1. Explain what is meant by the term "differential reproductive success".
Answer
When organisms with one phenotype are more likely to survive, reproduce and pass on their alleles than an organism with a different phenotype.
2. In order for two new species to arise from one original population, what is the final stage that must occur in order to ensure that they diverge into two separate species ?
Answer
Must be reproductively separated.
3. Apple maggot flies feed and mate on apple trees in North America. Their original host plant was the hawthorn tree. When apple trees were introduced to North America, some flies in the population started to populate apple trees. Scientists noted that flies that hatched on a specific tree, hawthorn or apple, then tended to feed and mate on that tree for the remainder of their life. Scientists think that the apple maggot flies in North America might evolve into two separate species. Explain how.
Answer
If they are mating and feeding on different trees they will be reproductively isolated. Mutation will occur, where advantageous characteristics will reproduce and pass on their alleles more. Allopatric speciation will occur. Different selection pressures will be present, meaning over time different phenotypes will be selected for and against.
4. How might scientists determine whether the flies from apple trees are a different species from the flies on hawthorn trees ?
Answer
Breed the two flies together, and then breed their offspring. If offspring are fertile, then they are still the same species.
5. There are about 100000 individuals who have all descended from about 200 ancestors centuries ago. This population has an unusually high incidence of Ellis–van Creveld syndrome, which is an example of genetic drift. Explain why genetic drift is more important in small populations.
Answer
Each individual in a small population represents a larger proportion of the entire population compared to an individual in a large population. Due to the role of chance, when a small sample is separated from a larger population, the proportion of alleles may differ greatly between samples.
6. Ellis–van Creveld syndrome is caused by a recessive allele. This population is isolated and they usually marry within their population. Explain how this increases the incidence of Ellis–van Creveld syndrome.
Answer
More people in this population likely to carry one copy of recessive allele. When individuals marry, likely that partner has the same recessive alleles.
7. Nephropathic cystinosis is a genetic condition caused by an autosomal recessive allele. One child in 44 in this population is born with nephropathic cystinosis. Use the Hardy–Weinberg equation to calculate the percentage of the population who are heterozygous for this condition.
Answer
q2 = 1/44 = 0.0227 ➞ q = 0.151
p = 1 – 0.151 = 0.849
2pq = 2 × 0.849 × 0.151 = 0.256
25.6% of population are heterozygous