Autosomes and Allosomes - Overview & Differences

Autosomes and Allosomes - Overview & Differences

Edited By Irshad Anwar | Updated on Jul 02, 2025 05:27 PM IST

Autosomes and allosomes are important genetic terms which define the variation that exists in the number of chromosomes carrying genetic traits and constitute an individual's genetic makeup. These terms are discussed in the chapter Principles of Inheritance and Variation, class 12. This article includes the difference between autosomes and allosomes, their functions, and their role in inheritance. Understanding autosomes and allosomes helps form the core base of genetics which is important for competitive exams like NEET where Biology is one of the major subjects asked.

This Story also Contains
  1. What are Autosomes?
  2. What are Allosomes?
  3. Difference Between Autosomes and Allosomes
  4. Similarities between Autosomes and Allosomes
  5. Importance of Autosomes and Allosomes in Biology
  6. Autosomes and Allosomes in Genetics
  7. Facts about Autosomes and Allosomes
  8. Types of Questions and Weightage for Autosomes and Allosomes

What are Autosomes?

Autosomes are chromosomes that do not determine sex. In the human body, they exist in 22 pairs, carrying most of the genetic information on traits such as eye colour, blood type, and metabolism. They are the same in males and females and are determined by size and structure. General body functions and development mainly depend on autosomes. Changes in autosomes may cause several genetic disorders.

What are Allosomes?

Allosomes or sex chromosomes are the chromosomes responsible for the determination of sex in an organism. Human beings have one pair of allosomes bearing two X chromosomes in females and one X and one Y chromosome in males. Such chromosomes carry genes not only for sexual characters but also for other sex-linked traits like colour blindness and haemophilia.

Difference Between Autosomes and Allosomes

Autosomes and allosomes are one of important topics among the differences and comparison articles in Biology. The table below describes the major differences between autosomes and allosomes:

ParameterAutosomesAllosomes
Number22 pairs in humans.1 pair in humans.
Role in Sex DeterminationNot involved in sex determination.Determines sex (XX in females, XY in males).
PresenceSame in both sexes.Differs between sexes.
Genetic RoleCarries genes for general traits and metabolism.Carries genes for sex-linked traits.
Inheritance PatternOne from each parent, equally inherited.Males inherit X or Y from their father, and X from their mother.
Variation Among SpeciesThe number remains similar in most species.Varies widely among species.
Mutation EffectsMutations can lead to metabolic or structural disorders.Mutations often lead to sex-linked disorders (e.g., colour blindness).
Chromosome SizeGenerally larger and more stable.Y chromosome is smaller and more prone to mutations.
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Similarities between Autosomes and Allosomes

  • Autosomes and allosomes are components of chromosomes.

  • They can be located in the genome of an organism.

  • In both, DNA and proteins are present.

  • They include details about a person's forebears.

  • They both possess genes.

  • They are found in pairs.

  • Anomalies in both types of chromosomes can lead to many genetic diseases.

Importance of Autosomes and Allosomes in Biology

The concept of autosome and allosome is important for students studying biology at class 12 and NEET levels in understanding the concepts of inheritance, genetic variation, and disorders. Thus, autosomal and allosomal knowledge form the basis of advanced topics that include chromosomal abnormalities, sex-linked inheritance, and genetic counselling.

Autosomes and Allosomes in Genetics

Autosomes and allosomes complement each other in genetics. While autosomes are involved in determining the general phenotype as they carry genes responsible for most traits, allosomes are significant in determining sex and hence associate characters. In this sense, it is also crucial in explaining why some genetic disorders like Turner syndrome or Klinefelter affect the allosomes and hence influence sex characteristics.

Facts about Autosomes and Allosomes

  • Autosomes are chromosomes that are devoid of any sex-specific genes.

  • Due to the homomorphism of autosomes, the centromere is located in the same place.

  • On autosomes, there are 200–2000 different genes. In humans, chromosome 1 is the biggest chromosome and contains over 2800 genes.

  • The majority of chromosomes in a genotype are autosomes.

  • On the chromosomes of both men and women exist sex-determining genes (but may also carry many other genes that have nothing to do with sex).

