Question

In most of the higher unisexual animals there is one chromosomal pair that is not identical in two sexes. These are called
(a) Non-homologous chromosomes
(b) Non-identical chromosomes
(c) Non-compatible chromosomes
(d) Sex chromosomes

Answer 1

These chromosomes are known by different names such as allosomes, heterochromosomes, or isochromosomes. These chromosomes also vary from a normal autosome in structure, size, and behaviour.

Complete Step by Step Answer:
In both sexes, sex chromosomes vary in higher animals. Let's take the example of human beings, where men have XY (sex chromosomes) where on the other hand women have XX (sex chromosomes).
The sex chromosome determines the sex of an organism which are created by sexual reproduction. The process of sex determination varies among groups.
So, the answer is ‘Sex chromosomes’.

Additional information:
- Every cell nucleus of human beings contains 23 pairs of chromosomes, which makes a total of 46 chromosomes. Among them, the first 22 pairs are known as autosomes.
- Autosomes are also called as homologous chromosomes, but the chromosomes of the 23rd pair consist of two X chromosomes in men and one X chromosome and Y chromosome in the men
- Due to this women have 23 homologous chromosome pairs and men have only 22. In the ovum, the X chromosome is constantly depicted as the 23rd chromosome and in a sperm cell, either an X or a Y chromosome can be present.

Note:
- In rare conditions, some humans have a different sexual development known as the intersex which can be due to an allosome which is neither XX nor XY.
- In some organisms, the sex determination is by environmental factors, for example, the sex determination in reptiles is depended on the incubation temperature, and in some fishes and amphibians it is influenced by the temperature of the surrounding water
- Another rare condition exists where females have three X chromosomes, which is known as the superwomen condition, where the individuals express over feminine conditions.