U4 AOS2 Topic 1: Introduction to Gene Pool

Gene pool is the collection of all genes and alleles in a specific population. Gene pool can be represented by gene frequency.

Calculation of gene frequency:

Gene frequency is the proportion of a particular allele in a population. It can be calculated by dividing the sum of number of alleles in a population by total number of alleles present in that population. The ability of a population to evolve depends on the size of gene pool. Larger gene pool will have variety of alleles therefore results in genetic diversity leading to evolution. There are various factors which influence gene pool and mutation is one of them.

Mutation:

Changes in DNA result in different types of mutations which introduce new alleles to the population and therefore influence the gene pool.   Certain mutagens can cause permanent changes in DNA known as mutation.  Mutation in a gene can affect the expression of that gene and can be categorized as:

·        Advantageous mutation: A mutation that has positive effect on survivability of an individual by producing a beneficial protein.

·        Deleterious mutation: A mutation that has negative effect on survivability of an individual by producing an abnormal protein.

If there is mutation in a germline cell, then this mutation can be passed to the next generation. Heritable mutation can introduce new alleles into a population and therefore cause genetic diversity.

Types of mutations:

Depending on the change in only one nucleotide or cluster of nucleotides, mutation can be classified as point mutations and block mutations.

1.   Point mutation:

 Point mutation occurs when there is change in one nucleotide only. It can be further classified into following types:

·        Silent mutation: Substitution of a single nucleotide that causes no change of amino acid resulting in no effect on protein formed.

·        Missense mutation: substitution of a single nucleotide that causes an amino acid in a polypeptide chain to change resulting in a faulty protein.

·        Non-sense mutation: substitution of a single nucleotide resulting in formation of stop codon resulting in termination of polypeptide chain.

·        Frameshift mutation: insertion or deletion of a nucleotide resulting in the change in reading frame of nucleotides in mRNA and formation of a different polypeptide chain.

 

2.   Block mutation:

Block mutation, also known as chromosomal mutation results from change in cluster of nucleotides or a part of chromosome. It can be classified into:

·        Deletion: removal of a part of chromosome.

·        Duplication: replication of a part of chromosome.

·        Inversion: a part of chromosome is turned upside down.

·        Translocation: switching of two sections of two different chromosomes.

Block mutation can also result in a change in the number of chromosomes resulting in aneuploidy and polyploidy.

·        Aneuploidy: results from loss or gain of one or more chromosomes.

·        Polyploidy: results from addition of whole set of chromosomes.