Question

What is the probability that, in an organism with a haploid number of 13, a sperm will be formed that contains all 13 chromosomes whose centromeres were derived from maternal homologs?

Answer 1

Answer is 0.00012.

Let us build a scenario to better understand the given problem. Let A (father) and B (mother) be the parents of C (male child). Now A will make two sets of sperm that will have 13 chromosomes each and similarly B will make two ovum that will have 13 chromosomes each. C will get 13 chromosomes from mother and 13 from father after a successful crossover. So the probability that a chromosome is from either A or B in C is 0.5. Now C makes his sperms, these are haploid cells containing 13 chromosomes. The probability that all the 13 chromosomes are from B will be given by the following product,

$\frac{1}{2} \times \frac{1}{2} \times \frac{1}{2} \times \frac{1}{2}.... \times \frac{1}{2}$ (13 times because there are 13 chromosomes in C's sperm)

Therefore the probability that C's sperm contain all maternal homologs is $(\frac{1}{2})^1^3 = 0.00012$.