5.0 POPULATION GENETICS

1. 5.0 POPULATION GENETICS 5.1 Gene pool concept 5.2 Hardy-Weinberg Law BY: NUR HIDAYAH MUHAMAD SALEH

2. 5.1 Gene pool concept At the end of this topic, students should be able to: • Explain population genetics, gene pool, allele frequency and genetic equilibrium.

3. 5.1 Gene pool concept • Population • Defined as individuals of the same species that live in the same locations that can freely interbreed and produce fertile offspring in nature. • Exhibit variation in traits. • Population genetics • The study of genetic variation within a population. • Population genetics is concerned with determining the genotype frequency and the allele frequency.

4. 5.1 Gene pool concept • Gene pool • Total number of all alleles at all the gene loci in all individuals of the population at a given time.

5. 5.1 Gene pool concept Take for example: A population consists of 27 individuals. In this population, a particular character is controlled by a certain gene. Two alleles involved for each gene. Assume that among 27 individuals, 9 have genotype A1A1, 9 have genotype A2A2and 9 have genotype A1A2. What is the gene pool of this population?

6. 5.1 Gene pool concept • Allele frequency • refers to how frequently a particular allele appears in a population • In general, allele frequency can be defined as: Frequency of allele A: Total number of copies of allele Ainpopulation Total number of all the alleles in the gene pool

7. 5.1 Gene pool concept • Genotype frequency • Refers to how frequently the individual with certain genotype appears in a population. • Can be defined as: Frequency of genotype AA: Total number of individual withgenotypeAA Total number of all individual in the population • Genetic equilibrium • A condition where an allele or genotype frequency in a gene pool does not change from generation to generation.

8. 5.2 Hardy-Weinberg law At the end of this lesson student should be able to: • State the Hardy-Weinberg Law • Explain five assumptions of Hardy-Weinberg Law for genetic equilibrium: • Large population size • Random mating • No mutation • No migration • No natural selection

9. 5.2 Hardy-Weinberg law • In 1908, G.H Hardy (an English mathematician) and W.Weinberg (a German physician) independently described a basic principles of population genetics. • This principles had been named the Hardy-Weinberg equilibrium and it concerns alleles frequency and genotype frequency.

10. Hardy-Weinberg Law states that: • the frequency of alleles and genotypes in a population will remain constant • from one generation to the next generation • provided certain conditions are met. In other words it means that: • If a population is not evolving it is in genetic equilibrium and the alleles frequency do not change. • If a population evolve, the alleles frequency in the population will change.

11. 5.2 Hardy-Weinberg law The five assumptions of Hardy-Weinberg Law: • Large population size • Random mating • No mutation • No migration • No natural selection The allele and genotype frequency in a gene pool will remain constant if all of these conditions are met.

12. five assumptions of Hardy-Weinberg Law 1. Random mating • Each individual in a population has an equal chance of mating with any individual of the opposite sex. • Each individual must mate at random and must not select their mates on the basis of genotype or any other factors that result in non-random mating.

13. five assumptions of Hardy-Weinberg Law 2. No mutation • There must be no mutations that convert the allele ( i.e. A into a or vice versa). • The allele frequencies must remain the same. 3. No migration • The population is isolated. There can be no migration of individuals into or out of the population.

14. five assumptions of Hardy-Weinberg Law 4. Large population size • So that any changes in allele frequency is negligible. 5. No natural selection • All individual are equally likely to survive and reproduce. All alleles have equal fitness and advantage to be favored by the environment.

15. Hardy-Weinberg Equation • Hardy and Weinberg went on to develop simple equation that can be used to discover allele frequency and genotype frequency in a population. p + q = 1 p2 + 2pq + q2 = 1

16. Hardy-Weinberg Equation For a gene locus of diploid species where only two alleles occur in a population, we use : p : frequency of dominant alleles (A) q: frequency of recessive alleles (a) Because there are only two alleles, the frequency of one plus the frequency of the other must equal 100% Allele Frequency: p + q = 1

17. Hardy-Weinberg Equation p2 = frequency of homozygous dominant genotype (AA) q2 = frequency of homozygous recessive genotype (aa) 2pq = frequency of heterozygous genotype (Aa) Genotype Frequency: p2 + 2pq + q2 = 1

18. Law to obey • Determine the type of information. They may be in the form of: - number of individuals - percentage - ratio - fractional - total number of allele

19. Law to obey • Firstly, Identify any information of recessive traits • NEVER START calculation with information of dominant trait. • If allele frequency is required, answer should be either in the form of : • p (dominant) • q (recessive)

20. Law to obey • If genotype frequency is required, answer should be either in the form of : • p2 • q2 • 2pq • If number of heterozygous individual or the carrier is required, answer should be • 2pq x number of individual • If number of individual with dominant phenotype is required, answer should be: • (p2+ 2pq) x number of individual

21. Law to obey • If heterozygous or carrier frequencies is required, answer should be : * 2pq • If percentage of heterozygous or carrier is required, answer should be : * 2pq x 100%

22. Example Question : Number of individual • In a population of 350 students in a collage, only 50 students are non-taster for PTC. Calculate the frequency allele of the non-taster and find the number of student who are heterozygous for this trait?

23. Example Question : Percentage • Albinism in mice is a recessive allele due to a mutant gene. In a population of mice, 16% are albino. Assume that the population is in the Hardy- Weinberg equilibrium, what is the frequency of carrier?

24. Example Question : fractional / ratio • In a maternity hospital, 8 out of 3200 babies were affected with heart disorder, which is governed by a recessive allele. Calculate the frequency of the carrier in the population.

25. Example Q : total number of allele Two allele T1 and T2 are present in a population at Hardy-Weinberg equilibrium. The numbers of different genotype in the population is shown below. Determine the total number of each T1 and T2 allele in the population.

26. Example 1 : A wildflower population with two varieties contrasting in flower color. An allele for pink flowers which is symbolize by A are completely dominant to an allele for white flower, symbolize by a . If the frequency of allele A is 0.8, what is the frequency of allele a? Example 2 : Calculate the frequency of heterozygous (Mm) in a random mating population if the total frequency of dominant phenotype is 0.19 Example 3 : In sheep, white wool is governed by dominant allele B and black wool by recessive allele b. From a population of 1200 sheep, 1188 are white and 12 are black. Determine the frequency of allele B and b.