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The Various Ways Species Determine Gender
by Shreya Dahal, age 13
 All over the world, plants and animals of different species from varied environments reproduce. One thing that is different across species is the mechanism that determines gender.
In all mammals, including humans, gender is determined by the X-Y system. Females have two X chromosomes while males have one X chromosome and one Y chromosome. The gender of offspring is determined by the sperm cell. If the sperm contributes a Y chromosome, male offspring is the result. If the sperm contributes an X chromosome, the offspring is female.
Birds are the opposite of humans in that their gender is determined by egg cells rather than sperm cells. The females are homozygous, having two identical sex chromosomes, whereas males are heterozygous, having two different sex chromosomes. These chromosomes are labeled W and Z.
Cockroaches and some species of grasshoppers determine the gender of their offspring in a different way. Only one type of chromosome exists: the X chromosome. A female has two X chromosomes, while a male has only one. The gender of offspring is determined by whether or not the male passes on his chromosome. If he does not, the offspring is male.
In many other animals, chromosomes do not determine gender. For example, crocodile and turtle offspring gender depends on the egg temperature during incubation. If the egg is incubated in high temperatures, the offspring is female. If it is incubated in low temperatures, then it is male.
Unlike most other living things, most plants are hermaphroditic, meaning that they have both male and female sex organs.
For some plant species, genetic makeup determines gender; for others, environment plays a central role.
[Source: Science Illustrated]
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