The principles of genetic analysis that we have described for a single locus can be extended to the study of alleles at two loci simultaneously. Analysis of two loci in parallel is required for genetic mapping and can also reveal gene interactions. These techniques are very useful for both basic and applied research. Before discussing these techniques, we will first revisit Mendel’s classical experiments.
- 6.1: Dihybrid Crosses
- Mendel's Second Law, also called the Law of Independent Assortment, argues that two loci assort independently of each other during gamete formation. The commonly observed 9:3:3:1 phenotypic ratio that is predicted from this law can also be obtained using Punnett Square
- 6.2: Epistasis and Other Gene Interactions
- Epistasis (which means “standing upon”) occurs when the phenotype of one locus masks, or prevents, the phenotype of another locus. Thus, following a dihybrid cross fewer than the typical four phenotypic classes will be observed with epistasis. As we have already discussed, in the absence of epistasis, there are four phenotypic classes among the progeny of a dihybrid cross.
- 6.3: Example of Multiple Genes Affecting One Character
- Most aspects of the fur phenotypes of common cats can be explained by the action of just a few genes. Other genes, not described here, may further modify these traits and account for the phenotypes seen in tabby cats and in more exotic breeds, such as Siamese.
- 6.E: Genetic Analysis of Multiple Genes (Exercises)
- These are homework exercises to accompany Nickle and Barrette-Ng's "Online Open Genetics" TextMap. Genetics is the scientific study of heredity and the variation of inherited characteristics. It includes the study of genes, themselves, how they function, interact, and produce the visible and measurable characteristics we see in individuals and populations of species as they change from one generation to the next, over time, and in different environments.
- 6.S: Genetic Analysis of Multiple Genes (Summary)
- These are the summary for Chapter 6 of Nickle and Barrette-Ng's "Online Open Genetics" TextMap.
Thumbnail: Coat color in animals is an example of a trait that is controlled by more than one locus. (Flickr-Gossamer1013-CC:AND).