chapter 13 mendel and the gene

1. Chapter 13 MENDEL AND THE GENE Why do we look like family members or not?

3. History Mendel, an Austrian monk, repeated Knight�s experiments: Also used true-breeding peas and studied 7 different traits, fig 13.2. Cross-fertilized peas showing two variations of the same trait, ex. round peas vs. wrinkled peas.

6. Mendel Studied a Single Trait Mendel cross-fertilized two plants, one with white flowers with one with purple flowers. The hybrids, the F1 generation, all had purple flowers. Studying one trait through cross-fertilization is termed a monohybrid cross.

8. Mendel Studied a Single Trait Mendel�s experiments cont�d Mendel allowed F1 generation plants to self- fertilize. Their offspring, the F2 generation, expressed (demonstrated) both purple and white flowers. The ratio of plants with purple to white flowers was always 3:1. Where did these white flowered plants come from?

10. Mendel Studied a Single Trait Mendel cont�d The F1 generation plants all resembled only parent plant; i.e. one variation of the trait is dominant. The F2 generation showed plants with both variations of the character, purple and white. The variation of the trait that was only seen in the F2 generation (white flowers) is recessive.

11. Mendel Studied a Single Trait Mendle cont�d The F2 generations were allowed to self-fertilize. Looking at the F3 generation, Mendel discovered that the F2 generation actually consisted of 3 different types of plants: Pure breeding purple Not pure breeding purple (produced both purple and white flowered plants. Pure breeding white. The ratio was actually 1:2:1.

12. Mendel Studied a Single Trait Conclusions (cross involving 1 trait)

13. Genes and Mendel�s Findings Traits are carried by genes. An individual has 2 genes or alleles for each trait, 1 on each homologous chromosome. Meiosis results in separation of the homologous chromosomes and the alleles so that each is carried by a different gamete.

14. Genes and Mendel�s Findings An individual with 2 identical alleles is said to be homozygous, while an individual with 2 different alleles is said to be heterozygous. The genetic make-up of an individual is its genotype. The appearance or expression of the genotype is called its phenotype.

15. Genes and Mendel�s Findings Mendel�s results can be predicted using Punnett squares. Dominant genes are represented by uppercase letters, ex. round peas (R) . Expressed when there is 1 or 2 dominant alleles present. Recessive genes are represented by lowercase letters, ex. wrinkled peas (r). Only expressed when there are 2 recessive alleles present.

17. Genes and Mendel�s Findings Mendels� Principle of Segregation, fig 13.7:

19. Mendel Studied 2 Traits Mendel then looked at two traits simultaneously � dihybrid cross. Ex. plants that produced round (R), yellow (Y) peas and plants that produced wrinkled (r), green (y) peas. The pure breeding parents� genotypes were RRYY and rryy, fig 13.5. What is the genotype and phenotype of the F1 generation? The F2 generation?

21. Genes and Mendel�s Findings Mendel�s Principle of Independent Assortment:, fig 13.8.

28. Peas Are Easy Co dominance: Some phenotypes represent both alleles, ex. blood types. ABO Blood groups - CoDominance 2 dominant alleles, A and B, one recessive allele, i. Alleles code for different RBC membrane proteins. These protein act as antigens (can cause an immune response). Immune response = antibodies.

29. Peas Are Easy ABO Blood Groups, cont�d Type A blood type has IA,IA or IA,i alleles Type B blood type has IB, IB or IB,i alleles Type AB blood type has IA, IB alleles Type O blood type has i, i alleles (recessive form, no antigens on their RBCs). Rh blood group: the Rh factor consists of 8 different antigens. A person that has even one of these antigens is Rh+ while those having none of the antigens is Rh-.

34. Pedigree of a family with Huntington�s Disease