What are Autosomes? Definition, Meaning, Genes, Inheritance and Disorders

What are Autosomes? Definition, Meaning, Genes, Inheritance and Disorders

“Autosomes are the 22 pairs of human chromosomes other than the sex chromosomes.” 


All the DNA or genetic material of a cell is located on chromosomes which is the highest level of organization of DNA. 

The DNA is located on chromosomes to fit inside the cell and to replicate properly. The set of proteins known as the histone proteins help them to do so. 

Chromosomes are present in a pair; 23 pairs of chromosomes are present in the human genome, however, the numbers of chromosomes are different in different species. 

DNA is a larger molecule in terms of length; one study revealed that we can go to the sun and return to earth if we unwind all the DNA of all the bodily cells.
Therefore it is very important for DNA to arrange compactly to fit inside a cell. By tailoring a structure known as chromosomes, DNA achieves a higher level of organization. 

In the present article, we will discuss the autosomes, genes located on autosomes and autosomal disorders. We will also discuss how autosomal genes are inherited. 

Read more: Chromosome- Definition, Structure, Function And Classification.

What are autosomes? 

Every chromosome has an identical copy, for instant 1 and 1, 2 and 2 and so on. A single set of chromosomes are known as haploid while a pair of two sets is known as diploid or (2n). 

One set of chromosomes comes from the father and another from the mother and that makes a whole diploid genome. Broadly, the chromosomes are divided into two categories sex chromosomes and autosomes. 

The sex chromosomes are either XX or XY in females and males respectively. We can say X and Y are the sex chromosomes in humans, noteworthy it is also present in other mammals as well. It is also known as allosomes. In some other organisms, it is denoted differently

For example, birds have ZW chromosomes as their sex chromosomes. The rest of the pairs are known as autosomes. 

The allosomes are different from the autosomes because they are not always present in the same pair, for example in males it is XY. But the autosomal pairs remain the same.

The pictorial representation of 22 pairs of autosomes.
The pictorial representation of 22 pairs of autosomes.

Meaning of autosomes: 

The word ‘autosome’ is used for a specific group of chromosomes. ‘Chroma’ means ‘color’ and ‘soma’ means ‘body’.

The term autosome was derived from the Ancient Greek word chromosome whose portion, ‘soma’ means ‘body’. It literally means “soma” or chromosomes other than sex chromosomes. 

A pair of sex chromosomes majorly work for in sex differentiation and sex determination and that is the functional difference between autosomes and allosomes.

However, other autosomal genes are also involved in that process. And note that other genes related to mental development and cognitive development are located on either X or Y chromosomes too. 

Related article: Prokaryotic Chromosome- Definition, Structure and Function.

Definitions:

Chromosome sets other than the allosomes or sex chromosomes, having present in an identical pair and containing a major portion of the genome is known as the autosomes. 

Read more: Definition Of Genetics And Related Terminologies.

Structure: 

Structurally, though the autosomes are different from the allosome, even not all the autosomes are similar. 

Much like other chromosomes autosomes have centromere, arms and telomere. 

Based on the location of the centromere, and the size of the chromosomes, it is categorized into metacentric, submetacentric, acrocentric and telocentric. See the table below, 

The chart of various categories of human chromosomes based on their centromere location.
The chart of various categories of human chromosomes based on their centromere location.

Note that genes are located on the arms of chromosomes. 

List of autosomes: 

Autosome Size Important genes 
1249Mb MTHFR, JAK1, RSPO1 and TAL1
2243MbNCL, AGXT and TTN
3200MbSOX2, and ZNF9
4190MbHTT, Factor XI and complement factor I
5180MbIK and SMN1
6170MbHLA-A, B and C
7159MbBRAT1 and SCIN
8146MbZNF16, TG and TGFR1
9140MbGALT, ABO and INSL6
10135MbPTEN, GATA3 and RET
11134MbHBB, insulin and WT1
12132MbOAH, MYO1A and KRAS
13114MbBRCA2, BRCA3, TB1 and POMP
14107MbGALC, PSEN and ACIN1
1581MbHEXA and OCA2
1690MbNOB1, TELO2 and ZNF200
1783MbHN1, STH and BRCA1P1
1878MbPIGN, DCC and ESCO1
1959MbHRC
2063MbJAG1 and ADA
2148MbBCR, MN1 and COMT
2251MbTRO, APO and GATA1

Functions: 

Like other chromosomes, the autosomes are responsible for the inheritance of genes. Actually speaking, the function of chromosomes is not only to inherit genes but also to make DNA fit inside a cell. 

