Chapter 8 Summary

The topics covered in this chapter can be summarized as follows:

  • Phenotypes depends on the alleles that are present, their dominance relationships, and sometimes also interactions with the environment and other factors.
  • The alleles of different loci are inherited independently of each other, unless they are genetically linked.
  • Many important traits show continuous, rather than discrete variation. These are called quantitative traits.
  • Many quantitative traits are influenced by a combination of environment and genetics.
  • The expected phenotypic ratio of a dihybrid cross is 9:3:3:1, except in cases of linkage or gene interactions that modify this ratio.
  • Modified ratios from 9:3:3:1 are seen in the case of recessive and dominant epistasis, duplicate genes, and complementary gene action. This usually indicates that the two genes interact within the same biological pathway.
  • There are other factors that alter the expected Mendelian ratios.


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Introduction to Genetics Copyright © 2023 by Natasha Ramroop Singh, Thompson Rivers University is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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