BIOLOGY 2C03 Chapter Notes - Chapter 19: Dihybrid Cross, Phenotypic Trait, Human Height
Document Summary
Single-gene traits: discontinuous (discrete) variation: discrete, sharply distinguishable categories, monohybrid cross: 3:1 ratio, dihybrid cross: 9:3:3:1 ratio. Polygenic and multifunctional traits: usually show continuous variation. Different genes contribute differently: major gene: oca2 on eye colour and skin tone, modifier (minor) genes: less influence. Each gene contributes an incremental amount to a phenotypic value: additive genes: alleles of each additive gene can be assigned a value of contribution. Multiple-gene hypothesis to explain kernel colour in wheat. Two genes: five phenotypic classes in a dihybrid cross. Number of phenotypes = 2n + 1: where n= the number of genes. More genes, more phenotypes, less demarcation between categories. The effect of multiple contributing genes on phenotypic. Corolla length in nicotiana longiflora (long flower tobacco) edward east in 1916. Conclusions: allelic segregation at multiple genes, environmental effects. Effect of the environment [general environmental variability (uncontrolled variation)] Effects of specific environmental factors on phenotypic variation.