  • Due to heteromorphic sex chromosomes, the position of the centromere varies between male and female chromosomes. Both male and female chromosomes have the same location for the centromere.

Types of Questions and Weightage for Autosomes and Allosomes

The table below indicates the weightage and types of questions asked from autosomes and allosomes in different exams:

Exam TypeTypes of QuestionsWeightage
CBSE ExamsShort answer questions on the differences between autosomes and allosomes, with examples3-5%
NEETMultiple-choice questions (MCQs) on the structure and roles of autosomes and allosomes2-3%
AIIMSAssertion and reasoning questions on inheritance patterns and functions of autosomes and allosomes2-3%
Nursing ExamsTrue/False questions on the number, role, and impact of autosomes and allosomes1-3%

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Frequently Asked Questions (FAQs)

1. How do autosomal chromosomes function?

Autosomal chromosomes function by carrying genes that encode for a wide range of traits and metabolic processes essential for an organism's development and maintenance. They are involved in various cellular functions, including growth, immune response, and metabolic activities. Autosomal chromosomes operate through the expression of these genes, influencing physical traits and physiological functions without determining the sex of the individual.

2. Do Women possess 46 autosomes?

Yes, women possess 46 chromosomes in total, which include 22 pairs of autosomes and one pair of sex chromosomes (XX). Therefore, women have 44 autosomes (22 pairs) and 2 sex chromosomes, making up the complete set of 46 chromosomes.

3. Does the XXY chromosome exist?

Yes, the XXY chromosome configuration does exist. This chromosomal pattern is known as Klinefelter syndrome, a genetic condition that affects males. Individuals with Klinefelter syndrome typically have one extra X chromosome, resulting in a total of 47 chromosomes (44 autosomes and 3 sex chromosomes: XXY). This condition can lead to various physical and developmental traits, including reduced testosterone levels, gynecomastia and fertility issues.

4. What are allosomes?

Allosomes are sex chromosomes that are different in shape, size, or behaviour from a typical autosome. A typical pair of allosomes is the human sex chromosomes. In contrast to sperm, which can include either X or Y chromosomes, the X chromosome is present in the ovum.

5. Are Autosomes haploid or diploid?

Haploid and diploid cells both include autosomes. Chromosomes called autosomes don't affect sex determination. Human body cells are diploid, which means they contain two sets of autosomes—one from the mother and one from the father.

