Essential Idea:
Genes may be linked or unlinked
and are inherited accordingly
Understandings:
- Gene loci are said to be linked if on the same chromosome
- Unlinked genes segregate independently as a result of meiosis
- Variation can be discrete or continuous
- The phenotypes of polygenic characteristics tend to show continuous variation
- Chi-squared tests are used to determine whether the difference between an observed and expected frequency distribution is statistically significant
Applications:
- Morgan’s discovery of non-Mendelian ratios in Drosophila
- Completion and analysis of Punnett squares for dihybrid traits
- Polygenic traits such as human height may also be influenced by environmental factors
Skills:
- Calculation of the predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes
- Identification of recombinants in crosses involving two linked genes
- Use of a chi-squared test on data from dihybrid crosses