Question:

Arrangement of sex chromosomes in Klinefelter's syndrome is

Updated On: Aug 2, 2023

$XX$
$XY$
$XXY$
$XO$

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The Correct Option is C

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Klinefelter's syndrome is formed by the union of an $XX$ egg and a normal $Y$ sperm or normal $X$ egg and abnormal $XY$ sperm. The individual has $47$ chromosomes $(44 + XXY)$. Such persons are sterile males with undeveloped testes, mental retardation, sparse body hair, and long limbs and with some female characteristics such as enlarged breasts. It is considered that the more the $X$ chromosomes, the greater is the mental defect. As the syndrome has two $X$ chromosomes, one barr body is seen in this case.

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Ans: The chromosomal arrangement in Klinefelter’s syndrome is XXY. It has an extra X chromosome. It occurs in males. Normally in males the chromosome XY is present, but due to an addition of another X chromosome it has a total of 47 chromosomes. It is written as 47, XXY. This occurs during the formation of eggs or sperm. It is a genetic disorder. It will affect the sexual development and reproductive function of males. Some of the characteristics features are: reduction in the testosterone production, tall stature, infertility etc. Some individuals may have mild symptoms and go undiagnosed, while others may have more noticeable features and seek medical attention.

It is not an inherited syndrome, it is due to the random non disjunction during gametes formation. The treatment aims at the specific symptoms and can be done by testosterone replacement therapy. The quality of life can be improved after care and awareness.

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Notes on Principles of Inheritance and Variation

Concepts Used:

Principles of Inheritance and Variation - Mutation

A Mutation is a change in the sequence of our DNA base pairs caused by numerous environmental stimuli such as UV light or mistakes during DNA replication. Germline mutations take place in the eggs and sperm and can be passed onto offspring, whereas somatic mutations take place in body cells and are not passed on.

Types of Mutations

There are three types of mutations, which are as follows:

Silent mutation

It refers to any change in DNA sequence that has no effect on the amino acid sequence in a protein or the functions that a protein performs. There is no phenotypic indication that a mutation has occurred.

Nonsense mutation

When there is a change in the sequence of base pairs due to a point mutation, that results in a stop codon. This leads to a protein that is either shortened or non-functional.

Missense mutation

A missense mutation occurs when a point mutation causes a change in the codon, which then codes for another amino acid.

The mutation is caused by the following factors:

Internal Causes

When DNA copies incorrectly, the majority of mutations occur. Evolution occurs as a result of all of these mutations. DNA makes a copy of itself during cell division. When a copy of DNA isn't flawless, it's called a mutation since it differs somewhat from the original DNA.

External Causes

When certain chemicals or radiations are used to break down DNA, it causes the DNA to break down. The thymine dimers are broken by UV radiation, resulting in altered DNA.