6. How do autosomes and allosomes differ in their gene content?
Autosomes contain genes for various traits and functions throughout the body. Allosomes, particularly the Y chromosome, have fewer genes. The X chromosome contains many genes unrelated to sex determination, while the Y chromosome primarily carries genes involved in male development.
7. How do autosomes differ from allosomes in terms of inheritance patterns?
Autosomes are inherited equally from both parents, while allosomes have different inheritance patterns. In humans, females inherit one X chromosome from each parent, while males inherit an X from their mother and a Y from their father.
8. How do autosomes and allosomes behave differently during meiosis?
During meiosis, autosomes pair up and undergo crossing over, exchanging genetic material. Allosomes behave differently: in males, the X and Y chromosomes pair only at small homologous regions, limiting crossing over between them.
9. What is X-inactivation, and why doesn't it occur in autosomes?
X-inactivation is a process in female mammals where one X chromosome is randomly inactivated in each cell to equalize gene expression between males and females. This doesn't occur in autosomes because they are present in equal numbers in both sexes.
10. How do mutations in autosomes and allosomes differ in their inheritance patterns?
Mutations in autosomes can be inherited from either parent and affect both males and females equally. Mutations in allosomes, particularly X-linked mutations, often show different inheritance patterns between males and females due to the presence of only one X chromosome in males.
11. How do autosomes and allosomes differ in their susceptibility to certain types of mutations?
Allosomes, particularly the X chromosome in males, are more susceptible to the effects of recessive mutations because there's no second copy to mask the effects. Autosomes are generally more resistant to recessive mutations as both copies need to be affected for the trait to be expressed.
12. How do autosomes and allosomes differ in their methylation patterns?
Allosomes, particularly the inactive X chromosome in females, show higher levels of DNA methylation compared to autosomes. This difference in methylation patterns is crucial for X-inactivation and dosage compensation.
13. How do autosomes and allosomes differ in their gene density?
Autosomes generally have a higher gene density compared to allosomes. The X chromosome has a moderate gene density, while the Y chromosome has the lowest gene density, containing mostly genes related to male development and fertility.
14. What is dosage compensation, and why is it necessary for allosomes but not autosomes?
Dosage compensation is a mechanism to equalize gene expression between males (XY) and females (XX). It's necessary for allosomes because females have two X chromosomes while males have only one. Autosomes don't require dosage compensation as they are present in equal numbers in both sexes.
15. What is the concept of haploinsufficiency, and how does it differ between autosomes and allosomes?
Haploinsufficiency occurs when a single functional copy of a gene is not enough to maintain normal function. It can occur in both autosomes and allosomes but is more common in X-linked genes in males due to the presence of only one X chromosome.
16. What is the relationship between autosomes, allosomes, and sex determination?
While autosomes carry genes that influence various traits, allosomes are primarily responsible for sex determination. In humans, the presence of a Y chromosome typically leads to male development, while its absence results in female development.
17. How do autosomes and allosomes contribute to genetic disorders differently?
Autosomal disorders can affect both sexes equally and are often recessive, requiring two copies of the mutated gene. Allosomal disorders, particularly X-linked disorders, often affect males more frequently or severely due to the presence of only one X chromosome.
18. What is the significance of the SRY gene on the Y chromosome?
The SRY (Sex-determining Region Y) gene on the Y chromosome is crucial for male sex determination. It initiates a cascade of events leading to the development of male characteristics, highlighting the importance of allosomes in sex determination.
19. How do autosomes and allosomes differ in their evolutionary rates?
Allosomes, particularly the Y chromosome, tend to evolve faster than autosomes. This is partly due to the Y chromosome's limited recombination and exposure to more mutations in the male germline.
20. What is genomic imprinting, and how does it relate to autosomes and allosomes?
Genomic imprinting is an epigenetic phenomenon where certain genes are expressed differently depending on which parent they were inherited from. It occurs on both autosomes and the X chromosome but not on the Y chromosome.
21. What are autosomes and allosomes?
Autosomes are chromosomes that are not sex chromosomes and are present in both males and females. Allosomes, also known as sex chromosomes, determine the sex of an organism. In humans, there are 22 pairs of autosomes and 1 pair of allosomes.
22. How many autosomes do humans have?
Humans have 22 pairs of autosomes, for a total of 44 autosomes. These are numbered from 1 to 22 based on their size, with chromosome 1 being the largest and chromosome 22 being the smallest.
23. How do autosomes and allosomes contribute to genetic diversity?
Both autosomes and allosomes contribute to genetic diversity through independent assortment during meiosis and crossing over. However, allosomes also contribute to diversity through sex determination and sex-linked traits.
