A female of genotype produces 100 meiotic tetrads. 68 show no crossover events 2
ID: 56222 • Letter: A
Question
A female of genotype
produces 100 meiotic tetrads.
68 show no crossover events
20 show a crossover between a and b
10 show a crossover between b and c
2 show a double crossover between a and b and between b and c
Of the 400 gametes produced, how many of each of the eight different genotypes will be produced? (Hint: Recall that there are four chromatids in each tetrad and a single crossover involves only two of the four chromatids. Noninvolved chromatids must be added to the noncrossover classes.)
Label the diagram by dragging the labels to the appropriate targets. Note: not all labels will be used.
abc
+++
a++
+bc
++c
ab+
+b+
a+c
Explanation / Answer
Given below are the number of gametes of each type formed:
Genotype
No of gametes
a b c
136 + 20 + 10 + 2 = 168
+ + +
136 + 20 + 10 + 2 168
a + +
20
+ b c
20
a b +
10
+ + c
10
a + c
2
+ b +
2
b. The distance between a and b is 11 mu
c. The distance between b and c is 6 map units
Genotype
No of gametes
a b c
136 + 20 + 10 + 2 = 168
+ + +
136 + 20 + 10 + 2 168
a + +
20
+ b c
20
a b +
10
+ + c
10
a + c
2
+ b +
2
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