Autosomes are the network of protein and genes that actually helps DNA to settle in the nucleus of a cell, afterward, transmits genes to other cells. 

Genes located on the autosomes are known as autosomal genes.

Approximately, 80% of protein-coding genes are located only on autosomes, which are responsible for the proper functioning of the brain, muscles, reproductive system, nerve system, cellular activities, catalytic reactions, metabolic pathways and many more. 

The function of top genes located on autosomes: 

MTHFR gene

The MTHFR gene is an autosomal gene located on chromosome 1. It is a candidate gene involved in the metabolism of folate or folic acid. 

Mutation in MTHFR can cause several abnormalities majorly associated with the folate metabolism such as hyperhomocysteinemia, recurrent miscarriage, schizophrenia, infertility and other mental and developmental conditions. 

Two candidate gene mutations of the MTHFR are C677T and A1298C. 

Read more on a related topic: Genetics of MTHFR: Gene, Mutations, Variants, Inheritance and Testing.

JAK1 gene

Another autosomal gene situated on chromosome 1 is the JAK1 that is a tyrosine kinase gene. The JAK1 gene encodes a protein tyrosine kinase which is mainly involved in the pathways of the immune system. 

Mutation in the JAK1 gene can cause various types of cancer. Some are lethal as well. 

ZNF gene family: 

Genes of the ZNF family which encodes mainly zinc finger proteins are located on various autosomes. They are supposed to be involved in cellular, developmental and other metabolic pathways. 

HLA gene family: 

Human leukocyte antigen gene families are the class of genes involved in manufacturing human leukocyte antigen and are located on chromosome 6- autosome, again. 

HLA are key components of the immune system, the major portion of the p-arm of chromosome 6 is the HLA gene-rich region often known as the HLA gene cloud.  

It provides antigen diversity to different individuals and therefore very important for a person. 

The HLA gene cloud is also used by a maker to perform a test for organ donation. 

PTEN gene: 

The PTEN gene is located on chromosome 10- an autosome manufactures an enzyme phosphatase and tensin homolog. It is a tumor suppressor gene that helps in controlling the process of apoptosis. 

Mutation in the PTEN gene can cause several types of cancers. 

HBB gene: 

Yet another important autosomal gene is located on chromosome 11 in the HBB gene. The HBB gene is the human beta-globin gene that helps in manufacturing the beta-globin chain of the hemoglobin. 

Their main role is to transport oxygen through blood in various parts of the body. Mutations in the HBB gene can either anemia, mainly sickle cell anemia or thalassemia. 

Related article: Sickle Cell Anaemia: Definition, Cause, Genetics, Trait, Symptoms and Diagnosis.

BRCA gene: 

The gene responsible for hereditary breast cancer- BRCA2 is located on autosome 13. It is responsible for a severe type of breast cancer. 

Besides, SOX3, SOX9, RSP0, DCC, HN1, RB1, KRAS, GATA3 are located on autosomal chromosomes involved in cell differentiation, sex differentiation and determination, cognitive development, and mental development. 

Read more: Breast Cancer Genetics- Genes, Mutations, Inheritance, Testing and Diagnosis.

Some of the functions of autosomal genes are;

  • Cell differentiation
  • Cell death 
  • Cell metabolism, 
  • Development of blood cell
  • Cognitive development 
  • Mental development 
  • Sex determination and differentiation 
  • Fetal development 
  • Muscle development 
  • Blood system- hemoglobin, blood clotting, blood cell formation, etc 
  • Formation, synthesis and metabolism of the nerve system and related components 
  • Immune system and related components 
  • Cell metabolism

The inheritance pattern of autosomes: 

The autosomes follow a distinct and unique inheritance pattern, different from the X or Y chromosome. 

Autosomal genes follow either autosomal dominant or autosomal recessive inheritance pattern which is similar in all, unlike the sex chromosomes. 

