Assume that you are a genetic counselor and that a couple seeks genetic counseling from you. Both the man and the woman are phenotypically normal, but the woman is heterozygous for a pericentric inversion on chromosome 8. The man is karyotypically normal. What is the probability that this couple will produce a child with a genetic syndrome as the result of crossing over within the pericentric inversion

50%

Explanation:

An inversion is a genetic phenomenon that occurs when a chromosome breaks into two genomic sites, thereby the resulting DNA fragment is reversed and subsequently inserted into the same chromosome location. A pericentric inversion occurs when the chromosome breaks are located on opposite arms or sides of the chromosomal centromere. Moreover, crossing over (or recombination) is the exchange of genetic material between non-sister chromatids during gamete production. An inversion carrier, as in this case the woman who is heterozygous for a pericentric inversion, can produce four types of gametes. If there is no crossing over, half the chromatids will produce normal gametes (without the recombination event) and half the chromatids will produce balanced gametes that will transmit the pericentric inverted chromosome. On the other hand, if there is crossing over, half the chromatids will have one duplication on the first chromosome arm together with a deletion on the second chromosome arm, and the remaining half of the chromatids will have an inverse arrangement.

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