Types of biological variation Discontinuous (qualitative) variation : simple alternative

1. Types of biological variation • Discontinuous (qualitative) variation: simple alternative • forms; alternative phenotypes; usually due to alternative • genotypes • often due to interactions of dominant and recessive • alleles of genes • common alternatives due to polymorphism • rare alternatives due to mutation (vs. wild type) • Continuously variable (quantitative) traits: no distinct increments; most common variation; due to polygenes • and/or significant non-genetic influence.

2. Development that is genetically driven Fig. 1-17

3. Development that is environmentally driven Fig. 1-18

4. Development that is driven by interactions between genes and the environment Fig. 1-19

5. Norm of reaction: phenotypic outcome of the interactions of genotype and environment; characteristic for each genotype Developmental noise: random influences on phenotype that result in random individual variations

6. Drosophila melanogaster (wild-type) Fig. 1-20

7. Fig. 1-20

8. Development resulting from interactions between genes, environment and “noise” Fig. 1-23

9. Chapter 2 Overview Fig. 2-1

10. Simple monohybrid inheritance • single gene (allele pair) • simple dominance of one allele

11. Mendel’s explanation of simple monohybrid inheritance • Genes are particulate • 2. Genes in pairs and can be • different forms (alleles) • 3. Halving of pairs in gametogenesis • 4. Alleles separate (segregate) in • gametogenesis • 5. Fertilization is random Fig. 2-7

12. Testcross to test/demonstrate heterozygosity Testcross: cross possible heterozygote to homozygous recessive Fig. 2-8

13. Dihybrid inheritance Fig. 2-10

14. Dihybrid inheritance Fig. 2-11

15. Estimating the likelihoods of events • Independent events: • Compute the likelihood of each event • Compute the product of those likelihoods • Dependent (mutually exclusive) events: • Compute the likelihood of each event • Compute the sum of those likelihoods

16. Problem: predict the phenotypic ratios expected among the progeny of the cross A/a ; b/b X A/a ; B/b Solution: use a branch diagram

17. Dihybrid inheritance Fig. 2-11

18. Problem: predict the phenotypic ratios expected among the progeny of the cross A/a ; b/b X A/a ; B/b Solution: use a branch diagram p. 155

19. Conventional symbols used in pedigree analysis Fig. 2-12

20. Analysis of a rare autosomal, recessive phenotype Typical: affected males and females; affected individuals have unaffected parents Fig. 2-13

21. Analysis of a autosomal dominant phenotype Typical: affected males and females; about half of progeny of affected individual are affected Fig. 2-16

22. T.H. Morgan’s analysis of the sex linkage of white Fig. 2-24

23. Repeat from previous slide Fig. 2-24

24. Analysis of a rare sex-linked, recessive phenotype Typical: almost exclusively affected males; mothers of affected sons are carriers; appears to “skip” generations Fig. 2-25

25. Mirabilis jalapa Fig. 2-30

26. Schematic of organellar/cytoplasmic inheritance Fig. 2-31

32. X2 (Chi-square) test: assesses the likelihood that a deviation from expectations can be accepted Example: Do results of a dihybrid cross reflect linkage? Products of a dihybrid (A/a B/b) testcross AB 142 ab 133 Ab 113 aB 112 Parental types Recombinant types

33. X2 (Chi-square) test: assesses the likelihood that a deviation from expectations can be accepted Example: Do results of a dihybrid cross reflect linkage? 1st step: Make “null hypothesis” – genes are not linked Predicts 1:1:1:1 ratio of gamete genotypes 2nd step: Compute X2 =  (O-E)2 / E 3rd step: Determine degrees of freedom (number of independent measurements) 4th step: Consult X2 chart of critical values