Bookmarked! 1.In tribbles (a fictional creature inhabiting the world of star tre

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1.In tribbles (a fictional creature inhabiting the world of star trek), the dominant gene B gives black fur, whereas b gives brown (chocolate). On other chromosome, the gene E is also involved in fur color. A breeder wants to determine the genotypes of three of his tribbles, so he interbreeds them over several weeks. The data are in the table below.
Question Details
other breeder have done dihybrid crosses and found that black crossed with black gives yellow:black:chocolate in a 12:3:1 ratio.

Cross Phenotype Progeny
1 tribble 1 (yellow) x tribble 2 (yellow) 6/8 yellow
1/8 black
1/8 chocolate

2 tribble 1 x tribble 3 (black) 4/8 yellow
3/8 black
1/8 chocolate

A. What are the genotype of the breeder's three tribbles? Explain your reasoning.

B. what type of dyhybrid interaction is occurring between the B locus and the E locus? Use the information given above. Be specific and explain your reasoning.

C. What is the genotype of a chocolate tribbles?

Explanation / Answer

A. the first genotype question is referring to a dihybrid cross of the dominant gene E which allows no color expression or yellow, and e for color expression, as well as the sub-gene B for black and b for chocolate. in the G generation,the cross involves two tribbles that are heterozygous for the E gene as well as the B gene... their genotypes are as follows... (Tribble 1)-EeBb (Tribble 2)-EeBb (Tribble 3)-eeBb or eeBB B. Now specifically, when one gene regulates the expression of another gene it is known as an epistatic interaction. In this case when you conveniently have two heterozygous breeders, the interaction is illustrated by the correlation of genotypic expressions in the secondary affected gene. In the case of an epistatic gene that allows color when dominant, the genotypic ratio will be expressed as a 12:3:1 as it is in this case... hence the validation of the hypothesis that the first two tribbles are heterozygotes for both traits. C. The Genotype of a chocolate tribble is still dictated by the epistatic gene E in this case so the third tribble would need to have the reccessive gene for color, which in this case is e.But it cannot be determined weather or not the secondary affected gene is homozygous or heterozygous, unless further genetic tests or breeding is done with the third tribble. Therefore the third tribbles genotype is either eeBb or eeBB.

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