Question

Discuss how sex in humans is determined

Answer 1

A baby’s sex is determined at the time of conception. When the baby is conceived, a chromosome from the sperm cell, either X or Y, fuses with the X chromosome in the egg cell, determining whether the baby will be female (XX) or male (XY).[5] To be female, one needs to be (XX), whereas to be a male, (XY) is needed. It is the Y chromosome that is essential for the development of the male reproductive organs, and with no Y chromosome, an embryo will develop into a female. This is because of the presence of the sex determining region of the Y chromosome, also known as the SRY gene.[6]

A fetus doesn't develop its external sexual organs until the second month of pregnancy—seven weeks after conception. The fetus appears to be sexually indifferent, looking neither like a male or a female. Over the next five weeks, the fetus begins producing hormones that cause its sex organs to grow into either male or female organs. This process is called sexual differentiation. The precursor of the internal female sex organs is called the Müllerian system.


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Answer 2

Answer:

(i) Sex determining mechanism in case of humans is XY type.

(ii) Out of 23 pairs of chromosomes present, 22 pairs  are exactly same in both males and females, these are autosomes.

(iii) A pair of X-chromosomes are present in the female.

(iv) Presence of X and Y chromosomes are determinant of male characteristic.

(v) During spermatogenesis among males, two types of gametes are produced. 50% carry X-chromosome and 50% has Y-chromosome besides autosomes.

(vi) Females produce only one type of ovum with an X-chromosome.

(vii) When ovum fertilises with a sperm carrying X-chromosome the zygote develops into a female (XX) and fertilisation of ovum with Y-chromosome carrying sperm results into male offspring.

(viii) Genetic make-up of the sperm determines the sex of the child.