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.

Development that is genetically driven Fig. 1-17

Development that is environmentally driven Fig. 1-18

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

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

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

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

Chapter 2 Overview Fig. 2-1

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

Fig 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 Mendel’s explanation of simple monohybrid inheritance

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

Fig Dihybrid inheritance

Fig Dihybrid inheritance

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

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

Fig Dihybrid inheritance

p. 155 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

Conventional symbols used in pedigree analysis Fig. 2-12

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

Analysis of a autosomal dominant phenotype Fig Typical: affected males and females; about half of progeny of affected individual are affected

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

Repeat from previous slide

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

Fig Mirabilis jalapa

Fig Schematic of organellar/cytoplasmic inheritance

X 2 (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

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