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heredity and evolution — Science STD 10 — Question

Gujarat BoardEnglish MediumSTD 10Scienceheredity and evolution4 Marks
Question
Describe the sex determination in human beings.
✓

Answer

  • The sex determination in human beings is due to chromosomes and thus it is genetically determined.
  • Human beings have $23$ pairs of chromosomes.
  • Each pair has one maternal and one paternal copy.
  • $22$ pairs of chromosomes are similar in both male and female.
  • They are called autosomes, as they decide body characters.
  • $23$rd pair has sex chromosomes.
  • Women have a pair of $X$ chromosomes, i.e., females are therefore $XX$.
  • Men have a mismatched pair in which one is normal sized $X$ while the other is a short one called $Y$, i.e., Males are therefore $XY$.
  • As shown in figure, the probability of getting a male (boy) or a female (girl) child is $50 \%$.
  • All children will inherit an X-chromosome from their mother regardless of whether they are boys or girls.
  • Thus, the sex of the children will be determined by what they inherit from their father.
  • A child who inherits an X-chromosome from father will be girl and one who inherits a Y-chromosome from father will be a boy.

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