The alleles for gene 1 are A and a The alleles for a second

The alleles for gene 1 are A and a. The alleles for a second gene are B and b. Crossing over between these two genes occurs 20% of the time. What is the corresponding recombination frequency? 10% 20% 30% 40% 50% What is the map distance between the two genes described in question 3? 10 m.u. 20 m.u. 30 m.u. 40 m.u. 50 m.u.

Solution

A crossing over of 20 % means exactly 20 chromosomes are recombinant for genetic markers flanking the cross over. In other words, 20 % crossing over corresponds to 10 % recombination because only half the chromatids in each cell with an exchange are actually recombinant. The frequency of recombination measures the intensity of linkage. When there is no linkage, the frequency is 50 % and when tightly linked, it is near zero. The recombination between two linked genes cannot exceed 50 % even when multiple crosses occur between them.

Question 3. Recombination frequency is 10 %.

The recombination ie crossing over tends to occur with increasing frequency as the distance between two specific gene loci increases. Hence the percentage of recombination (recombination frequency) can be used to represent map distance between the two genes. A crossing over or recombination of 1 % is equivalent to 1 map unit or centimorgan (cM). In humans, 1cM is roughly equivalent to 1 X 10 ⁶ basepairs (bps).

Question 4. Map distance between the genes A and B is 10 mu .