2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Objectives Identify the investigator whose studies formed the basis of modern genetics List characteristics that make the garden pea a good subject for genetic study Summarize the three major steps of Gregor Mendel’s garden pea experiments Relate the ratios that Mendel observed in his crosses to his data

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Many of your traits (physical characteristics), 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.

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mendel’s Studies of Traits Mendel’s Breeding Experiments Austrian monk named Gregor Johann Mendel. Mendel 1 st to develop rules that accurately predict patterns of heredity. form the basis of genetics, the branch of biology that focuses on hered ity.

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mendel’s Breeding Experiments Mendel experimented with garden pea heredity by cross-pollinating plants with different characteristics.

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Useful Features in Peas 1. Traits of the garden pea exist in 2 forms. 2. Controlled mating- male and female reproductive parts are within the same flower 3. Small, grows easily, matures quickly, and produces many offspring

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Monohybrid cross -involves one pair of contrasting traits Example: crossing a plant with purple flowers and a plant with white flowers

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mendel carried out his experiments in three steps: Step 1 Mendel allowed each variety of garden pea to self-pollinate for several generations to ensure that each variety was true-breeding for a particular trait; that is, all the offspring would display only one form of the trait. These true-breeding plants served as the parental generation in Mendel’s experiments. The parental generation, or P generation-the first two individuals that are crossed in a breeding experiment.

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Parental Generation

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Step 2 Mendel then cross- pollinated two P generation plants- offspring called the first filial generation, or F 1 generation. Step 3 Mendel allowed the F 1 generation to self-pollinate-called the second filial generation, or F 2 generation.

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mendel’s Results Each of Mendel’s F 1 plants showed only one form of the trait. But when the F 1 generation was allowed to self-pollinate, the missing trait reappeared in some of the plants in the F 2 generation. For each of the seven traits Mendel studied, he found a 3:1 ratio of plants expressing the contrasting traits in the F 2 generation.

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mendel’s 4 Hypothesis 1. For each inherited character, an individual has 2 copies of the gene, 1 from each parent 2. There are alternative versions of genes – alleles

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 3. When 2 different alleles occur together, 1 may be completely expressed & 1 may not affect appearance Dominate – trait expressed Recessive – trait not expressed when dominate allele present 4. Alleles for each gene separate during gamete formation

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Homozygous – the 2 alleles for a trait are the same Heterozygous – the 2 alleles for a trait are different

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Genotype – the alleles an individual has for a trait (genes) Phenotype – the physical appearance of a gene, it is determined by the genotype