SBI3UA- Genetic Variation and the Hardy-Weinberg Principle

how was Darwin’s theory of evolution by natural selection incomplete

no accurate understanding of the mechanism of inheritance (role of genetics)

Population Genetics

Discusses how evolution is a change acros generations in the frquencies of alleles

• essentially the changes in the relative abundance of traits of a population is tied to the relative abundance of the alleles that influence them

Gene

 portion of DNA that codes for a trait

Loci

location of a gene on the DNA molecule

Allele 

Different forms of a gene

• E.g. Bb = 2 alleles for eye colour, brown and blue

Homozygous

two identical alleles for a trait

• E.g. bb = homozygous blue

Heterozygous

 two diff alleles for a trait

• E.g. Bb = heterozygous brown

Genome

the complete set of all alleles possessed by an individual organism

• All members of the same species have the same genome

Genotype

the set of alleles

• Genome of a species will be the same, but their specific genotype (combination of alleles) will be different

Phenotype

observable traits coded by the genotype

• Natural selection works on the phenotype, thereby altering the genotype

Genetic variation

• The quantity of DNA and the number of 

  genes are variable among a species

• Variation within a species is a result of the variety and combination of alleles possessed by individuals

how does sexual reproduction cause genetic diversity

• results in random recombination of different alleles and results in a high degree of genetic diversity within most populations

Gene Pool

• the genetic information of an entire population

Population

• members of the same species living in the same region

Allele frequency

• the proportion of gene copies in a population of a given allele

  • Therefore, evolutionary changes can be measured in part by looking for changes in allele frequencies

Hardy-Weinberg principle

Shows that allele frequencies will not change from generation to generation as long as the following conditions are met:

• The population is very large

• Mating opportunities are equal

• No mutations occur

• No migration occurs

• No natural selection occurs – all individuals have an equal chance of reproductive success

Hardy-Weinberg Equation

• For a gene with only two different alleles (A and a)

p = frequency of allele A

q = frequency of allele a

p²+2pq+q² = 1

p² = frequency of AA genotype; 2pq = frequency of Aa genotype; q² = frequency of aa genotype

what is the genotype frequency values between the offspring gens and the parent gens

the frquency values are the same for both

What happens to allele frequencies from gen to gen if random mating occurs

• allele frequencies are likely to remain constant from generation to generation