Process of Evolution

Wednesday, February 18th What do you think the term microevolution means? What do you believe some of the causes for microevolution are?

Monday, February 23rd In a population, if no mutations occurred in the individuals what do you think would happen in the gene pool of the succeeding generations?

Tuesday, February 24th If a population if 36% of the individuals are homozygous dominant, what % of the population has the recessive phenotype, assuming Hardy- Weinberg equilibrium?

See your notes if you don’t remember the 5 conditions! Wednesday, February 25th Of the 5 conditions of H-W equilibrium, which could cause the greatest change in a population if it were applied? Why? See your notes if you don’t remember the 5 conditions!

Thursday, February 26th In natural selection, there are three types of selection that occur, one of those being directional selection. What do you think is occurring in a population with this type of selection.

Friday, February 27th Would you like the idea of preparing for the AP test outside of class? What days and times would you be willing to attend?

Evolution in a Genetic Context Darwin knew that members of a population varied but he did not know how variations came about and they were transmitted in populations Around the 1930s, geneticists were able to apply concepts of genetics to Darwin’s idea of populations We now recognize this as a way that evolution has occurred

Population: all members of a single species occupying a particular area at the same time Microevolution: Evolution that occurs within a population Population Genetics: study of gene frequencies in and their changes within a population Gene Pool: total of all genes of all the individuals in a population

Allele Frequencies It is customary to describe the gene pool of a population in terms of gene frequencies To calculate the frequency of each allele, you must have the # of each genotype (homo dominant, heterozygous, homo recessive) & the total # of individuals of a population

What is the number of the allele R and the allele r in the population? Suppose in a Drospholia (Fruit Fly) population, 1/4 of the flies are homozygous dominant for red eyes, 1/2 are heterozygous and 1/4 homozygous recessive. There are a total 100 individuals in the population. What is the number of the allele R and the allele r in the population?

Hardy-Weinberg Law p2 + 2pq + q2 Because of the result of calculating the frequency of alleles, we can determine that sexual reproduction ALONE cannot bring about change in a gene pool G.H. Hardy (English Mathematician) & W. Weinberg (German Physician) recognized the potential constancy, or equilibrium state, of gene pool frequencies Used a binomial expression to calculate the genotypic and allele frequencies of a population Hardy-Weinberg Equation: p2 + 2pq + q2

p+q=1 (Sum of frequencies in both alleles is 100%) p2 = % homozygous dominant individuals (AA) p = frequency of dominant alleles q2 = % homozygous recessive individuals q = frequency of recessive allele 2 pq = % heterozygous individuals p+q=1 (Sum of frequencies in both alleles is 100%) p2+2pq+q2=1

H.W Law states that equilibrium of allele frequencies in a gene pool, will remain in effect in each succeeding generation of a sexually reproducing population as long as 5 conditions are met

5 conditions: No Mutations: allelic changes do not occur, or changes in one direction are balanced by the changes in the opposite direction No Gene Flow: migration of alleles into or out of the population does not occur Random Mating: individuals pair by chance and NOT according to their genotypes and phenotypes No Genetic Drift: the population is very large , and changes in allele frequencies due to chance alone are insignificant No Selection: no selective agent favors one genotype over another

Why is H-W Law Important? Provides a baseline by which we can judge if evolution has occurred In life, the 5 conditions for maintaining equilibrium of allele frequencies, are rarely met if ever; hence the fact we have genetic variation Any change of allele frequencies in the gene pool of a population signifies evolution has occurred

Calculating Gene Pool Frequencies using H-W 16% of the human population has a continuous hairline (recessive trait). Using this information complete all the allele and genotypic frequencies for the population. Assuming H-W equilibrium conditions are met.

Where do we start?

SOLVE!

What percentage of the population will have the dominant phenotype What percentage of the population will have the dominant phenotype? Recessive?

H-W Lab: Case #2 Recall the five requirements of H-W equilibrium For your row (Labels for each row are placed at the front), describe how you will modify that H-W requirement, so that it no longer applies to your experiment Next, draw out another data just as you did yesterday; label this graph as “Out of Equilibrium”

3. Take your pre-sorted cup of alleles, decide which color will be dominant and which will be recessive 4. Record the number you have of each allele (ex. 25 - B, 35 - b) 5. Using the H-W equation, do the % of dominant alleles and recessive alleles in the population (ex. 25/100 = 25%) 6. Apply the modification you came up with to your population (ex. Having no random mating, you would specifically pick out the genotypes you want) 7. Perform 5 generations, as you did yesterday, record your data

8. Compare the results you got in your group to another groups results 8. Compare the results you got in your group to another groups results. Similarities? Major differences? 9. Answer the questions for each Case Study (#1 and #2). 10. Turn in your data tables, graphs and answers to your questions. 11. Once you finish with the lab, you can work on the H-W Practice Problems I gave you for HW this week and the Post-Learning portions for your journals! 