What are Autosomes and Allosomes? – Difference and Functions

Autosomes and Allosomes are two types of chromosomes found in the cells of living organisms, particularly in sexually reproducing species. Autosomes chromosomes are somatic chromosomes that determine an organism’s physical characteristics and allosome chromosomes are sex chromosomes that determine an organism’s sex and sex-linked inheritance. In this article, we will discuss the Autosomes and Allosomes chromosomes – characteristics, their functions, and the differences between Autosomes and Allosomes.

What are Chromosomes?

Chromosomes are thread-like structures that carry genetic information from cell to cell. Chromosomes is made up of DNA that is tightly coiled around proteins called histones. The DNA is further condensed by winding around itself to form chromatin. Chromosomes carry information about the organism in units called genes. When living things reproduce, they pass their genes along to their offspring.

Humans have 23 pairs of chromosomes, which are of two types: Autosomes and Allosomes. Autosomes are the 22 pairs of numbered chromosomes, while allosomes are the one pair of sex chromosomes. Autosomes contain information about heredity, while sex chromosomes determine the sex of the next generation.

Also Read: How is the Sex of the Baby Determined?

What are Autosomes?

Autosomes definition states that they are somatic chromosomes responsible for general traits. They are found in the nucleus of the eukaryotic cells. Humans have 23 pairs of chromosomes, including 22 pairs of autosomes and one pair of allosomes. Autosomes chromosomes show Mendelian inheritance and can be part of both haploid and diploid cells. 

In humans, body cells are diploid and have two sets of autosomes, one from each parent. Autosomal recessive inheritance occurs when a trait is expressed only if an individual inherits two copies of the recessive allele, one from each parent. Autosomes contain sexual determination genes even though they are not sex chromosomes. For example, the SRY gene on the Y chromosome encodes the transcription factor TDF and is vital for male sex determination during development.

Also Read: Difference Between Chromatin And Chromosomes

What are Allosomes?

Allosomes, also known as sex chromosomes or heterosomes, are a pair of chromosomes that determine a person’s gender. In humans, the 23rd pair of chromosomes are allosomes. In females, allosomes are XX, while in males, allosomes are XY. Females have 23 homologous chromosome pairs, while males have 22. Allosomes chromosomes show non-mendelian inheritance and are different from autosomes in size, shape, and function. Together Autosomes and Allosomes determine the chromosomal makeup of a diploid organism.

Also Read: Chromosomal Theory of Inheritance

Characteristics of Autosomes and Allosomes

Autosomes and Allosomes contain DNA, and proteins and segregate during cell division. Both are responsible for inheritance and determining an organism’s characteristics. The characteristics of the Autosomes and Allosomes are:

Autosomes

These chromosomes determine an organism’s somatic or physical characteristics. They are also known as somatic chromosomes. 

• Autosomes are numbered from 1 to 22. 
• They lack genes that determine an individual’s sex. 
• In humans, there are 22 pairs of autosomes, they are structurally similar in both males and females.
• It carry genes that control general traits such as hair color, eye color, and other non-sex-related characteristics.
• Autosomes follow Mendelian inheritance patterns, with one copy inherited from each parent.
• During meiosis, autosomes undergo homologous pairing, where corresponding autosomes from each parent align.

Allosomes

These chromosomes determine an organism’s sex and sex-linked inheritance. They are also known as sex chromosomes.

• Allosomes are labeled with letters XY, XO, ZO, or ZW. 
• Allosomes are the sex chromosomes and constitute the 23^rd pair in humans and these are of two types: X and Y chromosomes.
• Allosomes may exhibit sex-specific inheritance patterns or non-mendelian inheritance.
• It carry genes responsible for sexual characteristics that determines an individual’s sex and control the development of secondary sexual characteristics during puberty.
• Inheritance of allosomes may exhibit sex-specific patterns. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
• The combination of X and Y chromosomes determines the sex of an individual during fertilization.

