Difference between autosomes and allosomes with structure and function
Introduction
Human beings have 46 numbers of chromosomes arranged in a human cell in 23 pairs. These carry information that is passed from the parent to the children through heredity. While the somatic cells contain 46 chromosomes in a diploid form the the sex cells contain only 23 chromosomes in haploid form. But have you ever wondered why there is a discrepancy in the chromosome number of different cells? And which chromosome decides the gender of the offspring?
Autosomes
Out of the 23 chromosomes pairs, 22 pairs are referred to as autosomes.
There are two copies of songs in both females and males. These chromosome are involved in all the functions except for sex determination. They regulate the somatic characters of the body.
These chromosomes regulate all inheritance of organisms characteristics and are responsible for transferring the genetic information from parent to offspring. Several genes in each chromosome perform a specific function.
They are numbered according to their shape and size which means that chromosome 1 with the smallest number, is the largest chromosome in size having 3000 genes on it. Thus, ranging from chromosome 1 to 22 the size of the chromosomes decrease. Except that the chromosome 21 is the smallest chromosome instead of chromosome 22.
Allosomes
23rd pair of chromosome in human beings is referred to as the sex chromosome or allosome.
In females the XX pair of chromosomes is found in males XY pair of chromosomes is found.
These chromosomss help in determining sex of offspring and also transfer sex linked traits from parents to offsprings.
Each chromosome generally has two arms named as 'p' and 'q'. In the case of an XY pair of chromosomes the X chromosome has an equal or similar p and q arm but the Y chromosome has an unequal, one long and one short arm.
Difference Between Autosomes and Allosomes
Autosomes
Somatic chromosomes.
22 pairs
Have more genes
Number of gene varies from 200 - 2000
Homologous pairs of chromosome
Control many traits
Follow Mendelian principles of inheritance
Centromeric position is identical
Allosomes
Sex chromosome
Only 1 pair represented as XO,XY,ZW or ZO
Have less number of genes
Number of gene upto 300
Non homologous pairs
Control only sex determining and sex linked traits
Do not follow Mendelian principles of inheritance
Centromeric position is non identical
Examples of Autosomal Disorders
Autosomal disorders can be identified by amniocentesis. These include-
Klinefelter's syndrome- Identified by Dr. Harry F. Klinefelter. It happens due to an additional copy of X chromosome making the overall chromosome 47 in number in individuals. Symptoms include development of mammary gland, tall stature, rudimentary testis.
Turner's syndrome- This is caused by deletion of X chromosome resulting in 45 chromosomes in individuals. Symptoms include short statured females with rudimentary ovaries.
Triple X syndrome- This is caused by the presence of 3 copies of X chromosome resulting in karyotype 47.
Supermale - In this case 2 copies of Y chromosome are present due to nondisjunction of chromosome at meiosis.
Do You Know?
Why Do Somatic Cells Have Chromosomes Double in Number?
Ans: Eukaryotic organisms have double or two copies of each chromosome which is inherited from each one of the parents. This creates diversity among the offspring and enhances adaptability to the environment. In the case of humans adaptability is in terms of good immune sy, ability to fight against diseases etc. Presence of two copies also enables the chance of passing a healthy copy to the next generation in case one gets mutated.
FAQs on Autosomes and Allosomes in Human Genetics
1. What are autosomes and allosomes?
Autosomes are non-sex chromosomes that determine most body traits, while allosomes are sex chromosomes that determine the biological sex of an organism. In humans:
- There are 22 pairs of autosomes controlling traits like height, eye color, and metabolism.
- There is 1 pair of allosomes (XX in females and XY in males).
- Autosomes are the same in both sexes, but allosomes differ between males and females.
2. What is the difference between autosomes and allosomes?
The main difference between autosomes and allosomes is that autosomes control general body characteristics, while allosomes determine sex and sex-linked traits.
- Autosomes: 22 pairs in humans; same in males and females.
- Allosomes: 1 pair (XX or XY); differ between sexes.
- Autosomes carry genes for most inherited traits, whereas allosomes carry genes for sex determination and sex-linked disorders.
3. How many autosomes and allosomes are present in humans?
Humans have 44 autosomes (22 pairs) and 2 allosomes (1 pair), making a total of 46 chromosomes. Specifically:
- 22 pairs of autosomes are numbered 1 to 22.
- 1 pair of allosomes is either XX (female) or XY (male).
- These chromosomes are found in the diploid cells of the body.
4. What is the function of autosomes?
Autosomes function to carry genes that control most of the body's structural and physiological traits. They:
- Determine characteristics such as height, skin color, and blood type.
- Carry genes involved in metabolism, growth, and development.
- Participate in inheritance patterns like autosomal dominant and autosomal recessive traits.
5. What is the function of allosomes?
Allosomes function to determine the biological sex and regulate sex-linked characteristics in an organism. In humans:
- The X chromosome carries many genes related to general and reproductive functions.
- The Y chromosome contains the SRY gene, which triggers male development.
- They influence inheritance of sex-linked traits like hemophilia and color blindness.
6. What are sex-linked traits?
Sex-linked traits are characteristics controlled by genes located on the sex chromosomes, usually the X chromosome. Key points include:
- Most sex-linked traits are X-linked because the X chromosome carries more genes than the Y chromosome.
- Males (XY) are more likely to express X-linked recessive disorders.
- Examples include hemophilia and red-green color blindness.
7. Are autosomes the same in males and females?
Yes, autosomes are the same in both males and females in number and structure. In humans:
- Both sexes have 22 identical pairs of autosomes.
- The only chromosomal difference between males and females lies in the allosomes (XX vs XY).
- Autosomal genes are inherited equally from both parents regardless of sex.
8. How do allosomes determine sex in humans?
Allosomes determine sex in humans based on the presence or absence of the Y chromosome. The process works as follows:
- If a sperm carrying an X chromosome fertilizes the egg (X), the child is XX (female).
- If a sperm carrying a Y chromosome fertilizes the egg (X), the child is XY (male).
- The SRY gene on the Y chromosome initiates male sex development.
9. What are examples of autosomal disorders?
Autosomal disorders are genetic diseases caused by mutations in genes located on the autosomes. Examples include:
- Sickle cell anemia – an autosomal recessive disorder affecting hemoglobin.
- Cystic fibrosis – an autosomal recessive disorder affecting mucus production.
- Huntington’s disease – an autosomal dominant neurological disorder.
10. What is the role of autosomes and allosomes in inheritance?
Autosomes and allosomes play distinct roles in inheritance by carrying different categories of genes. Specifically:
- Autosomes transmit most traits through autosomal dominant or recessive inheritance.
- Allosomes transmit sex-linked traits through X-linked or Y-linked inheritance.
- Together, they ensure the transmission of genetic information from parents to offspring.
