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
Q1. Do Autosome Play Role in Sex Determination?
Ans: Not directly, but the chromosome 17 has a gene called SOX9, which activates TDF factor. This factor paly's an important role in determining male sex as this is encoded by SRY gene found on Y chromosome. Mutation of the SOX9 gene also leads to production of female offspring.
Q2. How is Sex Determined by Allosomes?
Ans: All humans have half allosomes( sex determining chromosome) from each of their parents. Females with XX chromosomes pass either of X, while males with XY chromosome can pass either X or Y. An offspring will become female if it receives both X chromosomes from each of the parents. A male child will be born if X chromosome is received from mother and Y chromosome from father.
Q3. Briefly Explain the Functions of Autosomes.
Ans: Autosomes perform a wide range of functions. They have a large number of genes located on each chromosome that perform a particular role and exhibit a particular trait.
Say, for example autosomes are responsible for giving skin color. This task will be accomplished by production of melanin pigment which in turn will be produced in body by translation process. The sequence of amino acids for production of melanin is mapped onto autosomes which transfer this information to m-RNA through the transcription process. Thus autosomes are responsible for a wide array of functions in the human body.
Q4. Give Examples of Autosomal Disorders
Ans: Deletion, duplication, translocation etc. at the time of replication may result in improper number of chromosomes in cells and may lead to various disorders. Some autosomal disorders are-
Trisomy(Down's Syndrome)- it occurs when cells carry an extra copy of chromosome 21 from one of the parents. Such a condition happens due to failure of segregation during the meiosis stage. Children born with this syndrome have retarded mental growth, poor skeleton development and high susceptibility towards diseases.
Lejeune's Syndrome- this happens due to inheritance of a part of chromosome 5. People born with such disorders have small head, heart problems etc.
Philadelphia chromosome- it is due to translocation between chromosome 9 and chromosome 22. Because of it cell replication is uncontrolled as in case of leukemia.
