Question

Do you think that environmental factors also influence the sex determination in some

organisms? Support your answer by giving two examples.​

Answer 1

Environmental factors can sometimes play an important role in sex determination. Insects are not a special case—among the vertebrates, temperature also has a strong influence on sex determination in certain groups of reptiles. For example, in crocodilian reptiles and most turtles, sex is determined by egg incubation temperature. There are several variations on this theme. In the alligator snapping turtle, Macroclemys temminckii, incubation of eggs below 22°C or above 28°C gives rise to females, while incubation at intermediate temperatures produces predominantly males. American alligators show a similar biphasic dependence on temperature, but the curve is shifted to higher temperatures. In the European pond turtle, Trachemys scripta, incubation temperatures above 30°C produce all females, whereas incubation temperatures below 25°C produce all males. At 28.5°C, equal numbers of males and females are produced.

The temperature-dependent component of the sex-determination pathway has been studied in great detail in the European turtle, Emys orbicularis. In E. orbicularis, the critical temperature-dependent component appears to be synthesis of the enzyme aromatase, which converts androgens, such as testosterone, into estrogens. At higher temperatures, increased aromatase activity produces more estrogens, which biases the sex ratio toward more females.