Question

1. What is the difference between a transition and a transversion? Which type of base substitution is more common?

2. What is the difference between a missense mutation and a nonsense mutation? Between a silent mutation and a neutral mutation?

Answer 1

1.Transition and Transversion mutation both are come under point mutation.It is the mutation in a single base pair ,which is replaced by another base pair.

Transition mutation:-

i.when one base is replaced by another base of same class(A replaced by T and G replacee by C).

ii.As replacement take between same class,so ring structure of nitrogenous base does not change.

iii.This type of base substitution is more common.

iv.In this type of mutation a particular base can undergo single type of transition.

Transversion:-

i.In this type of point mutation purine is transfered to pyrimidine or vice versa.

ii.since replacement take place between two different class,so there is change in ring structure.

iii.It is comparatively less common.

iv.In this type of mutation,a base can undergo two types of transversion.

Transition is more common than Transversion because As transition occur between two similar class of base ,so it is easy to replace one single structure with another single ring structure than substituting a double ring structure for a single ring(as in transversion).

2.Non sense mutation:-

i.In this type of mutation a sense codon is changed to a chain terminating codon.

ii.As a stop codon is introduces at the site of mutation,so it causes premature chain termination which results in formation of an incomplete protein.

iii.This type of mutation produced mostly non functional protein.

iv.Disease like cystic fibrosis and duchenne muscular dystrophy(DMD) are caused by this type of mutation.
Missense mutation:-

i.It is a single base pair substitution in which alternation of genetic code occurs which form a new aminoacid that is different from the usual aminoacid present before at that position.

ii.As it introduces a distinct codon ,so it forms a distinct aminoacid which in result form a protein which can be conservative or non conservative.

iii.This type of mutation produced either functional or non functional protein.

iv.sickle cell anaemia is caused by this type of mutation.

Between a silent and neutral mutation:-This type of mutation brings about changes in the nucleotide sequence of an aminoacid.As silent mutation occurs at third base of codon as genetic code is degenerate,so it does not alter the aminoacid.As there is no difference seen in the function of protein,so silent mutation often considered as neutral mutation(no change in function).