1. What is meant by the term "population" ?
Answer
A group of organisms of the same species that are in a particular space and a particular time, with the ability to interbreed.
2. If a population has a high frequency of different alleles, what might be said about their gene pool ?
Answer
They are said to have a large and varied gene pool.
3. In the Hardy–Weinberg equation, what does each part of the equation p2 + 2pq + q2 = 1 represent ?
Answer
p2 = individuals that are homozygous dominant
2pq = individuals that are heterozygous
q2 = individuals that are homozygous recessive
4. Beak colour in finches is determined by two alleles, black (D) and yellow (d). There are 210 individuals that are homozygous dominant, 245 that are heterozygous and 45 that are homozygous recessive. Calculate the frequency of each allele.
Answer
There are 210 + 245 + 45 = 500 individuals in total, and since each individual carries two alleles, the population has
The number of dominant alleles (D) present in the population is
Therefore, the frequency of allele D is
Since the total allele frequency must equal 1, the frequency of allele d is
5. One gene for fur colour in cats has three alleles. B (black) is dominant over b (chocolate) but a third allele, b' (cinnamon) is recessive to both the chocolate and black alleles. Give the possible genotype(s) of a black cat, a chocolate cat and a cinnamon cat.
Answer
black: BB, Bb, Bb';
6. A different sex-linked gene in cats has two codominant alleles. XO codes for orange fur and XB for non-orange fur. A cat with the genotype XOXB is tortoiseshell. Male tortoiseshell cats are very rare and usually have chromosome abnormalities. Explain why.
Answer
Males have only one X chromosome (so can only have one allele of this gene). Tortoiseshell male would have two X chromosomes and be XXY.
7. Use a genetic diagram to show the possible genotypes and phenotypes of the offspring of a tortoiseshell female and an orange male.
Answer
Parents: XOXB × XOY
Gametes: XO XB XO Y
Offsprings: 1 orange female : 1 tortoiseshell female : 1 orange male : 1 non-orange male