The determination of an individual’s sex varies among different species, and it can be influenced by either environmental cues or genetically determined factors. This phenomenon is known as sex determination, and the mechanisms can be diverse across the animal kingdom.

1) Genetically Determined: (Example: Mammals, Including Humans)
In mammals, including humans, sex determination is primarily genetically determined. The sex chromosomes play a crucial role. Females typically have two X chromosomes (XX), and males have one X and one Y chromosome (XY). The presence of the Y chromosome triggers the development of male characteristics. This genetic mechanism is conserved among many mammalian species.

Example: Birds:
In birds, the ZW system is used for sex determination. Females have a Z and a W chromosome (ZW), while males have two Z chromosomes (ZZ). The inheritance of the Z chromosome determines the development of male characteristics. This is an example of genetic sex determination in avian species.

2) Environmentally Influenced: (Example: Reptiles)
In reptiles, such as certain species of turtles and crocodiles, the sex of the offspring is influenced by the temperature at which the eggs are incubated. This is known as temperature-dependent sex determination (TSD). For example, in some turtle species, higher temperatures during incubation lead to the development of females, while lower temperatures lead to males. The specific temperature thresholds vary between species.

Example: Fish:
Some fish species exhibit environmental sex determination (ESD), where environmental factors, such as temperature, pH, or social conditions, influence the sex of the individuals. For instance, in some species of fish, the ratio of males to females in a population can be influenced by the water temperature during the early stages of development.

Example: Some Amphibians:
Certain amphibians, like frogs, also show environmental influences on sex determination. For some species, environmental factors, including temperature and humidity, can affect the development of male or female characteristics in the tadpoles.

In summary, we can say that – the mechanisms of sex determination vary across species. While many mammals, including humans, rely on genetic factors (chromosomal composition) to determine sex, other organisms, such as reptiles, fish, and amphibians, may be influenced by environmental cues like temperature. The diversity in sex determination strategies highlights the adaptability of different species to their environments and evolutionary pressures.