24. What is aneuploidy, and how does it affect autosomes and allosomes differently?
Aneuploidy is an abnormal number of chromosomes. Autosomal aneuploidy (e.g., trisomy 21 in Down syndrome) often has more severe effects than allosomal aneuploidy (e.g., XXY in Klinefelter syndrome) because autosomes contain more essential genes.
25. What is the difference between homologous and non-homologous chromosomes?
Homologous chromosomes are pairs of chromosomes that carry the same genes but may have different alleles. Non-homologous chromosomes carry different genes. Autosomes are always homologous pairs, while allosomes can be homologous (XX in females) or non-homologous (XY in males).
26. What is the significance of pseudoautosomal regions on sex chromosomes?
Pseudoautosomal regions are homologous sequences on the X and Y chromosomes that allow for pairing and recombination during meiosis in males. These regions behave more like autosomes and ensure proper segregation of sex chromosomes during cell division.
27. How do autosomes and allosomes contribute to the concept of genetic load in a population?
Both autosomes and allosomes contribute to genetic load, which is the reduction in population fitness due to deleterious mutations. However, allosomes, particularly the X chromosome in males, may contribute disproportionately due to the expression of recessive deleterious alleles.
28. How do autosomes and allosomes differ in their roles in cancer development?
Both autosomes and allosomes can harbor genes involved in cancer development. However, some cancers show sex-specific incidence rates, suggesting a role for allosomes. Additionally, X chromosome inactivation can influence cancer risk in females.
29. What is the concept of sex-reversal syndromes, and how do they relate to autosomes and allosomes?
Sex-reversal syndromes occur when an individual's chromosomal sex (XX or XY) doesn't match their phenotypic sex. These syndromes can result from mutations in genes on either autosomes or allosomes that are involved in sex determination and development.
30. What is the concept of mosaicism, and how does it manifest differently in autosomes and allosomes?
Mosaicism occurs when an individual has two or more genetically distinct cell populations. It can occur in both autosomes and allosomes but may manifest differently. For example, X chromosome mosaicism in females can lead to variable expression of X-linked traits.
31. What is the significance of X-linked dominant inheritance, and how does it differ from autosomal dominant inheritance?
X-linked dominant inheritance occurs when a dominant allele is on the X chromosome. It differs from autosomal dominant inheritance in that males are more severely affected (as they have only one X chromosome), and father-to-son transmission doesn't occur.
32. What is a karyotype, and how does it help in identifying autosomes and allosomes?
A karyotype is a visual representation of an organism's chromosomes, arranged by size and shape. It helps identify autosomes and allosomes by showing the number and appearance of chromosomes. In humans, the 22 pairs of autosomes are easily distinguishable from the X and Y allosomes.
33. How do autosomes and allosomes contribute to sexual dimorphism?
While allosomes play a primary role in sex determination, both autosomes and allosomes contribute to sexual dimorphism. Allosomes carry sex-specific genes, while autosomes contain genes that respond to sex hormones, influencing secondary sexual characteristics.
34. What is the concept of sex-limited genes, and how do they relate to autosomes and allosomes?
Sex-limited genes are those expressed in only one sex, despite being present in both. These genes can be located on either autosomes or allosomes but are activated or repressed based on the hormonal environment, contributing to sex-specific traits.
35. How do autosomes and allosomes contribute to genetic drift differently?
Genetic drift affects both autosomes and allosomes, but its effects can be more pronounced on allosomes, particularly the Y chromosome. This is due to the smaller effective population size of allosomes, especially in species with skewed sex ratios.
36. How do autosomes and allosomes differ in their recombination rates?
Autosomes generally have higher recombination rates than allosomes. The X chromosome has a lower recombination rate than autosomes, while the Y chromosome has very limited recombination, occurring only in small pseudoautosomal regions.
37. What is the role of autosomes and allosomes in genetic counseling and prenatal testing?
Both autosomes and allosomes are important in genetic counseling and prenatal testing. Autosomal disorders are often screened for (e.g., Down syndrome), while allosomal analysis can reveal sex chromosome abnormalities and sex-linked disorders.
38. How do autosomes and allosomes contribute to species evolution and speciation?
Both autosomes and allosomes contribute to evolution and speciation through mutations and genetic drift. However, allosomes, particularly the rapidly evolving Y chromosome, may play a more significant role in reproductive isolation and speciation events.
39. How do autosomes and allosomes contribute to genetic diversity in populations?
Autosomes contribute to genetic diversity through independent assortment and crossing over during meiosis. Allosomes add to this diversity through sex-specific inheritance patterns and the unique evolution of the Y chromosome.
40. What is the concept of sex-influenced traits, and how do they relate to autosomes and allosomes?
