population and evolution 3.7

Question 1

define species

Answer 1

a group of organisms that can interbreed to produce fertile offspring

Question 2

define population

Answer 2

all of the organisms of a particular species that live in the same place

Question 3

define gene pool

Answer 3

the range of different alleles
existing for a particular locus
within a population

Question 4

define allele frequency

Answer 4

the proportion of a certain allele
within a gene pool

Question 5

what is the hardy-weinberg principle

Answer 5

allows us to estimate the frequency of alleles in a population
as well as if allele frequency is changing over time

Question 6

assumptions made by hardy-weinberg principle (5)

Answer 6

no mutations to create new alleles
no migration in or out of population
no selection, alleles are equally passed on
random fertilisation
large population

Question 7

hardy-weinberg equation for calculating allele frequency

Answer 7

p + q = 1

p = frequency of dominant allele
q = frequency of recessive allele

Question 8

hardy-weinberg equation for calculating genotype frequency

Answer 8

p2 + 2pq + q2 = 1

p2 = frequency of homozygous dominant
2pq = frequency of heterozygous
q2 = frequency of homozygous recessive

Question 9

factors that cause phenotypic variation within a species (4)

Answer 9

mutation of alleles
random fertilisation of gametes
random assortment of genetic material during meiosis
environmental influences

Question 10

why does natural selection occur (3)

Answer 10

predation
disease
competition

Question 11

how does natural selection cause a change in a population’s gene pool over generations

Answer 11

organisms with advantageous characteristics more likely to survive
and pass on their favourable alleles to offspring
frequency of unfavourable allele decreases
frequency of favourable allele increases

Question 12

define stabilising selection

Answer 12

occurs when environmental conditions stay the same
individuals closest to mean are favoured
new characteristics are selected against
results in low diversity

Question 13

define directional selection

Answer 13

occurs when environmental conditions change
individuals with phenotypes suited to the new conditions will survive and pass on their genes
over time the mean of the population will move towards these characteristics

Question 14

define disruptive selection

Answer 14

both extremes of the normal distribution are favoured over the mean
over time the population becomes phenotypically divided

Question 15

define speciation

Answer 15

where a population is split and isolated
there are different selective pressures on the two groups
if genetic makeup changes to the extent that the two groups can no longer interbreed
they have become separate species

Question 16

define allopatric speciation

Answer 16

speciation resulting from a physical barrier
the environments occupied by the two groups are different
therefore different alleles are favoured

Question 17

define sympatric speciation

Answer 17

speciation resulting from a non-physical barrier
eg a mutation that no longer allows two organisms to produce fertile offspring
any changes in anatomy or behaviour may also prevent breeding

Question 18

define genetic drift

Answer 18

a change in a populations allele frequencies
that occurs due to chance rather than selective pressures

Question 19

why does genetic drift affect small populations more than large ones

Answer 19

gene pool is smaller
less alleles available
any change in allele frequency becomes pronounced very quickly