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The Drosophila genes for white eyes (w), cut wings (ct), and tan body (t) lie at map positions 2.00, 15.0, and 21.0, respectively. Of 1000 progeny, 7 are double crossovers. What is the degree of interference

Sagot :

marianaegarciaperedo

Answer:

The coefficient of interference, I, is 0.1 (10% expressed as a percent)

Explanation:

Available data:

  • genes for white eyes (w), cut wings (ct), and tan body (t) lie at map positions 2.00, 15.0, and 21.0, respectively
  • Of 1000 progeny, 7 are double crossovers.

The coefficient of interference, I, is complementary with CC.

I = 1 - CC

To calculate the coefficient of coincidence, CC, we must use the next formula:

CC= observed double recombinant frequency/expected double recombinant frequency    

Note:  

  • observed double recombinant frequency=total number of observed double recombinant individuals/total number of individuals
  • expected double recombinant frequency: recombination frequency in region I x recombination frequency in region II.

By knowing the positions of genes, we can estimate the distances in MU between them per region.

  • The  distance between w and ct genes is 15 - 2 = 13 MU
  • The distance between ct and t genes is 21 - 15 = 6 MU

Now that we know the distances, we can estimate the recombination frequencies by dividing each distance by 100.

  • recombination frequency of w-ct region = 13MU / 100 = 0.13
  • recombination frequency of ct-t region = 6MU / 100 = 0.06

Now that we know the recombination frequencies in each region, we can calculate the expected double recombinant frequency, EDRF, like this:

EDRF = recombination frequency in region I x recombination frequency in region II.

EDRF = 0.13 x 0.06 = 0.0078

Now, by knowing the total number of individuals in the progeny (1000) and the number of double crossovers (7), we can calculate the observed double recombinant frequency, ODRF:

ODRF = number of double crossovers / total number of individuals

ODRF = 7/1000 = 0.007

Finally, with the values of EDRF and ODRF, we can calculate the coefficient of coincidence, CC.

CC = ODRF/EDRF

CC =  0.007 / 0.0078

CC = 0.9

And by knowing the CC we can also get the coefficient of interference, I.

I = 1 - CC

I = 1 - 0.9

I = 0.1 = 10% (expressed as a percent)

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