1. Genetics: From Genes to Genomes
Powerpoint to accompany
Genetics: From Genes to Genomes
Second Edition
Hartwell ● Hood ● Goldberg ● Reynolds ● Silver ● Veres
Chapter 3
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2. Complexities in relating genotype to phenotype
Extensions to Mendel
Complexities in relating
genotype to phenotype

3. Outline of extensions to Mendel’s analysis
Single-gene inheritance
In which pairs of alleles show deviations from complete dominance and recessiveness
In which different forms of the gene are not limited to two alleles
Where one gene may determine more than one trait
Multifactorial inheritance in which the phenotype arises from the interaction of one or more genes with the environment, chance, and each other

4. Dominance is not always complete
Crosses between true-breeding strains can produce hybrids with phenotypes different from both parents
Incomplete dominance
F1 hybrids that differ from both parents express an intermediate phenotype. Neither allele is dominant or recessive to the other
Phenotypic ratios are same as genotypic ratios
Codominance
F1hybrids express phenotype of both parents equally

5. Summary of dominance relationships
Figure 3.2
Fig. 3.2

6. Incomplete dominance in snapdragons
Fig. 3.3
Figure 3.3

7. Codominant lentil coat patterns
Figure 3.4a
Fig. 3.4a

8. Codominant blood group alleles
Figure 3.4b
Fig. 3.4b

9. Do variations on dominance relations negate Mendel’s law of segregation?
Dominance relations affect phenotype and have no bearing on the segregation of alleles
Alleles still segregate randomly
Gene products control expression of phenotypes differently
Mendel’s law of segregation still applies
Interpretation of phenotype/genotype relation is more complex

10. A gene can have more than two alleles
Genes may have multiple alleles that segregate in populations
Alleles may be unique to every pair of alleles in an individual