A healthy couple with a history of three previous spontaneous abortions has just

Question

A healthy couple with a history of three previous spontaneous abortions has just had a child with cri-du-chat syndrome, a severe disorder in which the child makes a sound like a cat. The condition is associated with a deletion of the tip of chromosome 5. Their physician orders a karyotype analysis, which reveals the following structures for chromosomes 5 and 12 in the mother, the father, and the child. Are the chromosomes in the child consistent with those expected in a case of cri-du-chat syndrome? Explain your reasoning. Which parent has an abnormal karyotype? How can you tell? What is the nature of the abnormality? Why does this parent have a normal phenotype? Diagram the pairing of the abnormal chromosomes. What segregation pattern occurred to produce the gamete involved in fertilization of the child with cri-du-chat syndrome? What is the approximate probability that the next child of this couple will have cri-du-chat syndrome? Do the karyotypes of the parents help explain the occurrence of the three previous spontaneous abortions?

Explanation / Answer

a) The most common clinically significant chromosome abnormalities involving aneuploidy are frequently de-tected in newborns.

b) Although autosomal and sex chromosome trisomies result in clinical abnormalities they are more viable than monosomies, with the exception of monosomy X (45,X Turner syndrome). However, fewer than 5% of 45,X conceptions actually survive to birth.

c) Aneuploidy is frequently associated with maternal age and constitutes a significant portion of chromosome abnorm-alities observed in spontaneous abortions and detected prenatally in fetuses.

d)

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