There are two primary differences between autosomal chromosomes and sex chromosomes:
- Autosomal chromosomes are not involved in sex determination, while sex chromosomes determine an individual’s biological sex.
- Individuals inherit autosomal chromosomes equally from both parents, while sex chromosomes are inherited differently depending on the sex of the parent.
In this article, we look at how autosomal and sex chromosomes carry out their varying functions, their evolution, and genetic disorders caused by abnormalities in these chromosomes.
Types of Chromosomes
Chromosomes, the thread-like structures made of DNA and proteins, contain thousands of genes that determine our physical and biological traits. However, not all chromosomes are the same. There are two main types of chromosomes — autosomal and sex chromosomes.
In humans, every cell contains 23 pairs of chromosomes. Out of this, twenty-two pairs are called autosomal chromosomes, while the 23rd pair — the sex chromosomes — determine the gender of the individual. {1}
Autosomal Chromosomes and Sex Chromosomes
Autosomal chromosomes are the 22 pairs of chromosomes that are not involved in sex determination. They contain genes that code for traits such as hair color, eye color, and height. Autosomal chromosomes are inherited equally from both parents, with one chromosome in each pair coming from each parent.
Sex chromosomes determine an individual’s biological sex. In females, the pair consists of two X chromosomes, while in males, the pair consists of one X chromosome and one Y chromosome. The presence of the Y chromosome determines male development, while the absence of it leads to female development.
Chromosomes and Genetic Inheritance
The DNA contains genes, which are the instructions for making proteins. During cell division, chromosomes are duplicated, and each new cell receives a copy of each chromosome.
In humans, the offspring inherits the genetic information from the parent and involves the fusion of their respective sex cells – a sperm cell from the father and an egg cell from the mother.
Each gamete contains half of the genetic information of the parent, which is called a haploid set of chromosomes.
The gender of the offspring depends on the inheritance of the sex chromosomes, which involves crossing over of the pseudoautosomal regions in these chromosomes.
How Do Autosomal Chromosomes Differ From Sex Chromosomes
The primary differences between autosomal and sex chromosomes are:
- Autosomal chromosomes are not involved in sex determination, while sex chromosomes determine an individual’s biological sex.
- Autosomal chromosomes are inherited equally from both parents, while sex chromosomes are inherited differently depending on the sex of the parent.
The Evolutionary History of Sex Chromosomes
Scientists believe that sex chromosomes originated from autosomal chromosomes, and evolved to become sex chromosomes over millions of years.
The process of sex chromosome evolution involves a series of genetic events such as gene duplication, gene loss, and recombination suppression. In most species, females have two identical sex chromosomes, while males have one X and one Y chromosome.
In many species, the Y chromosome has lost many of its genes over time, leading to a significant size difference between X and Y chromosomes, with the Y chromosome being smaller with fewer genes than the X chromosome. In some cases, the Y chromosome has even disappeared entirely, and sex determination is governed by other mechanisms.
For example, some species have evolved different systems for determining sex, such as the ZW system in birds, where females have a pair of sex chromosomes called ZW, while males have two copies of the Z chromosome and are ZZ.
Unlike the XY system found in mammals, where males have one X and one Y chromosome, it is the females in the ZW system that determine the sex of their offspring. Females can pass on either a Z or W chromosome to their offspring, while males can only pass on a Z chromosome.
The evolution of sex chromosomes is not yet fully understood, but scientists continue to study the process to better understand how it affects genetic diversity and species evolution.
Genetic Disorders Involving Autosomal and Sex Chromosomes
Both autosomal and sex chromosomes can be involved in genetic disorders. Autosomal genetic disorders include conditions such as cystic fibrosis and sickle cell anemia, while sex chromosome disorders include Turner syndrome and Klinefelter syndrome.
While the majority of individuals have two sex chromosomes that determine their biological sex, there are variations in chromosome number and structure that can affect gender development.
Frequently Asked Questions
Sources:
1 – National Human Genome Research Institute: “Chromosome.”
2 – National Health Services: “Klinefelter Syndrome.”