3. Assume that crossing over does not occur in the region of each chromosome that is associated with the centromere

Question

3. Assume that crossing over does not occur in the region of each chromosome that is associated with the centromere. You have 46 centromeric regions in each cell, 23 that are copies of the DNA in your mother’s egg and 23 that are copies of the DNA father’s sperm.
a. For any given gamete, what is the probability that all the centromeric regions will be copies of the same ones that you received from your mother?
b. It has been estimated that the average person is heterozygous for at least 2,000 protein forming genes. How many different kinds of gametes is it theoretically possible for each person to produce?
c. Considering the maternal and paternal origin of the centromeric regions alone, how many different kinds of gametes can you produce?

Answer 1

a. The probability that all 23 centromeric regions in a given gamete will be copies of the ones received from the mother is approximately 1.19×10−71.19×10−7 (or 0.000000119%), which is a very low chance, indicating this is a rare event.

b. The number of different kinds of gametes it is theoretically possible for each person to produce, considering they are heterozygous for at least 2,000 protein-forming genes, is about 1.15×106031.15×10603. This is an astronomically high number, reflecting the vast genetic diversity possible in human reproduction.

c. Considering the maternal and paternal origin of the centromeric regions alone, you can produce 8,388,6088,388,608 (or 223223) different kinds of gametes. This number is still quite large and contributes significantly to the genetic variation seen in human offspring. ​​