Also Read: Genetics: Introduction, law of inheritance and Sex Determination

Autosomes and Allosomes Functions

The functions of autosomes and allosomes are:

Autosomes Function

Autosome chromosome have the following features:

• Autosomes are non-sex chromosomes that carry the genetic information of the organism.
• Autosomal genes contribute to the determination of most physical and physiological traits. For example: Eye color, height, and metabolic processes.
• Autosome chromosome are present in homologous pairs. It means an individual inherits one autosome from each parent and contributes to genetic diversity.

Also Read: Sex Linked Inheritance

Allosomes Function

Allosome chromosome have the following features:

• Allosomes also known as sex chromosomes helps in determining the sex of an individual. In mammals, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
• Genes located on the sex chromosomes are called sex-linked genes and these genes can be responsible for traits or conditions that are specific to one sex.
• In XY chromosome, males are hemizygous for genes on the X chromosome. It means they have only one copy of each X-linked gene and this can have implications for genetic disorders carried on the X chromosome.
• The combination of X and Y chromosomes during reproduction contributes to genetic diversity.

Also Read: Sex Determination

How Do Allosomes Work?

Allosomes work in the following way:

• Sex Determination
  • In humans, sex is determined by allosomes. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
  • The presence of the Y chromosome is responsible for the development of male characteristics. The absence of the Y chromosome leads to the development of female characteristics.
• Inheritance of Sex-Linked Traits
  • Allosomes carry genes responsible for sex-linked traits, with many of these genes located on the X chromosome.
  • Females (XX) usually express both X chromosomes, whereas males (XY) express genes from the X chromosome inherited from the mother. The Y chromosome in males carries genes related to male development.
• Hemizygosity in Males
  • Males are hemizygous for X-linked genes, having only one copy of each gene on the X chromosome. This is because they lack a second X chromosome to compensate.
  • X-linked recessive disorders are more frequently expressed in males, as there is no second X chromosome to mask the effects of the recessive allele.
• Genetic Diversity
  • The combination of X and Y chromosomes during fertilization contributes to genetic diversity in offspring.
  • The sex of the offspring is determined by whether a sperm carrying an X or a Y chromosome fertilizes the egg.
• Variations in Sex Determination Systems
  • Different species may have variations in their sex determination systems. For example, birds and reptiles often use the ZW system, where females are ZW, and males are ZZ.
  • The mechanisms of allosomes can vary across species, impacting sex determination and inheritance patterns.

Also Read: X-Linked Recessive Inheritance

How Do Autosomes Work?

Autosomes are non-sex chromosomes that carry the genetic information of an organism.

• General Genetic Information:
  • Autosomes carry genes that determine a wide range of physical and physiological traits, excluding those associated with sex determination.
• Homologous Pairs:
  • Autosomes exist in homologous pairs, with one chromosome inherited from each parent.
  • Homologous chromosomes carry similar genes at corresponding loci, contributing to genetic diversity in offspring.
• Determination of Most Traits:
  • Genes located on autosomes determine the majority of an individual’s traits, such as eye color, height, and metabolic processes.
  • Autosomal genes contribute to the inheritance of both dominant and recessive traits.
• Genetic Diversity
  • The combination of alleles from both parents, each contributing an autosome, leads to genetic diversity in the population.
  • During meiosis genetic recombination results in combinations of alleles on autosomes, further enhancing diversity.
• Independent Assortment
  • Autosomes assort independently, during the formation of gametes. This means the inheritance of one autosome does not influence the inheritance of another.
  • Independent assortment contributes to the wide variety of genetic combinations possible in offspring.
• Mendelian Inheritance
  • Autosomal genes follow Mendelian principles of inheritance, where traits are determined by the combination of alleles inherited from both parents.
  • Autosomal inheritance includes patterns such as dominant-recessive relationships and co-dominance.
• Role in Genetic Disorders
  • Many genetic disorders result from mutations or abnormalities in autosomal gene.
  • Autosomal recessive disorders typically require two copies of a mutated gene (one from each parent) for the disorder to manifest.

