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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 - PowerPoint PPT Presentation
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Types of biological variation
Discontinuous (qualitative) variation: simple alternativeforms; 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 drivenFig. 1-17
Development that is environmentally drivenFig. 1-18
Development that is driven by interactions between genes and the environmentFig. 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
Fig. 1-20
Development resulting from interactions between genes, environment and noiseFig. 1-23
Chapter 2 OverviewFig. 2-1
Simple monohybrid inheritance
single gene (allele pair)simple dominance of one allele
Fig. 2-7Genes 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
Mendels explanation of simple monohybrid inheritance
Fig. 2-8Testcross to test/demonstrate heterozygosityTestcross: cross possible heterozygote to homozygous recessive
Fig. 2-10Dihybrid inheritance
Fig. 2-11Dihybrid 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 theprogeny of the cross A/a ; b/b X A/a ; B/b
Solution: use a branch diagram
Fig. 2-11Dihybrid inheritance
p. 155Problem: predict the phenotypic ratios expected among theprogeny of the cross A/a ; b/b X A/a ; B/b
Solution: use a branch diagram
Conventional symbols used in pedigree analysisFig. 2-12
Fig. 2-13Analysis of a rare autosomal, recessive phenotypeTypical: affected males and females; affected individuals have unaffected parents
Analysis of a autosomal dominant phenotypeFig. 2-16Typical: affected males and females; about half of progeny of affected individual are affected
T.H. Morgans analysis of the sex linkage of whiteFig. 2-24
Fig. 2-24Repeat from previous slide
Fig. 2-25Analysis of a rare sex-linked, recessive phenotypeTypical: almost exclusively affected males; mothers of affected sons are carriers; appears to skip generations
Fig. 2-30Mirabilis jalapa
Fig. 2-31Schematic of organellar/cytoplasmic inheritance
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 142ab 133Ab 113aB 112 Parental types
Recombinant types
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