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Sex determination is an important topic in biology. It helps to know the sexual characteristics of organisms. So, we can know whether the offspring will be male or female. This technique is used to determine chromosomal sex. The male has the XY chromosome, which decides the gender. And the female has XX chromosome. In some animals, the temperature can decide the sex of offspring. They don’t need any genetic process. But in humans, the sex chromosomes of parents decide the gender of the child. So, let us know more details about sex determination in insects and Drosophila, sex determination in humans, sex chromosomes and the evolution of mammals.
Chromosomal Sex Determination
We need to know about the genetic makeup of human beings before knowing the sex determination in humans. There are 23 pairs of chromosomes in humans. It means a total of 46 chromosomes. The 22 pairs are called autosomes. And the one pair is called the sex chromosome. This pair helps to determine the sex of organisms.
It should be noted that this chromosome theory was first studied by the German scientist Hermann Henkingin in 1891. He found the different nuclear materials in the male gamete of insects. Then, he named it the X chromosome. Also, he found many insects have only one chromosome. It is denoted as XO. The study of sex determination in humans and birds has started.
Sex Determination in Insects
First, we know about sex determination in insects before knowing the sex determination in humans. It should be noted that animals that have two different sex chromosomes are called heterogametic sex organisms. They can produce two types of gametes. On the other hand, the animals have one type of chromosome called homogametic sex organisms. They can produce only one type of gamete.
Insects are a diverse class of organisms. They have dimorphic sex chromosomes. We can take the example of Lepidoptera. The female Lepidoptera has the W and Z chromosome. They are heterogametic. Whereas the male Lepidoptera has homogametic sex. Moreover, The W chromosome produces female characteristics. And when the W chromosome is absent, the ZZ chromosome produces male gametes, and ZO develops female gametes.
Sometimes the W chromosome has not developed female characteristics. Some insects, like moths, control their sex determination in temperature. When he finds a warm temperature, the Z chromosome is found on the inner spindle and develops in female eggs. On the other hand, when the temperature is cold, the Z chromosome moves to the outer pole and produces the male eggs.
Sex Determination in Birds
The sex determination in birds is different from the sex determination in humans. In the bird, Z and W are the sex chromosomes. The female birds have heterozygous sex. It is denoted as ZW chromosomes. And the male birds have homozygous sex, denoted as ZZ chromosomes. We can see this type of sex determination in birds, fishes and some insects.
Sex Determination in Human
As we know, females have XX sex chromosomes. The one X inherits from the mother, and the other X chromosomes inherit from the father. In contrast, males have XY chromosomes. The X chromosomes are inherited from the mother, and the Y chromosomes are inherited from the father. So, we can say that the father’s chromosomes are responsible for the gender of the children. His gamete can determine whether the offspring will be male or female.
In spermatogenesis in males, the gamete carries both the X and the Y chromosomes. So, when the fertilization takes place, the sex of the zygote will depend on the gamete of the male. Which gamete is fused with the X chromosome of the female? There are equal chances for a child to be a male or female. Thus, we understand the sex determination in humans. This sex determination has been going from the evolution of mammals.
Important point
Heterogametic:- The organisms that have two different sex chromosomes are called heterogametic. They produce two types of gametes.
Homogametic:- The organisms that have the only type of sex chromosome are called Homogametic. They produce one type of gametes.
Conclusion
We can understand sex determination in humans. It has been coming up in the evolution of mammals. Also, we understand the sex determination in birds and insects from the above. Now we understand when male XY gametes fuse with the X chromosome of the female. There are equal chances for a child to be a male or female. Because the sperm holds approximately 50 per cent of Y sperm cells and the other 50 per cent of X sperm cells, it should be noted that the pre-natal sex determination is an offence in many counties. The process of Amniocentesis can reveal the sex of the child in the womb. So, due to abortions of the female fetus, the government has banned sex determination of the unborn.
