Question

The crossover frequency between the genes X and Z is 4%, Z and Y is 10%, X and Y is 6%. Find the sequence of genes on chromosome.

Answer 1

Answer:

Since, recombination frequency is directly proportional to distance between genes, the values are used to locate genes on a chromosome. Here, three genes a, b and c can assume any of three linear sequences : a-b-c or a-c-b or b-a-c which depends of the gene present in the middle. Here, recombination frequency for a and b (X) = 20%, that for a and c (Y) = 8% and for b and c (Z) =28%. As we can see that Z = X + Y or 28 = 20+8 which means that genes b and c are present at extremes and a is in the middle. Thus, the sequence of genes is b-a-c. Correct answer is B. For gene sequence a-b-c, Y = X+Z; but it does not hold true for given values of recombination frequency which makes option A wrong. For gene sequence a-c-b or b-c-a, X = Y + Z; but it does not hold true for given values of recombination frequency.

Answer 2

Answer:

Y-X-Z

Explanation:

• Recombination frequency is directly proportional to the distance between genes.
• Here, recombination frequency for X and Z [a] = 4% , Z and Y [b] = 10%    , X and Y [c] = 6%
• It can be observed that b = a+c , 10 = 6+4
• which means that genes Y and Z are present at extremes and X is in middle.
• Therefore, the sequence of genes is Y-X-Z.

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• Learn more about gene recombination frequency

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