Sex-influenced traits are controlled by autosomal genes but are expressed differently in males and females due to hormonal influences. These traits highlight the complex interplay between autosomes and the sex-determining effects of allosomes.
41. What is the concept of X-linked recessive inheritance, and how does it differ from autosomal recessive inheritance?
X-linked recessive inheritance occurs when a recessive allele is on the X chromosome. It differs from autosomal recessive inheritance in that males are more likely to express the trait (as they have only one X chromosome), and the inheritance pattern shows a characteristic "criss-cross" pattern.
42. What is the significance of Y chromosome microdeletions in male infertility?
Y chromosome microdeletions are a significant cause of male infertility, highlighting the importance of allosomes in reproductive health. These deletions affect genes crucial for sperm production and function, a role not typically associated with autosomes.
43. What is the significance of X chromosome inactivation in dosage compensation, and why isn't it necessary for autosomes?
X chromosome inactivation equalizes gene expression between XX females and XY males. It's not necessary for autosomes because they are present in equal numbers in both sexes, maintaining a balanced gene dosage without additional compensation mechanisms.
44. What is the significance of X-linked dominant lethal mutations, and how do they differ from autosomal dominant lethal mutations?
X-linked dominant lethal mutations are fatal when present in males (who have only one X chromosome) and in homozygous females. They differ from autosomal dominant lethal mutations in their inheritance pattern and sex-specific effects.
45. What is the significance of X chromosome skewing in females, and how does it relate to autosomal gene expression?
X chromosome skewing refers to the non-random inactivation of one X chromosome in females. This can lead to variable expression of X-linked genes and can interact with autosomal gene expression, potentially influencing disease susceptibility and phenotypic variation.
46. Why are autosomes called "body chromosomes"?
Autosomes are called "body chromosomes" because they contain genes that determine various physical and physiological traits of an organism, such as eye color, height, and blood type. These traits are not directly related to sex determination.
47. How do autosomes and allosomes contribute to the concept of genetic architecture in complex traits?
Both autosomes and allosomes contribute to the genetic architecture of complex traits. Autosomes typically harbor the majority of genes influencing these traits, while allosomes can contribute sex-specific effects and unique inheritance patterns, adding complexity to trait expression and heritability.
48. What is the concept of sex-specific selection, and how does it affect the evolution of autosomes and allosomes differently?
Sex-specific selection occurs when natural selection acts differently on males and females. It can affect both autosomes and allosomes but often has a more pronounced effect on allosomes, particularly in shaping sex-specific traits and behaviors.
49. How do autosomes and allosomes differ in their rates of mutation accumulation?
Allosomes, particularly the Y chromosome, tend to accumulate mutations faster than autosomes. This is partly due to the Y chromosome's limited recombination and its exclusive presence in males, where it undergoes more cell divisions during spermatogenesis.
50. How do autosomes and allosomes differ in their roles in embryonic development?
While autosomes play crucial roles throughout embryonic development, allosomes are particularly important in early sex determination. The presence or absence of the Y chromosome triggers cascades of gene expression that guide male or female development.
51. How do autosomes and allosomes contribute to the phenomenon of hybrid incompatibility in speciation?
Both autosomes and allosomes can contribute to hybrid incompatibility, but allosomes often play a more significant role. The "faster-X" hypothesis suggests that X-linked genes evolve more rapidly, potentially leading to reproductive isolation between populations.
52. What is the concept of parental imprinting, and how does it relate to autosomes and allosomes?
Parental imprinting is an epigenetic phenomenon where certain genes are expressed differently depending on which parent they were inherited from. It occurs on both autosomes and the X chromosome but not on the Y chromosome, affecting inheritance patterns of certain traits.
53. How do autosomes and allosomes contribute to the phenomenon of heterosis or hybrid vigor?
Both autosomes and allosomes contribute to heterosis, but their contributions may differ. Autosomal genes play a major role in many hybrid vigor traits, while allosomal genes, particularly on the X chromosome, may contribute to sex-specific aspects of hybrid vigor.
54. How do autosomes and allosomes differ in their roles in epigenetic inheritance?
Both autosomes and allosomes are subject to epigenetic modifications, but allosomes show unique patterns. The X chromosome undergoes extensive epigenetic regulation during X-inactivation, while the Y chromosome has evolved specific epigenetic mechanisms to maintain its integrity.
55. How do autosomes and allosomes contribute to the phenomenon of sexual antagonism in evolution?
Sexual antagonism occurs when a trait is beneficial to one sex but detrimental to the other. Both autosomes and allosomes can harbor sexually antagonistic genes, but allosomes, particularly the X chromosome, may accumulate these genes more readily due to their sex-specific inheritance patterns.

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