ln human beings, the chromosomes that determine birth of a normal female child are ________.

In human beings, biological sex is determined by the inheritance of sex chromosomes. Humans typically possess 23 pairs of chromosomes, where the 23rd pair consists of sex chromosomes [5]. Females are characterized by an XX genotype, while males have an XY genotype [4]. During reproduction, a mother always contributes an X chromosome to her offspring because she only possesses X chromosomes [3]. The father, however, can contribute either an X or a Y chromosome via his sperm [6]. For a normal female child to be born, she must inherit one X chromosome from her mother and one X chromosome from her father, resulting in the XX pairing [1]. If the father contributes a Y chromosome instead, the child will be male (XY) [2]. Thus, the paternal contribution 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. [5] https://www.cdc.gov/fragile-x-syndrome/about/how-fragile-x-syndrome-is-inherited.html
3. [4] https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/genes-and-genetics
4. [3] https://www.genome.gov/27557513/the-y-chromosome-beyond-gender-determination
5. [6] https://www.ncbi.nlm.nih.gov/books/NBK9967/
6. [2] Science , class X (NCERT 2025 ed.) > Chapter 8: Heredity > What you have learnt > p. 133