A person may be a haemophilic, only if his mother is a carrier or colourblind.
The male parent cannot pass on a sex-linked gene to his son.
- If both assertion and reason are true and reason is the correct explanation of assertion
- If both assertion and reason are true but reason is not the correct explanation of assertion
- If assertion is true but reason is false
- If both assertion and reason are false
The Correct Option is A
Approach Solution - 1
The correct option is (A): If both assertion and reason are true and reason is the correct explanation of assertion.
Approach Solution -2
Explanation: Hemophilia is a sex-linked recessive disorder in which the blood does not properly clot.
- The gene responsible for causing hemophilia resides on the X chromosome.
- It is generally passed down from parent to child.
- Females have two X chromosomes and males have one X and one Y chromosome.
- The assertion is true because if a woman is a carrier for the hemophilia gene (meaning she carries one normal X chromosome and one X chromosome with the hemophilia gene), her sons have a 50% chance of inheriting the X chromosome with the hemophilia gene.
- If a son inherits the X chromosome with the hemophilia gene from his carrier mother, he will be hemophilic.
- The reason is true because if the father is hemophilic and the mother is not a carrier or colorblind, there is a 100% chance that the son will not inherit the hemophilia gene from his father (as the son inherits the Y chromosome from his father).
Therefore, option (A) is correct
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Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
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Reason (R) : Liberation of oxygen is due to photolysis of water.
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Reason (R) : Cro-Magnon man had slightly prognathous face.
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- Transcription
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.