Introduction to Sex Determination

Sex determination takes place with the help of genes inherited from parents. Particularly, genes are present on chromosomes in the nucleus of cell. Male and female gamete contains chromosomes. Fertilisation of these gametes, leads to the formation of zygote. The developement of zygote further gives rise to new individual.

“The biological process through which sexual characteristics of an individual develops making it a male individual or female individual is called sex determination.”

Sex determination in humans

• Normal human cells have 46 chromosomes or 23 pairs of chromosomes in the the nucleus. Out of 46 chromosomes, particularly one pair is of sex chromosomes. Sex chromosomes are named X and Y. In females, pair of sex chromosomes have both X chromosomes i.e XX pair, whereas, in males pair of sex chromosomes have X and Y chromosomes i.e. XY pair. In males as well as females, the gametes i.e. sperm or ova contains 23 chromosomes i.e half of total 46 chromosomes. More specifically male or female gamete contains single chromosome. Ova in females contains only X chromosomes, whereas, in males half sperms contain X chromosomes, and other half contains Y chromosomes.


Sex Determination

• At the time of fertilisation of male and female gamete, if sperm containing X chromosome fuse with ova containing X chromosomes, zygote formed after fertilisation contains XX pair of chromosome. Thus, zygote develop into female individual. However, during fertilisation if sperm containing Y chromosomes fuses with ova containing X chromosomes then zygote formed after fertilisation will contain XY pair of chromosomes. Hence, zygote will develop into a male individual





• Sex determination of child i.e. whether child is male or female completely depends on male parent rather than the female parent.

Environmental Sex Determination

• In loggerhead turtles sex can be determined on the basis of temperature in which the egg is developing. For example, if egg is developing at temperature 28℃ or below it then it produces male turtle. Also, if temperature is 30℃ and above then female turtle is produced.
• In case of snails, snails have ability to change their sex with respect to partner.

Keywords: Sex determination in humans, X chromosome, Y chromosome, XY chromosomes, XX chromosomes, Gametes, Fertilisation

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