Bio Exam


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This paper gives an explanation of Mendel’s theory of independent assortment. As well, the paper fully gives a description as to why a dihybrid cross that involves two LINKED genes with no crossing over approaches a 3:1 phenotypic ratio in the F2 generation. This has been supported by Gregor Mendel’s experiments which prove the law of inheritance, also known as the Mendel’s theory of independent assortment. This is a very important law which has been greatly adopted by students and teachers of genetics presently.

Mendel’s Theory of Independent Assortment

Gregor Mendel is known to be the father of heredity and came up with principles that govern heredity. His one outstanding principle is that of independent assortment which dictates that the allele pairs will separate in an independent manner during gamete formation. This is to say that the traits will be transmitted to the offspring in a manner which is independent on the other (Campbell et al 32). The major explanation behind the theory is that one allele tends to be dominant over the others, the hereditary units coming from the female and male will have to be blended within the genetic make-up of the offspring. The hereditary units influence a certain trait segregate during gamete formation. As well, each of the hereditary units tends to be inherited in a manner which is separate from all the hereditary units.

Phenotypic Ratio in the F2 Generation

With a dihybrid cross involving linkage of two genes which have no crossing over, a phenotypic ratio of 3:1 will be approaches in the F2 generation. From the Law of Independent Assortment, alleles from genes will assort in an independent manner during formation of the gametes. With Gregor Mendel’s experimental results, the mixing of dihybrid crosses gave 9:3:3:1 ratios (Hasan 27). However, with the 9:3:3:1 results, he was convinced that the two genes linked without any crossing over were inherited in an independent manner with a ratio of 3:1 without any kind of relation. In that case, while the phenotypic ratio would be 9:3:3:1, the phenotypic ratio would be 3:1 for each of the single traits. For example, color and length of the tail in a cat will be inherited in an independent manner. This was realized to be very true with any genes which are not in any way linked.

Works Cited

Campbell, Ballin., Mitchell, Lawrence, and Reece, G. Biology: Concepts and Connections. New York: Pearson Education, 2006.

Hasan, Heather. Mendel and the Laws of Genetics. New York: Rosen Publishing Group, 2005.


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