selection

Question 1

what is a gene pool
what is allele frequency

Answer 1

gene pool- all the alleles of all the genes in a population

allele frequency= relative number of alleles of a particular gene in a population

Question 2

what factors influence population size

Answer 2

-selection pressures such as food, predators, prey, disease, shelter

Question 3

what shape graph does continuous variation produce

Answer 3

normal distribution or bell-shaped curve

Question 4

what are 3 types of selection pressure that affect continuous variation e.g height, weight

Answer 4

-stabalising
-directional
-disruptive

Question 5

explain stabalising selection and the graph

Answer 5

-selection favours the mean of the distribution
-occurs environment remains constant
-reduction in genetic diversity
-increases allele frequency for the average phenotype
-narrows the curve
-e.g human birth weights

Question 6

explain directional selection

Answer 6

-favours one extreme
-occurs when the environment changes
-results in a shift in the mean so shifts curve in the direction of the favoured extreme
-increase in allele frequency for one extreme phenotype
-e.g antibiotic resistance

Question 7

explain disruptive selection

Answer 7

-favours both extreme phenotypes over the intermediate
-if the environment changes, selection pressure changes e.g rabbits moving to a rocky area where white and black provide better camouflage than agouti
-frequency of white and black fur alleles would increase as would frequency of individuals with white and black fur in the population

Question 8

what is genetic drift

Answer 8

variation in the frequency of different alleles in a small population as a result of the chance disappearance of particular alleles
-alleles are lost randomly not as a result of selection pressure
-drift in allele frequency will be greater the smaller the population

Question 9

what can genetic drift result in

Answer 9

-genetic bottleneck
-founder effect

Question 10

explain genetic bottleneck effect

Answer 10

-crash in population size due to catastrophe followed by recovery
-the small population of surviving individuals have a random set of alleles that show less genetic variation than those in the original population

Question 11

explain the founder effect

Answer 11

a new population established from a large parent population, as the new population is small some alleles will be randomly under- represented or missing
-population that is genetically distinct from the original will arise