BLG 144 Lecture Notes - Lecture 5: G. H. Hardy, Genotype Frequency, Allele Frequency

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27 Apr 2018

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CHAPTER 25 - EVOLUTION

Four evolutionary mechanisms that causes evolution and affects populations :

1. Natural Selection – increases frequency of those alleles that contribute to reproductive success

2. Genetic drift – causes allele frequencies to change randomly

3. Gene flow – when individuals leave one population, join another, and breed

4. Mutation – modifies allele frequencies by continually introducing new alleles

1,2, and 3(within a population) – reduces genetic diversity

3 ( between populations, immigration) and 4 – increases genetic diversity

Hardy-Weinburg Principle

- 1908, Godfrey Harold hardy and Wilhelm Weinburg developed a mathematical model to analyze

the consequences of mating among all of the individuals in a population

- They imagined all of the gametes produced in each generations go into a single group called a

gene pool and combine randomly

- Their results predicted the kinds of genotypes and the frequency of offspring that the

population would produce

- Had 2 variables and made a punnett square. Results gave them p, q, pq and pq giving them the

equation p2 +2pq+q2 = 1 (Hardy-Weinburg equation)

- The Hardy-Weinburg principle fundamental claims:

1. If the frequencies of alleles A1 and A2 in a population are given by p and q, then the

frequencies of genotypes A2A1, A1A2, and A2A2 will be given by p2, 2pq and q2…. For

generation after generation.

2. When alleles are transmitted via meiosis(crossing over) and random combination of

gamete(independent assortment), their frequencies do not change over time.

3. For evolution to occur, some other factor or factors must come into play

- Assumptions you need when using Hardy-Weinburg Model

1. No natural selection, no genetic drift or random allele frequency changes, no gene flow,

no mutation, and there is random mating

- The Hardy-weinburg principle functions as a null hypothesis to see if natural selection acts on a

particular gene, non-random mating is occurring,or if one of the other evolutionary mechanisms

is at work

- When genotype frequencies do not conform to Hardy-Weinburg proportions, either evolution or

non-random mating is occurring in that population

- Testing MN Blood Types

1. Estimate genotype frequencies

2. Calculate observed allele frequencies from the observed genotype frequencies

3. Use the observed allele frequencies to calculate the genotypes expected according to

the Hardy-Weinburg principle

4. Compare the observed and expected values

- Hardy-Weinburg principle is used to test if there is no evolution at a particular gene and that the

previous generation, mating was random with respect to the gene in question

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Document Summary

1,2, and 3(within a population) reduces genetic diversity. 3 ( between populations, immigration) and 4 increases genetic diversity. 1908, godfrey harold hardy and wilhelm weinburg developed a mathematical model to analyze the consequences of mating among all of the individuals in a population. They imagined all of the gametes produced in each generations go into a single group called a gene pool and combine randomly. Their results predicted the kinds of genotypes and the frequency of offspring that the population would produce. Had 2 variables and made a punnett square. Results gave them p, q, pq and pq giving them the equation p2 +2pq+q2 = 1 (hardy-weinburg equation) If the frequencies of alleles a1 and a2 in a population are given by p and q, then the frequencies of genotypes a2a1, a1a2, and a2a2 will be given by p2, 2pq and q2 .

Related Questions

Q1. What is the founder effect?

Sampling error that occurs during the establishment of a newpopulation by a small number of migrants.

Strong natural selection acting on the founders of a newpopulation because the environment they are now living in is sodifferent from the environment they came from.

A phenomenon named after William Founder, who observed that toppredators generally have low genetic diversity.

Rapid population growth following a bottleneck.

Q2. The effects of genetic drift are more pronounced in largerpopulations.

True

False

Q3. Inbreeding tends to increase the proportion of homozygousindividuals in a population (i.e. individuals that have two copiesof the same allele).

True

False

Q4. The effective size of a population is:

The size of an idealized randomly-mating population that is notunder selection and has the same heterozygosity as the actualpopulation.