In an autosomal dominant inheritance, a single autosomal gene is enough to show phenotype while in autosomal recessive inheritance, two recessive alleles contribute to manufacturing a phenotype. 

Take a look at some of the examples of autosomal disorders;

List of autosomal recessive disorders: 

Number Autosomal recessive disorder 
1Cystic fibrosis 
2Sickle cell anemia 
3Beta-thalassemia 
4Tay-Sachs disease 
5Congenital adrenal hyperplasia 
6Ataxia telangiectasia
7Friedreich’s ataxia 
8Gaucher’s disease 
9Glycogen storage disorder 
10Phenylketonuria 
11Hurler’s syndrome 
12Wilson’s disease 
13Oculocutaneous Albinism
14Deafness 
15Fanconi syndrome 
16Galactosemia 
17Homocystinuria 
18Infantile polycystic kidney disease 
19Galactosaemia 
20Crigler-Najjar syndrome type I

List of autosomal dominant disorders  

1Neurofibromatosis type 1
2Marfan syndrome 
3Huntington’s disease 
4Myotonic Dystrophy 
5Achondroplasia 
6Polycystic kidney 
7Von Willebrand disease 
8Osteogenesis imperfecta 
9Familial hypercholesterolemia 
10Familial adenomatous polyposis 
11Hypertrophic cardiomyopathy 
12Tuberous sclerosis 
13Hereditary hemorrhagic telangiectasia 
14Hereditary non-polyposis coli 
15Noonan syndrome 

Autosomal genetic disorders: 

Due to various reasons- changes in the structure of the number of autosomes can cause genetic disorders if arise from birth known as birth defects or congenital birth defects

Several common autosomal disorders are discussed here: 

Aneuploidies: 

Either increase or decrease in chromosome number is categorized into aneuploidy, trisomy is one of the common types of it. Trisomy 13, 18 and 21 are the most prevalent aneuploidy of autosomes. 

Trisomy 13, 18 and 21 are known as Patau syndrome, Edward’s syndrome and Down syndrome, respectively. All three are the type of numerical chromosomal abnormalities in which an extra copy of chromosomes 13, 18 and 21 are observed with a pair. 

A type of autosomal chromosomal abnormalities, trisomies, occurred by an event known as nondisjunction during cell division. 

Broadly, this causes structural, developmental, reproductive, cognitive and mental problems in the patient. 

Related articles:

  1. Down syndrome- trisomy 21
  2. Patau syndrome- trisomy 13
  3. Edward’s syndrome- trisomy 18

Translocation: 

When a portion of a chromosome translocates to another chromosome, it is known as translocation. One of the most common types of translocation is between 22 and 9, known as the Philadelphia chromosome

It causes a type of cancer, chronic myeloid leukemia which has a definite inheritance.

Deletion: 

The deletion occurs when a part of the chromosome got deleted or missed. Cri-du-chat is one of the most common deletion syndromes. In the present condition, a part of chromosome 5, the portion of the p-arm of the chromosome is deleted. 

To know more about deletion syndrome you can read this article: What is Deletion Syndrome? Top 6 Chromosomal Deletion Syndromes Explained.

Autosome and gene expression:

The expression of a gene matters a lot in order to produce a complete trait or phenotype. Gene expression is defined as the amount of mRNA produced from a gene. 

The total genetic content of an autosome should be expressed in a particular amount. Copy number variations changes in gene expression in which some portions of autosomes are deleted or duplicated. Here, deletion or duplications may contain a gene or a few genes or many genes that consequences in altered gene expression. 

Change in the expression of autosomal genes may cause altered, over or under-expression of genes that produce faulty or abnormal protein products. 

If a portion of any of the autosomes got deleted or duplicated it adversely influenced gene expression profile. 

DNA microarray is a great tool to study the expression of genes (thousands of genes) of either autosomes or all chromosomes in a single run. 

Conclusion:

The major portion of our genome is made up of autosomes. And hence they contain 95% of the important genes to perform various functions. Nonetheless, sex chromosomes and autosomes are equally important.


Sources:

Haig D. A brief history of human autosomes. Philos Trans R Soc Lond B Biol Sci. 1999 Aug 29;354(1388):1447-70. doi: 10.1098/rstb.1999.0490.

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