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Sex determination in humans
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Which one of the following conditions of the zygotic cell would lead to the birth of a normal human female child?Humans have 23 pairs of chromosomes: 22 pairs of autosomes and one pair of sex chromosomes (2n = 46).
A normal female has the constitution 44 + XX and a normal male has 44 + XY.
The ovum always carries an X; if it is fertilised by an X-bearing sperm the zygote is XX and develops into a female child.
A zygote with one X and one Y develops into a male; only one X (XO) gives Turner's syndrome, a sterile abnormal female; a zygote with only a Y is not viable.
Hence a zygote with two X chromosomes leads to the birth of a normal female child.