The size of an idealized randomly-mating population that has thesame heterozygosity as the actual population, but does not loseheterozygosity over time.

The size of an idealized randomly-mating population losinghomozygosity at the same rate as the actual population.

The size of an idealized randomly-mating population losingheterozygosity at the same rate as the actual population.

Q5. Which of the following tends to reduce the effective size ofa population?

Check all that apply:

Increasing the population size.

A biased sex ratio.

Non-random mating.

Q6. If gametes from a gene pool combine randomly to make only asmall number of zygotes, the allele frequencies among the zygotesmay be different than they were in the gene pool because:

The effects of natural selection are more pronounced in smallpopulations.

The effects of genetic drift over several generations are morepronounced with small numbers of gametes.

The effects of differences in frequencies for different allelesare more pronounced with small numbers of zygotes.

The effects of sampling error are more pronounced with smallsamples.

Q7. Genetic drift is different from natural selectionbecause:

In natural selection allele frequencies change because somealleles confer higher fitness, whereas in genetic drift allelefrequencies change because of chance sampling error.

Natural selection acts primarily in large populations, whereasgenetic drift acts primarily in small ones.

Natural selection is a mechanism of evolution, whereas geneticdrift is an outcome of evolution.

Natural selection tends to cause rapid evolution, whereasgenetic drift tends to cause slow evolution.

Q8. Imagine a population evolving by genetic drift in which thefrequency of allele K is 0.65. What is the probability that at somepoint in the future allele K will drift to a frequency of 1?

Q9. A dwindling population of 1000 frogs occupies an isolatedwatershed in Costa Rica. To help preserve the species, scientistscaught 20 frogs to start a new population in a nearby watershed.This species has a gene that affects eye shape. The 1000-memberwild population has two alleles for this gene: R and r, withfrequencies 0.7 and 0.3, respectively. What will be the allelefrequencies of R and r in the 20-member founder population?

The frequencies will be 0.7 for R and 0.3 for r.

The frequencies will be 1.0 for R and 0 for r.

The expected frequencies are 0.7 for R and 0.3 for r. The actualfrequencies could be different.

The founder populations's allele frequencies will necessarily bedifferent than the source population's frequencies.

Q10. For a population containing 90 females and 10 males, whatis the effective population size, N_e ?

chocolateplatypus914

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.

indigosnake469

1) Which of these probabilities are NOT independent of eachother?

The probability that a student is a sophomore and has brownhair

The probability that when you roll two dice, you will roll a 6before a 2

The probability that it will rain and the probability ofneeding an umbrella

The probability that there will be heavy traffic on BaltimoreAve and the probability you will lose your cell phone

2) We are defining evolution as a "change in allele frequenciesover time". Ironically, the focus of this lab is the Hardy-Weinbergequilibrium - conditions that, if all met, will result in NOevolution occurring. Which of the following are among theconditions that must be met for the Hardy-Weinberg equilibrium toapply perfectly to a population?

A. The population must be very large

B. Individuals must mate at random

C. The alleles must differ in their effects on survival

D. There must be free migration into and out of thepopulation

A & B

A, B, & C

3)In cats, black fur is dominant over any allele for brown fur.If a homozygous dominant cat makes kittens with a heterozygous cat,what is the probability that the first kitten will have brown fur?Report as a proportion, not percentage, e.g., .1, NOT 10%.

The EGLN1 gene helps regulate body oxygen levels. One allele His dominant over h, and helps increase fitness at high altitude(where oxygen is low). In a study of families in Tibet, researchersfound 422 HH individuals, 377 Hh, and 201 hh individuals. The studyshowed that infant mortality was lower in Hh individuals than hh,and lowest in HH individuals.
Is the Tibetan population in Hardy Weinberg Equilibrium at this H/hgene?

What is the most important factor affecting the strength ofgenetic drift?

The frequency of the rarest genotype

The size of the population

The allele frequencies

The genetic diversity in the population

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BLG 144 Lecture Notes - Lecture 5: G. H. Hardy, Genotype Frequency, Allele Frequency

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