Populations

Question 1

Define gene pool

Answer 1

All the alleles in a population

Question 2

Define allele frequency

Answer 2

How often an allele occurs in a population.

Usually given as a percentage of the total population, e.g. 35%, or a decimal, e.g. 0.35.

Question 3

What does the Hardy-Weinberg principle predict?

Answer 3

The frequency of alleles (of a particular gene);

Will stay constant from one generation to the next / over generations

Providing there are no mutations / no selection / population large / population genetically isolated / mating at random / no migration;

Question 4

Hardy Weinberg equation
for allele frequency

Answer 4

p + q = 1

p is the frquency of one allele (usually dominant)
q is the frequency of the other allele (usually recessive)

Question 5

If the frequency of a dominant allele is 0.72, what is the frequency of the recessive allele?

Answer 5

p + q = 1.0

0.72 + q = 1.0

q = 0.28

Question 6

Hardy Weinberg equation
for genotype frequency

Answer 6

p^2+2pq+q^2=1

Where:
𝑝2: Frequency of the homozygous dominant genotype

2pq: Frequency of the heterozygous genotype

𝑞2: Frequency of the homozygous recessive genotype

Question 7

For a gene with two alleles, B and b. Consider a population of 1000 people, where 300 are homozygous dominant (BB), 500 are heterozygous (Bb) and 200 are homozygous recessive (bb).

Calculate the allele frequency of B and b.

Answer 7

The total number of alleles is: 1000 x 2 = 2000

The number of B alleles: (300 x 2) + (500 x 1) = 1100
Frequency of the B allele: 1100 / 2000 = 0.55

The number of b alleles is: (200 x 2) + (500 x 1) = 900
Frequency of the b alleles: 900 / 2000 = 0.45

p + q = 1.0
0.55 + 0.45 = 1.0

Question 8

The scientists concluded that the observed frequencies of the phenotypes differed significantly from the expected frequencies.

Use your knowledge of the Hardy–Weinberg principle to suggest two reasons why.

Answer 8

Selection (against/phenotype/allele);
(High rate of) mutation;
Immigration/emigration;
No random mating.

Question 9

In mice, one type of disease is inherited as a dominant allele. Would the Hardy–Weinberg principle hold true for a population of mice, some of which had this disease?

Explain your answer

Answer 9

(No)
1. Mice with disease will be unlikely
to reproduce/survive
OR Mice with disease will be selected against;

2. Will not pass on allele (for disease)
   OR Allele frequency (for disease) will reduce;

(Yes)
3. As long as the disease did not
affect the mice’s ability to reproduce/survive;

4. The allele frequency will remain constant/not
   change;

Question 10

A population of fruit flies contained 64% grey-bodied flies (Genotype is GG or Gg).

Use the Hardy–Weinberg equation to calculate the percentage of flies heterozygous for gene G.

Answer 10

48%