Also Read: What are Inherited Traits? Definition & Examples

Difference Between Autosome and Allosome

Difference Between Autosome and Allosome are as given below:

Feature	Autosomes	Allosomes (Sex Chromosomes)
Location	Found in both males and females	Found in pairs in females; XY in males
Number	Typically present as pairs (homologous)	One pair of sex chromosomes (XX or XY)
Inheritance	Inherited from both parents	Inherited from both parents
Role in Sex Determination	Not involved in sex determination	Directly involved in sex determination
Genetic Diversity	Contribute to overall genetic diversity	Contribute to genetic diversity and sex determination
Determination of Sex-Linked Traits	Not directly involved in sex-linked traits	Directly involved in sex-linked traits
Hemizygosity (in XY system)	Not applicable	Males are hemizygous for X-linked genes
Expression in Males (in XY system)	Not applicable	Only one X chromosome is active in males
Example in Humans	Chromosomes 1-22	X and Y chromosomes

Genetic Disorders of Autosomes and Allosomes

Genetic disorders can be classified based on whether they affect autosomes or allosomes (sex chromosomes). Various genetic disorders are explained below:

• Cystic Fibrosis (CF): It is an autosomal recessive disorder that affect the CFTR gene on chromosome 7. It affects the respiratory, digestive, and reproductive systems and leads to the production of thick and sticky mucus.
• Sickle Cell Anemia: It is an autosomal recessive disorder that affect HBB gene on chromosome 11. Abnormal hemoglobin leads to abnormal shape red blood cells, causing anemia and other complications.
• Huntington’s Disease: It is an autosomal dominant disorder that affects HTT gene on chromosome 4. Progressive degeneration of nerve cells in the brain, leading to motor dysfunction and cognitive decline.
• Down Syndrome: It is Trisomy 21 (Extra copy of chromosome 21) that results in Intellectual disability, developmental delays, distinctive facial features, and increased risk of certain health issues.
• Hemophilia: It is an X- linked recessive disorder that results in impaired blood clotting and results in excessive bleeding and bruising.
• Color Blindness: It is an X-linked recessive disorder that make it difficult to distinguish between certain colors, particularly red and green.
• Turner Syndrome: It is a chromosomal abnormality of monosomy X (45,X). Girls with a single X chromosome, leading to short stature, infertility, and certain physical features.
• Klinefelter Syndrome: It is chromosomal abnormality of XXY. Boys with an extra X chromosome, leading to tall stature, reduced fertility, and potential learning difficulties.

Conclusion – Autosomes and Allosomes

Autosomes are chromosomes that are not sex chromosomes, while allosomes are sex chromosomes. Humans have 22 pairs of autosomes and one pair of allosomes. Autosomes chromosomes determine somatic traits, while allosomes determine sex. Autosomes have the same form in a diploid cell, while allosomes may differ from one another. Autosomes contain sexual determination genes, even though they are not sex chromosomes.

Also Read:

• Autosomal Recessive Inheritance
• Autosomal Dominant Inheritance
• Difference Between Dominant and Recessive Traits

FAQs on Autosomes and Allosomes

What are the Autosomes?

Autosomes are chromosomes that are not sex chromosomes. They are primarily associated with the cell’s various metabolic functions.

How many Autosomes and Allosomes are Present in Human Being?

Humans have 23 pairs of chromosomes, including 22 pairs of autosomes and one pair of allosomes (sex chromosomes).

Where are Allosomes Present in the Human Body?

Allosomes are genes that help determine sexual preference. They are located in the 23rd pair of chromosomes in the human genome. Allosomes are also known as sex chromosomes.

Where does Autosome Replication Take Place?

Chromosome replication occurs in the S-Phase (Synthesis Phase) of the cell cycle. During this phase, DNA molecules replicate.

Do Females have the Same 46 Autosomes as Males?

Yes, females have the same 22 pairs of autosomes as males. In females, both sex chromosomes are X chromosomes. In males, the sex chromosomes are X and Y.

What are Allosomes also Known as?

Allosomes are also known as sex chromosomes. They are chromosomes that carry genes that determine an individual’s sex.

What are the Two Types of Autosomes?

The two types of autosomes are autosomal dominant and autosomal recessive.

What is the Function of the Allosomes?

To determine the sex of an individual and to carry genes that are responsible for sex-linked traits.

How many Autosomes and Allosomes are Present in Human Beings?

Human beings typically have 22 pairs of autosomes and 1 pair of allosomes, making a total of 46 chromosomes.