14.2 Hardy-Weinberg Law

Concept review…Population genetic

Gene pool concept

Hardy-Weinberg

Law

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

a) Hardy-Weinberg lawa) Hardy-Weinberg law- State the Hardy-Weinberg lawState the Hardy-Weinberg law- Explain five assumptions of Hardy –Weinberg Explain five assumptions of Hardy –Weinberg

Law for genetic equilibrium:Law for genetic equilibrium:i.i. Large population sizeLarge population sizeii.ii. Random fertilizationRandom fertilizationiii.iii. no net mutationno net mutationiv.iv. no migration (include genetic drift)no migration (include genetic drift)v.v. no natural selectionno natural selection

b) Calculate allele and genotype frequenciesb) Calculate allele and genotype frequencies

The Hardy-Weinberg equilibrium

In 1908, G. H. Hardy (an English mathemathician) & W. Weinberg (a German physician) independently identified a mathematical relationship between alleles and genotypes in

populations. This relationship has been called

the Hardy-Weinberg equilibrium and it concerns allele frequency

Hardy-Weinberg LawThe principle that frequencies of alleles and genotypes in a population remain constant

from generation to generation,

Hardy-Weinberg Law Condition of a population for Hardy-Weinberg

equilibrium very large population size so that genetic drift

can be avoided (chance fluctuation in the gene that can cause phenotype frequencies to change over time).

no migration that cause gene flow due to immigration into or emigration out from the population

no net mutations because mutation may change an allele into another & this changes allele frequencies

random fertilization because if individuals choose mates only with certain traits, frequencies of certain alleles may change

All individuals must be equally fertile and able to pass the alleles to the next generation so that no natural selection is taking place

Hardy-Weinberg Law.

Related to allele frequencies are the genotypic frequencies

Genotype frequency is the ratio of number of individuals with certain genotype in a population

Hardy-Weinberg equations are used to estimate the frequencies of alleles & genotypes in a population which is in genetic equilibrium

Hardy-Weinberg Equations

Hardy-Weinberg Law. • The equations:

p2 + 2pq + q2 = 1 and p + q = 1

• p2 = genotypic frequency of homozygous dominant

• 2pq = genotypic frequency of heterozygous

• q2 = genotypic frequency of homozygous recessive

• p = frequency of dominant allele

• q = frequency of recessive allele

Hardy-Weinberg Equations

Hardy-Weinberg Law. Question 1• Resistance toward a type of pesticide for a population of rats is

controlled by dominant allele, R. 64% of the rat population show the resistance.

a) Calculate the frequency for R allele. Assume that the population is in genetic equilibrium and

p2 + 2pq + q2 = 1 while p + q = 1

36% of rat population are homozygous recessive (rr). Genotypic frequency for homozygous recessive (rr), q2 = 0.36

Frequency for recessive allele (r), q = √0.36 = 0.6

Frequency for dominant allele (R), p = 1 - q = 1 – 0.6 = 0.40.4

Example of calculation

Hardy-Weinberg Law. b) Calculate the number of rats with genotypes RR, Rr and rr for

a population of 200 rats. It is already known that p = 0.4 and q = 0.6

Genotypic frequency for homozygous dominant (RR), p2 = (0.4)2

= 0.16 Number of rats with genotype RR = 0.16 x 200 = 3232 Genotypic frequency for heterozygous (Rr), 2pq = 2(0.4)(0.6) = 0.48 Number of rats with genotype Rr = 0.48 x 200 = 9696 Genotypic frequency for homozygous recessive (rr), q2 = 0.36 Number of rats with genotype rr = 0.36 x 200 = 7272

Example of calculation

Hardy-Weinberg Law. Question 2• For a population of Shorthorns, the following data was

obtained:

Calculate the frequencies for alleles CM and CP.

Total number of individuals for the population = 308 Frequency for allele CM = 2(110) + 150 2(308) = 0.60.6 Frequency for allele CP = 2(48) + 150 2(308) = 0.40.4

Examples of calculation

Genotype Phenotype Number of individuals

CMCM red 110

CMCP red & white 150

CPCP white 48

Sekilas pandang…

Thank you for your attention