizer.

Chromosomes are important in inheritance.

Grasshoppers:24 chromosomes in body

cells, 12 in sex cells.

Fertilized egg has24 chromosomes.

Alleles exist in pairs in

organisms.

- The Cell and Inheritance


Meiosis Summary• Meiosis is the process by which the number of

chromosomes is reduced by half to form sex cells.

• Meiosis I: The duplicated chromosomes divide into two cells, each with half the number of chromosomes.

• In Meiosis I, the members of each chromosome pair separate and end up in different cells.

• Meiosis II: The two cells divide once more, producing sex cells that have half as many chromosomes as the body cells.


Links on Meiosis

Click the SciLinks button for links on meiosis.


http://www.scilinks.org/fromoutside.asp?sciLINKSNumber=scn-0333&type=student


Chromosomes

Click the Video button to watch a movie about chromosomes.



End of Section:The Cell and Inheritance

Genetics: The Science of Heredity - The DNA Connection

The DNA CodeChromosomes are made of DNA. Each chromosome contains thousands of genes. The sequence of bases in a gene forms a code that tells the cell what protein to produce.


How Cells Make ProteinsDuring protein synthesis, the cell uses information from a gene on a chromosome to produce a specific protein.


Protein Synthesis Activity

Click the Active Art button to open a browser window and access Active Art about protein synthesis.

- The DNA Connection


MutationsMutations can cause a cell to produce an incorrect protein during protein synthesis. As a result, the organism’s trait, or phenotype, may be different from what it normally would have been.


SequencingSequence is the order in which the steps in a process occur. As you read, make a flowchart that shows protein synthesis. Put each step in the flowchart in the order in which it occurs.

Protein SynthesisDNA provides code to form messenger RNA.

Messenger RNA attaches to ribosome.

Transfer RNA “reads” the messenger RNA.

Amino acids are added to the growing protein.



Protein Synthesis

Click the Video button to watch a movieabout protein synthesis.



End of Section:The DNA

Connection


Graphic Organizer

Transfer RNA

RNA

Messenger RNA

includes

Carry amino acids

functions to functions to

Copy the coded message from the

DNA

Carry the message to the ribosome in

the cytoplasm

Add amino acids to the growing

protein


End of Section:Graphic Organizer

table of contents

Documents

science of heredity9

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