fertilization of an XX egg by a normal Y-bearing sperm
loss of half of the short arm of chromosome 5
loss of half of the long arm of chromosome 5
Solution
Cri-du-chat (cat's cry) syndrome, also known as 5p- (5p minus) syndrome is caused by a partial deletion (monosomy) of a varying length of the short arm (p) of chromosome 5. Infants with this condition often have a high-pitched cry that sounds like that of a cat. Down syndrome occurs due to trisomy of $21^{\text {st }}$ chromosome. Klinefelter syndrome is a genetic condition that results when a boy is born with an extra copy of the $\mathrm{X}$ chromosome.