Which one of the following is true regarding sex determination in human beings?

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Barr body is usually present in men and absent in women

If the first child of a couple is male, the probability of the second child to be female is 100%.

Sex of the child is determined by the genetic makeup of the sperm.

All the sperms have one set of autosomes and one Y-chromosome.

answer is C.

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Detailed Solution

During spermatogenesis among males, two types of gametes are produced. 50 percent of the total sperm produced carry the X-chromosome and the rest 50 percent have a Y-chromosome besides the autosomes. Females, however, produce only one type of ovum with an X-chromosome. In case the ovum fertilizes a sperm carrying X-chromosome, the zygote develops into a female (XX), and the fertilization of the ovum by a sperm carrying Y-chromosome results in male offspring (XY). Thus, it is evident that the genetic makeup of the sperm determines the sex of the child. The y chromosome has TDF(Testis Determining Factor) which determines the male sex. Its absence in zygotes leads to the female sex.

Barr's body represents inactivated X-chromosome. It is usually present in women but absent in men.

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