The inheritance rule was initially discovered by Mendel and it depends on clear
ID: 192234 • Letter: T
Question
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 Mendel’s law. Using obtained knowledge so far, what kind of cumulative effects would you add to this variation?
Explanation / Answer
Quantitative or additive inheritance is a type of non mendelian inheritance were the fate of a single trait is determined by more than one gene. Such a trait is called polygenic trait. For eg the single trait -human skin colour is determined by those genes involved in melanin production, and those genes involved in transport of melanin vesciles etc. Human height is also a polygenic trait.
In polygenic trait each gene product has a addictive individual effect, which can be summed up to the overall effect of the trait. That is why F1 generation has intermediate corolla length. Here dominace is either absent or there is partial dominance. The variation in F2 phenotype will be in continous range with the parents' phenotypes as their extreme limits on either ends, and each of these phenotypes depends on the number and nature of the genes involved.
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