Mechanism of Heredity Transmission - Sex Determination

Sex determination means how the baby’s gender (boy or girl) is decided when the egg from the mother meets the sperm from the father.

• Each parent has 23 pairs of chromosomes.
• One pair is called “sex chromosomes”.
• Females have two X chromosomes (XX).
• Males have one X and one Y chromosome (XY).

• The mother's egg always has an X chromosome.
• The father's sperm can have either an X or a Y chromosome.
• If the sperm with an X joins the egg (X+X), the baby is a girl (XX).
• If the sperm with a Y joins the egg (X+Y), the baby is a boy (XY).
• Half of the father's sperm have X, half have Y. So, the chances of having a boy or a girl are equal.

• Y sperms are lighter and sometimes swim faster, so a few more boys might be born than girls.
• Before conception, it is not possible to predict the child’s sex.
• The common belief that the mother decides the child's sex is incorrect.

• Girl: X from mother + X from father.
• Boy: X from mother + Y from father.
• Chances are the same for both.
• The father’s sperm decides the sex.