Autosomes and Allosomes


Autosomes are chromosomes apart from the sex chromosomes in a eukaryotic cell. In humans, the X and Y chromosomes are the sex chromosomes. All the chromosomes other than the sex chromosomes are autosomes.

There are 22 homologous pairs of autosomes in humans. Each autosome has several genes each of which performs certain unique functions. Different cell types in a eukaryote express a different combination of genes that enables cellular functions in eukaryotic organisms.


An allosome is a sex chromosome that differs in size, form and behaviour from an autosome. Humans have one pair of allosomes These chromosomes contain genes that determine the biological sex of an organism.

These chromosomes form pairs. The X and the Y chromosomes pair together during meiosis and this pair helps in sex determination.

Also Read: Determination of Sex

Difference between Autosomes and Allosomes

Following are the important differences between autosomes and allosomes:

Autosomes Allosomes
These determine the somatic traits. These determine the sex of an organism.
These are labelled with numbers 1 to 22. These are labelled with letters XY, XO, ZO, ZW.
There are same copies of autosomes in males and females. Allosomes difference in size, behaviour and form in males and females.
Most of the chromosomes in a genome are autosomes. Only a few chromosomes are allosomes.
It shows mendelian inheritance. It shows non-mendelian inheritance.
The pair of autosomes are homologous in humans. Female allosomes are homologous while male allosomes are non-homologous.
The number of genes varies from 200 to 2000. Y chromosome contains a few genes but X chromosome contains more than 300 genes.

Also Read: Genetics

For more information on autosomes and allosomes and the difference between the two, keep visiting BYJU’S website or download BYJU’S app for further reference.