(2 points) You are trying to map several genes that you know are close together
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(2 points) You are trying to map several genes that you know are close together on the chromosome. To map means to figure out which order they are in on the chromosome. In your diploid model organism, one copy of the chromosome has all normal, dominant alleles of these genes. It is A B C D E F. But the other copy of the chromosome has all recessive alleles, a bcdef. So overall, the organism has the dominant phenotype for each gene. Please recall that the genes lie always in the same order on both only difference is that the recessive romosomes; the ones are mutated Now, if you delete a chunk of the dominant chromosome, containing some of the dominant genes, you will have a recessive phenotype for those genes, since the only copies left are recessive. Here are the chunks you delete and the resulting phenotypes. From this data: You delete a chunk of the "dominant chromosome" and get recessive phenotypes for d, b, ande Starting from scratch, you delete a different chunk of the "dominant chromosome" and get recessive phenotypes for e and f, Again starting from scratch, you delete a different chunk of the "dominant chromosome" and get recessive phenotypes for b and c Finally, starting again from scratch, you delete a different chunk of the "dominant chromosome" and get recessive phenotypes for a, c, and b Figure out the order of the genes.Explanation / Answer
Our diploid organism has the normal dominant alleles ABCDEF on one copy of c chromosome and mutated recessive alleles abcdef on the other copy.
Now, when one deletes a chunk of the dominant chromosome, certain dominant alleles are lost, resulting in a recessive phenotype. It is safe to assume, that when a 'chunk' of the dominant chromosome is deleted, genes lying close to each other on that chunk will be deleted. It is known that genes always lie in the same order on both the chromosomes in a pair.
Now, in the first deletion, the dominant alleles D,B and E are lost. That means, D,B and E are close to each other. However, their order is still not known. Let us write it as (D-B-E). Alleles separated by dashes and written in a bracket indicates that they are close to each other, but their order is not known.
In the second deletion, the dominant alleles E and F are lost.That means, E and F are close to each other. Thus, we have (E-F).
In the third deletion, the dominant alleles B and C are lost. (B-C).
In the final deletion, the dominant alleles A, C and B are lost. (A-C-B).
Now, one can see that in some deletions,some common alleles have been lost. For example, E is the dominant allele lost in both the first and the second deletion. Let us use these overlaps to map the chromosome.
Thus, what we have till now is
(D-B-E)
(E-F)
(B-C)
(A-C-B)
Since the first deletion removes D,B and E, and the second deletion removes E and F, we can safely assume that the alleles D and B and the allele F lie on opposite sides of E. This is based on our assumption that alleles lost in a deleton are close to each other. Let us write them as (D-B)>E>F.
Similarly, from the third and fourth deletions, we get A>C>B. These two findings tell us that the alleles C and B are consecutively placed. That means, the allele D does not lie between C and B. Thus, from all these findings, we come to the conclusion, that the order of these genes is A>C>B>D>E>F.
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