CHAPTER 5 :- ORIGIN AND EVOLUTION OF LIFE

Q.: Write a note on genetic drift?

Ans.: 1) The term refer to the elimination of certain fruits when a section of       population migrates or dies due to natural calamity.

2) It is also known as Sewall Right effect as it was explained by Sewall right.

3) It alters the gene frequency of remaining population which causes    variation.

4) All populations show genetic drift but its marked effect is seen in small sized population.

5) The genetic drift is explained two effects

a) Founder effects: Formation of different genotype in a new settlement is called as founder effect. (New species may develop).

b) Bottleneck effect: Reduction in the allele frequency is called as bottle check effect which often prevents species from extinction.

6)  Significance:

1) It is an evolutionary force.

2) It helps the populations to become different because of the probability that each population fixes different population by chance.

Q.: Name the mechanism by which new alleles appear in a population.

Ans.: Mutation is the mechanism by which new alleles appear in a population.

Q.:  Explain various factors that can alter gene frequency.

Ans.: The theory is based on three main concepts which can be explained as follows:-

Genetic variations: 1) the group of interbreeding organism in a specific geographical area is known as population and considered as unit of evolution.

2) Genetic variations actually act as raw material in the process of evolution.

3) The different reasons for genetic variations can explained as follows:-

I) Gene mutation or point mutation: 1) Changes in the chemical makeup of a gene is known as gene mutation or point mutation.

2)  Point mutation bring about variation in gene pool and change the gene frequency.

II) Gene Flow: 1) Transfer of genes between two genetically different populations from one another is called as gene flow.

2) Migration of animals to different regions transfer genes to the gene pool of new area altering the gene frequency.

III) Genetic recombination:

1) It is the result of exchange of genetic material between two homologous chromosomes by the process of crossing over.

In sexual reproduction, gametogenesis brings about new genetic recombination.

2) These genetic recombination are responsible for variations.

VI) Genetic drift / Sewall Right effect: 

1) Any alteration in frequency of an allele in the natural population by pure chance is genetic drift.

2) Sewall Right proposed this concept of genetic drift.

3) Due to genetic drift addition of elimination of specific can occur in a population.

4) Smaller populations have greater chances of genetic drift. These small population under favourable conditions can give barge number of variations.

V) Chromosomal aberrations:

1)  It refers to structural alteration in chromosomes changing the arrangement of genes.

2) The different process like deletion, duplication translocation and inversion can bring about changes in Mendelian population also.

Q.: Explain the role of gene flow in evolution?

Ans.: 1) Gene Flow is also known as gene migration and defined as the movement of individuals from one place to another.

2) It the migrating animals breed with the new population the immigrated animals will add new gene to local gene pool of the hosts. This is gene migration.

3) Many times two isolated populations of the same species come close due to migration.

4) The genes of two district populations intermix through breeding and produce variation in off springs.

Thus gene flow brings about genetic variability in the off spring and helps in evolution.