BIOB51H3 Lecture Notes - Lecture 13: Allele Frequency, Gene Flow, Allele

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7 Jan 2018

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Slide 3: migration is the movement of alleles into the population, allele frequency can change after migration happens. Slide 4: gene flow transfer of alleles from gene pool of one population to gene pool of another population. Slide 6: migration from a small population to large population, it wont be that much of a big difference. Slide 7: effect of migration on island allele freq, p*i= (1-m)pi+ mpc. Slide 8: more different pi and pc are, the bigger the effect on island frequency. Also, the larger amount of people moving from place to place has an effect on island frequency as well. Slide 11: example 1: water snakes, snakes that can swim, they have very different morphologies (unbanded, strong banding patterns and variations in between) Slide 13: mainland means that the banded ones have higher fitness (ohio and ontario). Slide 14: a light grey, d heaviest banding, mainland there is selection on banding.

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A population of finches lives on an island some distance from the mainland, where another population of finches of the same species resides. In both populations, the size of the birds' beaks is influenced by two alleles at the beak locus, B and b. Finches with the BB genotype have the largest beaks, bb have the smallest beaks, and Bb individuals have a beak size intermediate between the two homozygotes. On the island, the frequency of the B allele is 0.3, and the frequency of the b allele is 0.7. On the mainland, both alleles are equally frequent (0.5).

(a) If the migration rate from the mainland to the island is 0.1 (meaning that 10% of individuals in the island population migrate in from the mainland every generation), what is the change in the frequency of the B allele on the island in one generation due to migration? Assume there is no migration from the island back to the mainland.

(b) The genotypes at the beak locus have the following fitness on the island: w_BB = 0.95, w_Bb = 0.98, w_bb = 1. Which allele is the most fit? What size beak is selectively favored on the island? What do you predict will happen to the frequencies of these alleles in the long term?

(c) The island experiences a severe drought for two consecutive years, which kills a plant species on the island that makes small seeds eaten by the finches. As a consequence, the food available decreases and the average size of edible seeds on the island increases greatly. Birds with large beaks are much better able to crack large seeds and thus better able to survive the drought. Which allele is the most fit? How do you predict the allele frequencies of B and b will change during this drought?

____________________________ create new alleles in a population.

The change in allele frequency in a population over time is ____________________, not macroevolution, which refers to the formation of new ____________________.

Name one assumption (condition) that a population must satisfy to remain in Hardy-Weinberg equilibrium.

___________________________________________________________________

____________________ is the movement of alleles from one population to another due to migration.

_____________________ is a random change in allele frequency and has the greatest effect on ____________________ (small or large) populations.

The _____________________ of a population, resulting from some population crash, will cause the entire loss of some alleles due entirely to chance.

A type of genetic drift, known as ________________________________________, can cause rare alleles to become âcommonâ in the population, such as polydactyly in the Olde Order Amish populations.

Females prefer to mate with males who express certain traits. This is known as ____________________ and requires the two sexes to have different appearances (known as: ____________________ ____________________).

Q1. What are alleles?Different forms of the same gene.Different genes.The different characteristics of an organism.Genes found only in humans.Q2. If you add up the frequency of homozygotes + the frequency of heterozygotes for one gene (i.e. at one locus) in a population, what number do you get?Q3. People who are heterozygous for the sickle-cell allele:Are susceptible to malaria but not sickle-cell anemia.Are susceptible to sickle-cell anemia but not malaria.Are not susceptible to either sickle-cell anemia or malaria.Are susceptible to both sickle-cecell anemia and malaria.Q4. In the case study in this lab, which genotype is represented by "2pq" in the Hardy-Weinberg equation?Homozygous HbAHomozygous HbSHeterozygous HbA/HbSNo specific genotypeQ5. Suppose that, in an isolated village, the proportion of individuals that have sickle-cell anemia is 0.1 (or 1 of every 10 people). What proportion of the population should be sickle-cell carriers, according to Hardy-Weinberg expectations?Q6. When you simulated the elimination of malaria at the beginning of the lab, once the allele frequencies stabilized, what was the frequency of the HbA allele?Q7. When you investigated regional differences, what was the frequency (over many generations) of the HbS allele in the village in the "slightly wet" part of Africa?Q8. What is the number of deaths due to sickle-cell anemia in a region without mosquitoes expected to be?Very lowVery highModerateRelated to the frequency of malaria allelesQ9. As long as there are multiple alleles of a gene in a population, why will the frequencies of the alleles always change over time?Because natural selection changes all allele frequencies in populations over time.Because genetic drift causes random fluctuations of allele frequencies in populations.Because diseases will eliminate some of the alleles, generating fluctuations in their frequencies.Because allele frequencies fluctuate before the alleles eventually become fixed.Q10. Imagine a huge population with a gene that has ten functionally equivalent, neutral alleles. A small but genetically representative group of individuals from the big population is transported to an island, forming a small population. Which of the statements below best describes what will likely happen over time, and why?Because natural selection doesn't act on neutral alleles, the frequencies in the two populations should remain the same over time.Genetic drift will cause one allele to first become fixed in the island population, and later to become fixed in the original, large population.Genetic drift will result in the allele frequencies of the two populations diverging over time, with alleles being lost sooner in the island population.The allele frequencies of the two populations will change similarly due to a combination of genetic drift natural selection.

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BIOB51H3 Lecture Notes - Lecture 13: Allele Frequency, Gene Flow, Allele

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