9A Gene Pools

U4 AOS2

Species

A biological species is a grouping of organisms that can interbreed to create viable and fertile offspring.

 

Species are recognized on the basis of their morphology (size, shape, appearance) and genomes.

Populations

A population comprises the total number of one species in a particular location.

 

All members of a population have the potential to interact with each other.

Genes

A gene is a segment of DNA that codes for a protein, which can produce a particular trait.

Example: Beetle colour

Alleles

An allele is an alternative version of that gene.

Example: Red, orange, yellow

Genotype

The genotype is the allele combination present for a gene in an individual.

Example:

• RR (homozygous dominant - 2 x dominant alleles)

• Rr (heterozygous - 1 x dominant and 1 x recessive allele)

• rr (homozygous recessive - 2 x recessive alleles)

Phenotype

The phenotype is the expression of a physical trait/characteristic that can be due to:

• One gene only

• Many genes (e.g. eye colour)

• Genes & environmental factors (e.g. height)

Gene Pool

A gene pool is the complete set of genes and alleles present in a population or species.

Gene Pool Analysis

The frequency of alleles and genotypes can determine the state of the gene pool as either:

• Stable or

• Undergoing change

 

Genetic change is an important factor in species evolution.

Allele Frequency

The frequency of alleles in a population can be found by:

 

1. Counting the number of dominant and recessive alleles

2. Convert these to percentages:

Number of Alleles/Total Number of Alleles x 100

Genotype Frequency

To determine the frequencies of different genotypes in a population, count the number of each genotype in the population:

Number of genotype/population x 100

Changing Allele Frequencies

Populations can be subjected to processes that can change the frequency of alleles present, including:

• Mutations

• Gene Flow

• Natural Selection

• Non-Random Mating

• Genetic Drift

Mutations

 

Permanent changes to a DNA sequence can create new alleles.

Gene Flow

Alleles can flow in an out of populations due to migration or interbreeding between populations.

Natural Selection

Environmental selection pressures may reduce reproductive success of individuals.

Genetic Drift

A random event can alter the gene pool.

Non-Random Mating

Individuals seek out others with particular phenotypes to mate with.