The sex of a newborn baby is determined by the chromosome inherited from

In humans, the sex of a newborn is determined by the sex chromosomes inherited from the parents. Females possess two X chromosomes (XX), meaning all eggs they produce carry an X chromosome [1]. Males possess one X and one Y chromosome (XY), resulting in two types of sperm: 50% carrying an X chromosome and 50% carrying a Y chromosome [1]. Since the mother always contributes an X chromosome, the sex of the child depends entirely on whether the father's sperm contributes an X or a Y chromosome [2]. If the sperm carries an X chromosome, the resulting XX combination produces a girl; if it carries a Y chromosome, the XY combination produces a boy [1]. Thus, the paternal chromosome is the deciding factor in sex determination [2].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 8: Heredity > 8.2.4 Sex Determination > p. 132
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 8: Heredity > What you have learnt > p. 133