Population Genetics

2200 population genetics

I want to make sure we understand what we're doing here

For the Hardy-Weinberg equilibrium problems we are only dealing with one Mendelian trait.

E.g. pea plant height: 2 phenotypes (tall/short); 3 genotypes (TT, Tt, tt)

Multiple Choice

If no forces of evolution are acting (i.e. no gene flow, no gene drift, no mutation, and no natural selection, what should the following population's gene pool look like in the next generation?

p=0.6; q=0.4

• the exact same

• the reverse of what it is in this generation

• we have no way to predict

• all will be tall

Hardy-Weinberg equilibrium

• 1.We figure out what the allele frequencies are right now.

  2.Define EXPECTED genetic distribution if no evolutionary change were occurring

  2.We then RECORD the actual genetic distribution in the population

  3.If what we OBSERVE, differs from what we EXPECT, evolution is occurring

• For example: if we started out with p=0.5 and q=0.5 in the gene drift, we EXPECT it to always be 0.5/0.5.

• If this changes to 0.6/0.4, then evolution is occurring.

We use the equation to predict what the next generation should look like in order to detect evolutionary change

• p and q together are the gene pool

We're dealing with allele frequencies and genotype frequencies

• Genotype frequencies are a function of allele frequencies

• p + q = 1

• p² + 2pq + q² = 1

Multiple Choice

p = ________

• the dominant allele

• the frequency of the dominant allele

• the dominant genotype

• the recessive allele

Multiple Choice

If p = 0.2, then q = _______?

• 0.2

• 0.4

• 0.6

• 0.8

Multiple Choice

Why does p and q = 1

• because there are only 1 of each

• because the genotypes are different

• because all of the dominant alleles and all of the recessive alleles equal all of the copies of the gene

Multiple Choice

Pea plants: If I add up all the T alleles and all of the t alleles, do I have all of the copies of the gene?

• yes

• no

Multiple Choice

How many copies of the gene are present in 500 individuals?

• 250

• 500

• 1000

• 5000

Multiple Choice

Why does p² +2pq +q² = 1?

• because all of the dominant and recessive alleles add up to 1

• because all of the different genotypes add up to 1

• because there are no heterozygous individuals

All 3 genotypes add up to 100% because there are only 3 genotypes. (All the TT, Tt, and tt pea plants are all the pea plants)

Both phenotypes (e.g. tall and short) ALSO add up to 100% because there are only 2 phenotypes

Multiple Choice

From allele to genotype:

If q = 1, then ______

• half of the plants will have the recessive trait

• 100% of the plants will have the dominant trait

• 100% of the plants will have the recessive trait

• we don't have enough information to know whether the plants will have the dominant or recessive phenotype

The p and the q are the likelihood of passing the dominant or recessive allele in the population.

p2 + 2pq + q2 are the likelihood of those alleles coming together in the population

Multiple Choice

If p = 0.5, then p² = _______?

• 0.1 (or 10%)

• 0.25 (or 25%)

• 0.5 (or 50%)

• 1 (or 100%)

Multiple Choice

If 36% of the pea plants are homozygous dominant, what is p?

• p = 0.36

• p = 0.6

• p = 0.64

• not enough information

If 36% of the population is homozygous dominant--that's p²=0.36.

We figure out 'p' by taking the square root of 0.36.

Therefore, p=0.6. Once we know one allele frequency we know the other.

All dominant alleles plus all the recessive alleles must equal 100% of the alleles (all T + all t = 100%)

The frequency of dominant alleles plus recessive alleles must equal 1 (p + q =1).

For phenotype, all of the dominant and recessive traits must equal 100% (all tall + all short = 100%)

All of the homozygous dominant, heterzygous and homozygous recessive must add up to 100% (p² + 2pq + q² = 1)

Multiple Choice

If we know that 75% of the plants are tall, then

• p2 must equal 0.75

• p must equal the square root of 75

• 25% of the plants must be short

• all of these

Multiple Choice

In the last question, I said that 75% of the pea plants were tall. What are we looking at here?

• dominant allele

• homozygous dominant genotype

• dominant phenotype

• heterozygous genotype

Multiple Choice

The 75% of those plants that are tall include ____.

• individuals of all three genotypes

• all the homozygous dominant genotype

• all the heterzygous genotype

• all the homozygous dominant and heterozygous genotype