Suppose that in Mendel’s pea plants, you are studying two genes, C and D, located close together on the same chromosome. You cross together a CCDD plant with a ccdd plant. The F1 plants have the genotype CcDd. This plant will make four gamete types, but most of them will be CD and cd types. Why will it not make similar numbers of the four gamete types? What is the mechanism that produces cD and Cd gametes?

Principle of independent assortment

Explanation:

Here the concept of independent assortment comes into the picture.

According to the principle of independent assortment, in a dyhybrid cross or mutiallelic cross the number of different type of allele associated with different genes sort separately in order to form gametes with one allele from each gene. Or in other way it can be said that the receiving of allele of one form with in a gamete is not affected by the receiving of allele for another gene.  

Hence, genotyoe CcDd will produce for gamete – CD, Cd, cD, cd

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