Questions from inside the book

Class 10
Chapter 9 Class 10 - Heredity and Evolution

## How is the sex of the child determined in human beings?

Human beings give birth to male and female children due to genetic reasons

• Human beings have 46 chromosomes (23 pairs of chromosomes)
• Out of the 23 pairs, 22 pairs (44 chromosomes) each have a copy from the mother and father .
• The Remaining 1 pair is called the sex chromosome. It is what determines the sex of the child.
• Women have a perfect pair - both are X - XX (Egg)
• Men have one normal sized X chromosome and another short chromosome called Y chromosome - XY (Sperm)
• The sex of the offspring is dependant upon which chromosome is copied from the father (X or Y) and hence forms the genetic material of the offspring.
• If the X chromosome is copied , it combines with the X from the mother to form a biologically female (XX) Egg . If the Y chromosome is copied , it combines with the X chromosome from the mother to form a biologically male (XY) egg .
• So,

• This means that there is a 50% chance that the child is a male or female.
• Though the sex is determined by which gene is inherited from the father , the process in completely by chance and the probability of the child being male or female is equal.

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