Crossing over within a pericentric inversion produces chromosomes that have extr
ID: 227065 • Letter: C
Question
Crossing over within a pericentric inversion produces chromosomes that have extra copies of some genes and no copies of other genes...
Map Genetics: A Conceptual Approach 6th Edition MHE/Freeman presented by Sapling Learning Crossing over within a pericentric inversion produces chromosomes that have extra copies of some genes and no copies of other genes. The fertilization of gametes containing these duplication or deficient chromosomes often results in children with syndromes characterized by developmental delay, mental retardation, abnormal development of organ systems, and early death. One study examined individual sperm cells of a male who was heterozygous for a pericentric inversion on chromosome 8 and determined that crossing over took place within the pericentric inversion in 26% of the meiotic divisions. Assume that a man and a 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's child will inherit a duplicated or deficient chromosome 8that results from crossing over within this pericentric inversion? Number Jaarola, M. Martin, RH, Ashley, T. Direct evidence for suppression of recombination within two pericentric inversions in humans: a new sperm-FISH technique Am J Hum Genet, 1998, 63, 218-224.Explanation / Answer
There are two independent events: first normal and second is inversion. The probability of inversion is 26% or 0.26. Therefore, the probability of non-inversion is =1- 0.26 = 0.74. Now we suppose the inversion occur then the cross between father and mother would give the result as given below.
Father AA x Mother Aa [where A is normal and a is inverted allele]
Gametes
A
a
A
AA
Aa
There is one child affected by mutation between two children. Therefore the probability of affection is 50% or 0.5 [1/2=0.5]. However, from the above inversion probability the overall probability of having affected child is as below.
=The probability of inversion x probability of having disease
=0.26 x 0.5 = 0.13.
Therefore, the probability of having affected child =0.13 or 13%
Gametes
A
a
A
AA
Aa
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