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Principles of Inheritance and Variation — BIOLOGY STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 ScienceBIOLOGYPrinciples of Inheritance and Variation5 Marks
Question
How is sex determined in human beings?
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Answer

In human, XY type mechanism of sex determination is seen. There are 46 (=23 pairs) of chromosomes in humans of which 22 pairs are autosomes and are same in both male and female but 23rd pair is sex chromosome denoted as XX in female and XY in male. Therefore, the karyotype of male would be 44 + XY and that of female be 44 + XX.
From the study of Human karyotype, it is obvious that male is heterogametic and produces two types of gametes during of spermatogenesis:
(i) 50% of sperms contain X-chromosome and
(ii) Other 50% of sperms contain Y-chromosome Besides, the sperms also have autosomes.
There produces only one type of ova in female as she has sex chromosome XX. If sperm containing X-chromosome fuses with ovum, the zygote so developed contains XX and develops into female baby but if the sperm containing Y-chromosome fuses with ovum, the zygote so developed contains XY and develops as male child. It is therefore obvious that baby so conceived in each preganancy has the probability of 50% male/female baby.
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