BIO207H5 Lecture Notes - Lecture 21: Phenotype, Frequency Distribution, Inbreeding

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hassan_rizvi96

1 May 2019

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Document Summary

# additive genes proportional to number of phenotypic categories. If 2 genes 2(2) + 1 = 5. If a1a2 (1 gene) 2(1) + 1 = 3 categories. If a1a2b1b2 (2 genes) 4 +1 = 5 categories. If a1a2b1b2c1c2 (3 genes) 6 + 1 = 7 categories. 1 genotype more than 1 phenotype. Length based on segregation of alleles of multiple genes. Partially explains variation observed even in the pure-breeding lines. Crossing of pure breeding short and long corolla lines. Corolla length is intermediate between parents, with variance due to environment. Variance in corolla length is genetic and environmental. Three generations of selection for short and long corolla result in lines that resemble the parents. Different genotypes can produce similar phenotypes due to environment modulation. This is seen as there is an overlap between the phenotypes that are produced due to expression of genotypes. Construct a frequency distribution of values (proportion of individuals in each category)

Related Questions

The inheritance rule was initially discovered by Mendel and it depends on clear or qualitative traits. The theory was based on a single gene that was responsible for one character. However, expression of many traits are not governed by a single gene, rather can involve multiple genes as well as additive effects. This kind of inheritance pattern is known as quantitative and is demonstrated by East (1916) as well as others. He performed experiments using 2 homozygous, pure-breeding lines of Nicotiana longiflora that differed in corolla length. After crossing these lines, F1 offspring had an intermediate length for corolla and had same variation level as in parents. But found a very different result for F2 and F3 than expected. Discuss the reasons for this result and if it agrees/disagrees with Mendelâs law. Using obtained knowledge so far, what kind of cumulative effects would you add to this variation?