1. What is meant by the term "gene pool" ?
Answer
All the alleles of all the genes that are present in a population at a given time.
2. Give five assumptions that are made when using the Hardy–Weinberg equation.
Answer
Population is large, there is no immigration or emigration, mating is random, no genotype is selected for or against and there is no gene mutation.
3. Two co-dominant alleles, LM and LN, code for different proteins on the cell-surface membrane of red blood cells. The population of a country is 100842284, of which 27.8% were found to have the LMLM genotype. Using the Hardy–Weinberg equation, calculate the number of individuals in the population that are heterozygotes.
Answer
There are 50320300 individuals (or 49.9% of population) that are heterozygotes (2pq).
4. Within a population of 2800 cats, the allele frequency of the recessive white allele is 0.4. Calculate the number of cats that are heterozygous in this population.
Answer
q = 0.4 and p = 0.6
5. Sickle-cell anaemia is a condition caused by co-dominant alleles. Individuals with the HbAHbA genotype are free from the condition, but in areas where malaria is prevalent they are more likely to be killed by malaria. Individuals that are homozygous for sickle-cell anaemia HbSHbS have red blood cells that are inefficient at carrying oxygen and, if not treated, sufferers often die in childhood. Individuals who are heterozygous for sickle-cell anaemia HbAHbS have some resistance to malaria, causing them to be at a selective advantage. Out of a population of 6350 people sampled, 1016 were homozygous HbSHbS. Use the Hardy–Weinberg equation to calculate the number of individuals that will be heterozygous.
Answer
q2 = 1016 ÷ 6350 = 0.16, so q = 0.4
p = 0.6, so 2pq = 2 × 0.6 × 0.4 = 0.48
6350 x 0.48 = 3048 heterozygous
6. The Hardy–Weinberg equation is not very useful to predict the prevalence of sickle-cell anaemia in the next generation of a population. Explain why.
Answer
One of the phenotypes (heterozygous) is at a selective advantage.
7. People with sickle-cell anaemia have a different kind of haemoglobin in their red blood cells. The DNA codon GAG that codes for the amino acid glutamic acid is changed to GTG that codes for valine. Name this type of mutation.
Answer
Substitution.
8. Although only one amino acid is different, sickle-cell haemoglobin has very different properties from normal haemoglobin. Use your knowledge of protein structure to explain why.
Answer
Sickle-cell haemoglobin has a different primary structure. This change alters the tertiary structure of the protein, because the folding depends on interactions between amino acids. As a result, different bonds form in different places, such as hydrogen bonds, ionic bonds, and disulphide bridges. These changes in bonding lead to a very different overall shape and properties compared to normal haemoglobin.