Question:

A 10 years old patient is found to have the following clinical features: slanting eyes with epicanthic fold of the eyelid, hypertelorism, dysplastic ears, mongoloid face and protruding tongue. The above mentioned features are associated with which syndrome?

Updated On: Jun 21, 2022
  • Down's syndrome
  • Klinefelter's syndrome
  • Turner's syndrome
  • Cri-du chat syndrome
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The Correct Option is A

Solution and Explanation

Down's syndrome is the trisomy of 21 st chromosome (autosomal aneuploidy) in man. Down's syndrome is characterized by short stature, warty skin, protruding tongue, slanting eyes, with folded eyelids (epicanthus folds), short, broad hands with palmer crease, fingers showing characteristic fingerprint patterns. The affected person's face presents a typical mongoloid look. Hence it is also called as mongoloid idiocy. It occurs due to the phenomenon of non-disjunction. Noh-disjunction occurs when a pair of homologous chromosomes does not separate in meiosis but migrate to the same pole of the cell resulting in an uneven number of chromosomes in the daughter cells (47 in one and 45 in other). This numerical abnormality results in trisomy, (2n + 1) and monosomy (2n- 1) respectively. Non-disjunction is more common in sex chromosomes.
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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.