Question

1. a. Explain what mutations are, what causes them and whether mutations are beneficial or harmful to organisms and why.

b. Define and distinguish between frameshift, missense, nonsense, and silent mutations.

Answer 1

1.a.The sudden,stable,inheritable change in genetic material of an organisms is termed as mutation.The organisms which undergoes mutation is called mutant.The agent of mutation is called mutagen.The unit of mutation is called muton.

Causes:- i.During replication DNA fails to copy its own bases.this slight differences from the original DNA brings out mutations .

ii.when DNA come in contact with chemicals or radiation like UV ,breakdown of DNA occurs.Mutated DNA results because UV light causes thymine dimer to break.

Beneficial effects of mutations:-

a.Mutations brings out evolution.mutation gives a new versions of protein and help the the organisms to cope with external environment.

b.Mutations also gives antibiotic resistant  strains of bacteria which can survive in antibiotics.

Harmful effects of Mutations:-

Many diseases are caused by mutation in genes like cystic fibrosis or cancer.In haemophilia it is sex linked recessive disorder.patient continues to bleed even on a minor cut because of a defect in blood coagulation.The gene for haemophilia is located on X chromosomes.

b.Silent mutations:- Any gene mutations which does not result in phenotypic expression is called silent mutations.

Missense mutations:-mis-sense mutations at the termination codon(in which non -sense codon is converted in to sense codon) results in to an infinitely long polypeptide chain.such chains are also biologically inactive most of the times.

Non-sense mutations:-A non sense mutation at 3' end of DNA template does not affect the polypeptide chain ,except this chains will be smaller than normal chain.

Frameshift mutations:-frame shift mutations deriverd from the fact that there is shift in reading frame either backward or forward.it occurs by 3 ways deletion,insertion or simultaneous deletion and insertion.