Chapter 12: Mendel and Heredity

1. Chapter 12: Mendel and Heredity Page 267

2. Section 12.1: Origins of Hereditary Science • An Austrian monk, Gregor Mendel studied the subject of heredity using pea plants • Heredity is the passing on of characteristics from parents to offspring • Genetics is the field of biology that deals with heredity • These inherited characteristics are called traits

3. Mendel’s Pea Plants • Mendel chose pea plants as his main focus of study because they reproduce sexually • Most times, pea plants self-pollinate with their own male and female gametes • However, Mendel controlled the pollination between plants by dusting the pollen grains of one flower on the pistil of another flower • He would then bag the flowers so that no other flower could pollinate his test pea plants and he would also know which flowers where the “parent” generation • This is called cross pollination

5. Mendel observed traits one at a time and only picked plants that were true-breeding for a specific trait • Ex. When using purple flowered pea plants, these pea plants would come from a line of purple flowered pea plants that only bred purple flowered plants for many generations • He observed a total of seven pairs of traits

6. Page 268, Figure 2

7. Mendel took these true-breeding pea plants and crossed them to produce new plants or hybrids A hybrid is the offspring of parents that have different forms of a trait such as tall and short height Monohybrid crosses are called so because they are crosses of two parents with a single trait difference

8. Ex. P1 (Parental Generation) True-breeding Purple plant x True-breeding White plant Result: All children are Purple F1 generation  F1 (First Filial Generation) Purple offspring of P1 generation self pollinate Result: 3 Purple plants : 1 White plant F2 generation

10. Section 12.2: Mendel’s Theory • Mendel concluded that each organism has two versions of a gene that control each of its traits • The different gene versions are alleles • Each plant had two alleles of a gene that determined one trait • Ex. Tall plants could have been TT, Tt and short plants could only be tt • Each parent contributes one allele to their offspring

11. The Rule of Dominance The observed (expressed) trait was dominant, the trait that disappears is recessive When all the F1 were tall, the dominant trait here was tall and the short trait was recessive  Ex. P1 (Parental Generation) True-breeding Tall plant (TT) x True-breeding Short plant (tt) Result: All children are over six feet tall F1 generation (Tt)  F1 (First Filial Generation) Tall offspring of P1 generation self pollinate Tt x Tt Result: 3 Tall plants : 1 short plant F2 generation

12. The Law of Segregation Two alleles for each trait must separate when gametes are formed A parent passes on at random only one allele for each trait to each offspring The law of segregation says when an organism produces gametes, each pair of alleles is separated and each gamete has an equal chance of receiving either one of the alleles

13. Phenotype vs. Genotype The way an organism looks or behaves is called a phenotype The genetic combination of an organism is the genotype derp Ex. Tallness is a plant’s phenotype but the genotype can be Tt or TT Genotype determines phenotype

14. Homozygous vs. Heterozygous An organism is homozygous for a trait if both alleles are the same Ex. TT or tt An organism is heterozygous for a trait if the two alleles are different Ex. Tt

15. Dihybrid Cross • A dihybrid cross is one between two organisms for two different traits • Ex. Color and height of the plant • Law of independent assortment says that during gamete formation, the alleles of each gene segregate independently • The inheritance of one trait does not affect the inheritance of another

16. Dihybrid Cross

17. Punnett Squares A man named Reginald Punnett found a way to predict the genotypes of offspring when the parent’s genotypes are known In pea plants, yellow peas are dominant over green peas. Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross between a plant heterozygous/hybrid for yellow (Yy) peas and a plant homozygous/purebred for green (yy) peas.

18. Draw a Square divided into 4 boxes

19. Possible gametes from each parent is found on the outside y Y Yellow y y Green

20. Fill in the children’s gametes looking along the side and top y Y Yellow Yy y yy Yy yy y Green

21. Determine how many of each phenotypes result and how many genotypes result y Y Yellow Phenotypic ratio: 2 Yellow: 2 Green Genotypic ratio: 2 Yy: 2yy y Yy yy Yy yy y Green