Population Genetics - MCB 104

Question 1

Why is population genetics important?

Answer 1

population genetics determines how often does a variation occur in population (frequency) which then helps to define a population.

Question 2

How does population genetics study variation?

Answer 2

First they came up with an idea of “ideal population” that fulfills several assumptions.

Then they examine what happens when each of these assumptions is violated one by one

Lastly they examine how these variations change in time and space in natural non-ideal populations

they go from simplified to a consecutively hard model (the model that describes the real population)

Question 3

How do scientists calculate genotype frequencies?

Answer 3

count the number of individuals of each genotype in a sample and then divide the number of individuals in the population.

Question 4

For some traits, it is not possible to count individuals that carry a particular genotype. For example, if for blue eye traits:
aa = blue eyes
AA = dark eyes
Aa = dark eyes

here hetero and homo both give rise to dark eyes.

How do scientists predict genotype frequencies in such a situation?

Answer 4

by using a molecular assay

Question 5

There are 20 individuals, 16 with dark eyes and 4 with blue eyes. dark eye is dominant to blue eyes.
DNA analysis showed that 12 out of 20 are AA, 4 are Aa and 4 are aa. Find the frequencies genotype and allele.

Check explanation on page 664 last para before allele frequency begins

Answer 5

Genotype frequencies:
AA = 0.6
Aa = 0.2
aa = 0.2

Allele frequencies:
A = 0.7
a = 0.3

Question 6

What is the formula to calculate Allele frequencies if you forget how to do it logically?

Answer 6

Frequency of allele A = frequency of AA + 0.5 * frequency of Aa

Frequency of allele a = frequency of aa + 0.5 * frequency of Aa.

Question 7

So what was the Hardy Weinberg generation - generation assumption? and how did they use correlation between genotype and phenotype frequency to substantiate their Law?

Answer 7

• if certain assumptions were met, allele frequencies, genotype frequencies, and phenotype frequencies would remain the same over time between generations.
• p^2 + q^2 + 2pq = 1

Question 8

And what were the assumptions that should be met?

Answer 8

1. That the population is composed of a very large number of diploid individuals, i.e the population is infinite.
2. individual’s genotype has no influence on his/her choice of mate - mating is always random.
3. No new mutations appear in the gene pool
4. no migration of individuals occurs
5. different genotypes have no impact on fitness.

Question 9

What is the Hardy Weinberg Equilibrium and when does a population reach HWE?

Answer 9

that allele and genotype frequencies for a locus will not change unless one of the assumptions is violated.

when a population is a reasonably close fit to the assumptions and the allele frequencies will not change over time only genotype frequencies will change briefly to reach proportions predicted by the frequencies.