Population Genetics“The study of genetic variation and its causes in

population”

Suggestion to do well in this class

# Attend every lab session. # Give your undivided attention. # Ask the TA to repeat himself.# Review the power-point presentations before the quiz.# Hand your assignment in due time.# Do your best with the lab. reports

Announcements

• Cedo field trip.• preceptor program• Home assignment include game 1, 2, and questions 1, 3 and 4 on page 12•There will be a quiz (8 points) on Thursday, February 3th. The questions will cover materials from the population genetics lab and the classification and phylogeny lab.

Population Genetics

• Evolution

• Mechanisms of evolution

• How to prove it

• How to measure evolution

Evolution • Population is a group of individuals that

coexist in certain place at the same time and capable of interbreeding with one another

• Evolution is change over time in the traits of a population

• Phenotype is the observable properties of an organism.

• Gene is piece of DNA that codes for a protein

• Alleles are different forms of a gene

Evolution• Genotype is the genetic composition the governs a trait (AA, Aa, aa)• Evolution is change of the allele frequencies over time.• Dominant allele, determine the phenotype of heterozygous individuals.•Recessive allele, shows its phenotype only in homozygous individuals

Forces of evolution• Natural selectionadvantage in survival and reproduction.• Mutations.random changes in nucleotide sequence.• Migration (gene flow).new individuals are introduce to the population. • Non-random mating.possession or absence of certain phenotype.• Genetic drift.random changes (allele fixation in small population).

Natural selection

Genetic drift

Genetic drift

• Its effect is clear in small populations

• These populations lose genetic variability rapidly.

• alleles drift to fixation.

• http://darwin.eeb.uconn.edu/simulations/drift.html.

Gene flow

Applied aspects of population genetics

Cystic fibrosisCystic Fibrosis (CF) is the most common AR (autosomal recessive) disorder found in Caucasians with an estimated incidence of 1 in 2500 in newborns of European ancestry. About 1 in 25 persons of European ancestry is a carrier.CF especially affects the respiratory and digestive systems. The CF gene was identified in 1989. The average life expectancy of a person with CF is now at 30 years, due to advances in medical care.

Evolution

How to prove that evolution occur

• Hardy-weinberg theory (equilibrium)

A population that is not changing genetically from generation to generation.(null hypothesis)

• Essential assumptions

1-Mating is random

2-Population size is very large (no effect for genetic drift)

3-Mutations can be ignored

4-Natural selection has no effect

5-No migration

Hardy-weinberg theory (equilibrium)

A a

A

a

sperm

eggs

AA Aa

Aa aa

Punnett square

Frequency of event= actual number of occurrence total number of events

Hardy-weinberg theory (equilibrium)

Allele frequency = number of occurrence of that allele total number of alleles in the population Genotype frequency= number of occurrence of that genotype total number of the population or product of its alleles frequency= p * q

Note: frequency is just another way to express (absolute)numbers. It is just the decimal fraction

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

How to measure evolution Calculate allele and genotype frequencies in each generation and compare it to the previous one. are differences in genotype frequency from generation to generation evident? Are we sure that these differences have not happened due chance alone?Significance of the difference in frequency chi-square analysis ( X2 ) P.200

X2 = (O # – E# )2

E# X2 = 0 it is hardy-weinberg equilibrium ( H0 or null hypothesis)The higher the value of X2, than that obtained by chance, the more likely to be significant

How to measure evolution

Degree of freedom : number of categories that are free to vary indepenantly .

df = total number of categories - 1

Questions

1a- population in game 21b- for game 2, we have high confidence because the probability of sampling error were less than 5% . For game 1, vice versa..1c- population in game 11d- population in game 2 because evolutionary force (natural selection) was acting in the population.3a- by natural selection3b-heterozygous individuals4- aa= 0.7x 0.7=0.49 AA=0.3x0.3=0.09 Aa=0.3x0.7=0.21 = 0.21x2=0.42