Question

Assertion - An organism with lethal mutation may not even develop beyond zygote stage.
Reason - All types of gene mutations are lethal.
A) Both assertion and reasons are correct and reason is the correct explanation to the assertion
B) Both assertion and reason are correct but reason is not the correct explanation to the assertion
C) Assertion is correct but reason is incorrect
D) Both assertion and reason are incorrect.

Answer 1

All the genes present in an organism are not useful, but some of them show harmful effects and sometimes may cause the death or lethality. Such factors or genes which cause death or lethality in an organism are called lethal genes or factors.

Complete answer:
The lethal factors are fortunately present in the recessive state and thus cause death only in homozygous condition. In heterozygous condition, they may cause structural changes.
An organism with lethal mutation may not even develop beyond zygote stage because sub-vital mutation reduces the chances of survival, whereas supravital mutation improves the biological fitness under certain conditions. Some mutations are neither harmful nor beneficial to the organisms in which they occur.
Gene mutation is the sudden stable change in the structure of genes due to the change in nucleotide sequence and nucleotide type. The gene mutation including change in single nucleotide is known as point mutations, if mutations take place more than one base pair is called gross mutation.
Types of gene mutations: -
Substitution: - when replacement of one type of nitrogenous base by another.
Inversion: - when DNA by mutagen can change the base sequence of cistron in the reverse order.
Frame-shift mutations: - When framing of base sequence shifts laterally either in the forward direction due to insertion of one or more nucleotides or in the backward direction due to deletion of one or more nucleotides. It is also called gibberish mutations.

So, option C is correct. Assertion is correct but the reason is incorrect.

Note:

Sub-vital mutation that causes the death before the maturity of less than 50% of those of individual carriers.
Sublethal mutation causes the death of 90% individuals.