Assume that there are 12 map units between two loci in the mouse and that you are able to microscopically observe meiotic chromosomes in this organism.If you examined 200 primary oocytes,in how many would you expect to see a chiasma between the two loci mentioned above?
A)96
B)48
C)6
D)12
E)24

Question

Quizplus · Accepted Answer

The frequency of chiasma formation between two loci is proportional to the distance between them. In this case, the distance is 12 map units. Therefore, the probability of a chiasma forming between the two loci is 12/100 or 0.12 (assuming one chiasma per meiosis).

For each oocyte, there is a 0.12 probability of a chiasma forming between the two loci. The probability of no chiasma forming is 0.88. Thus, the number of oocytes expected to have a chiasma between the two loci is:

200 x 0.12 = 24

However, since there are two homologous chromosomes, there are two chances for a chiasma to form between the two loci. Therefore, we must double the expected number of oocytes with a chiasma between the two loci:

24 x 2 = 48

Assume That There Are 12 Map Units Between Two Loci