Gene pools and selectionEdexcel A-Level Biology B: Mind map

Exam questions on Gene pools and selection

1. In humans, babies with a very low or a very high birth mass have a higher death rate than babies with a birth mass close to the average, which is about 3.3 kg. The alleles that influence birth mass have remained at similar frequencies in the population over many generations.
   Explain how selection keeps the allele frequencies for birth mass similar from one generation to the next.2 marks
2. On an island, a population of finches feeds on seeds. Small soft seeds and large hard seeds are both plentiful, but seeds of medium size are scarce. Birds with small beaks are efficient at eating small seeds and birds with large beaks are efficient at cracking large seeds. Birds with medium-sized beaks cannot feed efficiently on either.
   Explain how disruptive selection changes the frequencies of the alleles for beak depth in the finch population.2 marks
3. Northern elephant seals were hunted to about 20 individuals in the 1890s. Their numbers have since recovered to over 100 000, but genetic analysis shows that they have much less genetic variation than southern elephant seals, which were not hunted so severely. A small group of northern elephant seals later colonised a new island.
   Explain how the hunting of the northern elephant seals reduced their genetic variation.3 marks