A female has the following genotype: This female produces 100 meiotic tetrads. O

Question

A female has the following genotype:

This female produces 100 meiotic tetrads. Of these, 68 show no crossover events. Of the remaining 32, 20 show a crossover between a and b, 10 show a crossover between b and c, and 2 show a double crossover between a and b and between b and c.

Assuming the order a-b-c and the allele arrangement shown above, what is the map distance between a and b loci?

Assuming the order a-b-c and the allele arrangement shown above, what is the map distance between b and c loci?

Explanation / Answer

68 are parental, that means no crossing over takes place.

32 recombinant individuals. They contain both Single Cross Overs (SCO) & double Cross overs (DCO).

Progeny produced by Cross over between a & b = 20

Progeny produced by Cross over between b & c = 10

DCO = 2

Distance between a and b = progeny of a and b cross over + DCO / Total Progeny

20 + 2 / 100

= 22/100

22%

So a and b distance = 22 map units

Similarly b and c distance = 12 map units

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