Pop gen part 1

Chapter 3Chapter 3

Population GeneticPopulation Genetic

Concept review…Population genetic

Gene pool concept

Hardy-Weinberg

Law

At the end of the lesson, you should be able to :

a)Gene pool concept:- Explain gene pool and allele frequency- Explain population genetics and its relation to

allele frequency- Explain allele frequency and genetic equilibrium

Gene pool conceptGene pool concept

Gene pool conceptGene pool concept• Studies the change of frequencies of alleles within a

population

• Population :- a group of individuals of the same species that live in a habitat & may interbreed to produce fertile offspring

- shares a same gene pool

• Gene pool - total aggregate of genes in a population at any one time

- consists of all alleles at all gene loci in all individuals of the population at a given time

Gene pool conceptGene pool concept• For a diploid species, each locus is represented twice in the genome (homozygous /

heterozygous)

• Eg: - A study was done on 10,000 rats, focusing on the fur colour (determined by dominant allele A & recessive allele a)

- Data: AA individuals = 6,000 Aa individuals = 2,000

aa individuals = 2,000

:. Total number of alleles for fur colour = 2(6000) + 2(2000) + 2(2000) = 20000

Gene pool conceptGene pool concept• Each of the allele types has a relative frequency in the gene pool

• Allele frequency: ratio of any given allele in a population, relative to all the other alleles of that gene at the same locus

• Eg: - Using the previous data, calculate the allele frequencies for A & a in the gene pool

- Total of A alleles = 2(6000) + 1(2000)= 14000

- Total of a alleles = 2(2000) + 1(2000)= 6000

- Frequency for A alleles = 14000 / 20000 = 0.7

- Frequency for a alleles = 6000 / 20000 = 0.3

Gene pool conceptGene pool concept• For a gene locus where only 2 alleles occur in a population, allele

frequencies can be calculated using this equation :

p + q = 1

p = frequency of the dominant allele q = frequency of the recessive allele

• If q = 0.3, p = 1 – 0.3= 0.7

Gene pool conceptGene pool concept• Allele frequencies in a gene pool determine the genetic change for a population

• Naturally, the composition of a gene pool may change over time due to certain factors

• Change in allele frequencies

Change in gene pool

Change in genetic composition of population

Evolution

Gene pool conceptGene pool concept• If no change in allele frequencies from

one generation to the next, the gene pool is considered static

• This shows that the gene pool is in genetic equilibrium

Sekilas pandang…

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Sekilas pandang…

Thank you for your attention