Question:

Which of the following is correct ?

Updated On: Aug 1, 2022

Henking discovered the small Y-chromosome
Drosophila also shows XX-XY sex determination like human
Birds have ZZ-ZW sex determination, where females are ZZ & males are ZW
Grasshoppers show XX-XY sex determination

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The Correct Option is B

Solution and Explanation

Hermann Henking discovered the X chromosome while studying insects in the early 1890s. The sex chromosomes in birds are opposite of that in humans. Human males are heterogametic (XY), females are homogametic (XX), in birds males are homogametic (ZZ) and females are heterogametic (ZW). The "W" is the sex determining chromosome just as the Y in humans. A bird with a W is always a female. In grasshoppers, there is no Y chromosome, so a grasshopper with one X chromosome (symbolized as XO) is normally a male, while a grasshopper with two X chromosomes (XX) is normally a female.

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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.