The differences between male and female sexes are anatomical and physiological. "Sex" tends to relate to biological differences. A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two sexes.
Types
XO type of sex determination
- Other than autosomes, at least one X chromosome is present in all insects.
- Some sperms contain X chromosomes, while some do not.
- Eggs fertilised by sperms having X chromosomes become females. So, females have two X chromosomes.
- Eggs fertilised by sperms not having X chromosomes become males. So, males have only one X chromosome.
- Example of organisms with XO type of sex determination − Insects
● XY type of sex determination
- Males have X chromosome and its counterpart Y chromosome, which is distinctly smaller. Hence, males are XY.
- Females have a pair of X chromosomes. Hence, females are XX.
- Example of organisms with XY type of sex determination − Humans and Drosophila
Male heterogamety − XO and XY types of sex determination are examples of male heterogamety.
- In XO type, some gametes have X chromosomes, while some gametes are without X chromosomes.
- In XY type, some gametes have X chromosomes, while some gametes have Y chromosomes.
Female heterogamety − ZW type of sex determination is an example of female heterogamety.
- In ZW type, the female has one Z and one W chromosome, while the male has a pair of Z chromosomes.
