S6. Assume that a rescarcher is studying coat color in voles, \'Three strains of
ID: 270471 • Letter: S
Question
S6. Assume that a rescarcher is studying coat color in voles, 'Three strains of white vole have been isolated: milky, blanc, and weiss. White is a recessive trait in each strain Homoaygous white voles are obtained for each strain. Consider the following crosses milky × blanc = all white progeny mailly x weiss all brown (wild-type vole color) blanc x wess = all brown (wild-type vole color) The conclusion most consistent with these results is: A) all three strains have mutations in the same gene. B) all three strains have mutations in different genes C milky and blanc have inutations in the same genc, weiss has a D) milky and weiss have mutations in the same gene, blanc has a mutation in a different gene. mutation in a different gene E) weiss and blanc have mutations on the same gene, milky has a mutation in a different gene. 57. Assume 8 different pure-breeding strains of fly have been isolated and each shows a recessive white eye cross is tabulated below. (w) indicates white-eyed progeny, (R) indicates wild-type red eyes wR Rw w R Based on these crosses, how many different genes are present and which strains have mutations in the same strain A? gene a A) 2; B, E, and H B)3; B,and C C)3 B,C, and H D) 3; B, E, and H E 4; B, and HExplanation / Answer
56. C.
White coat colour will be expressed only when alleles are present as homozygous pair. Consider M,B and W to be dominant alleles for milky, blanc and weiss colours. Since they are all strains of white voles, let's say they are all in heterozygous combination, such that:
Mw x Bw = all white
Mw x Ww = all brown (wild-type)
Bw x Ww = all brown (wild-type)
Since we get wild-type in the second and third crosses, it is to be assumed that one amongst M, W and B is dominant. W which appears in both is dominant. However, going by the results of these crosses, all cross will have ww which should code for white coat colour. Since that doesnt happen, and because W is found dominant, there is a chance that another gene which exhibits co-dominance is with W, say WW'. In this case, we will have second and third crosses having MW,MW',Ww (2), W'w(2), BW and BW' as the offsprings, where W and W' dominance causes all to be in brown coat colour.
Given this case, milky and blanc has mutations in the same gene, which is different from the gene mutated for weiss coat colour.
57. A.
In the table above, AA, AB, AE, AH, BB, BE and BH all gives w. Therefore, strains with mutation similar to A is B,E and H. This can be proved by randomly selecting crosses of these with any strain, the result will appear to be same in all cases, say for example AF, BF, EF and HF will all code for R.
Only 2 genes are present, because there's no intermediate trait that is considered. Heterozygous dominance and homozygous dominance will code for wild type and homozygous recessive for mutant white eye.
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