Population Genetics & Hardy - Weinberg

Remember Microevolution: Examines the evolutionary changes that lead to changes in traits within a population or species Population Genetics: studies the changes in the numbers & types of alleles in a population Examines changes to the genes (alleles) within populations Small changes that do not lead to new species, but can lead to new variations (traits). Examines how changes in a population can impact the whole species

Hardy- Weinberg Principle Evolution will not occur in a population unless outside forces act upon allele frequencies.

5 conditions must be met in order for NO change to be seen in a population (i.e. equilibrium) NO mutation NO migration Population is infinitely large There is random mating Selection does not occur

Violations to the 5 conditions? Based on what your learned yesterday, can you identify any violations to these rules? Condition: No mutations Violation: Mutations happen and new traits can be added to the population

Condition: No Migration Violation: As organisms move from one population to another, their genes move with them

Condition: Random Mating Violation: Sexual Selection If parents are selective (picky) or limited in their choice of mates, only a limited set of traits will be passed on.

Condition: Infinitely Large Population Violation: Genetic Drift Founder’s Effect

Condition: Natural Selection Does Not Occur Violation: Natural Selection does occur Changes in environmental pressures can cause an increase or decrease in certain alleles (traits) in a population

How can we tell if populations are evolving? Hardy- Weinberg How can we tell if populations are evolving? Hardy Weinberg Mathematicians who developed formula to determine if populations are evolving.

p + q = 1 The equations: p2 + 2pq+ q2 = 1 Allows us to determine the equilibrium frequency of each genotype in the population. P: represents the dominant allele Q: represents the recessive allele p2 :represents homozygous dominant 2 pq :represents heterozygotes q2 : represents homozygous recessive

Let’s Practice: On your whiteboard . . . What is the symbol for the allele frequency of the homozygous recessive individual? What is the symbol for the allele frequency of the heterozygous individual? What is the allele frequency of the homozygous dominant individual? q2 2pq p2

On your whiteboard, what is the symbol for the dominant allele If the allele frequency of r is .75 what is the allele frequency of R? p + q = 1 r = q so p + .75 = 1 p = .25

What is the frequency of the dominant allele? Tay- sachs disease is caused by a recessive allele. The frequency of the allele is .1 of a population of 3,600. What is the frequency of the dominant allele? How many in the population will have Tay- Sachs? How many in the population are carriers? p + .1 = 1 p = 1-.1 = 0.9 q2 = (.1)2 * 3600 q2 = 36 2pq = 2(.1 *.9) * 3600 648 = 2 pq

B. The frequency of the "a" allele. You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following: A. The frequency of the "aa" genotype. B. The frequency of the "a" allele. C. The frequency of the "A" allele. D. The frequencies of the genotypes "AA" and "Aa." E. The frequency of showing the dominant phenotype in the population & the frequency of showing the recessive phenotype in the population.

A. Homozygous recessive = 36% = 36/100 = .36 = q2 B. q = .𝟑𝟔 =𝟎.𝟔 C. p + .6 = 1 p = 1- .6 = .4 D. p2 = .42 = .16 2 pq = 2 (.6)(.4) = .48 E. Dominant phenotype: p2 + 2pq = .16 + .48 = .64 Recessive phenotype: q2 = .36

Hardy- Weinberg Challenge In your groups, complete the Hardy- Weinberg worksheet. When you are finished bring it to me to check. If your group has answered all questions correctly there is a prize. Once I have checked your work you may begin on your homework.