Not all organisms have genetically determined sex. In some cases, the sex of an organism is determined by environmental factors or a combination of genetic and environmental factors. Here are two examples of organisms in which sex is not genetically determined:

1. Green sea turtles:
Green sea turtles (Chelonia mydas) exhibit temperature-dependent sex determination (TSD). The sex of the offspring is determined by the temperature at which the eggs are incubated. In this species, cooler temperatures (around 29°C) result in the development of male hatchlings, while warmer temperatures (around 33°C) lead to the development of female hatchlings. Intermediate temperatures produce a mixture of males and females. This phenomenon occurs because the temperature during incubation influences the action of certain enzymes involved in hormone synthesis, which subsequently affects the sexual differentiation of the embryos.

2. Clownfish:
Clownfish (Amphiprioninae) are another example of organisms with non-genetically determined sex. In clownfish colonies, there is a strict hierarchical social structure. They live in groups consisting of a dominant breeding female, a breeding male, and several non-breeding males. When the dominant female dies, the dominant male undergoes a sex change and becomes the new breeding female. The largest non-breeding male then transitions into a breeding male. This sequential hermaphroditism allows clownfish to maximize their reproductive success within their social group.

Both these examples highlight the significance of environmental factors in determining the sex of organisms. It demonstrates that sex determination is a complex process influenced by a combination of genetic and environmental cues. Understanding the mechanisms behind these non-genetically determined sex determination systems provides valuable insight into the diversity of reproductive strategies in nature.