Populations and Evolution

Question 1

What is the definition of a population?

Answer 1

Group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed

Question 2

What is the Hardy-Weinberg equation used for?

Answer 2

Estimating frequency of alleles in a population, and to see whether a change in allele frequency is occurring in a population over time

Question 3

What are the 5 assumptions made by the Hardy-Weinburg principle?

Answer 3

• no mutations
• no migration
• no natural selection
• large population
• random mating

Question 4

What are the two formulae in the Hardy-Weinburg principle, and what do the letters represent?

Answer 4

p + q = 1
p^2 + 2pq + q^2 = 1
p - frequency of dominant allele
q - frequency of recessive allele
p^2 - frequency of homozygous dominant
2pq - frequency of heterozygous
q^2 - frequency of homozygous recessive

Question 5

What are the four main reasons for variation in alleles within a species?

Answer 5

• random fertilisation - gametes carrying different alleles randomly join
• independent assortment - maternal and paternal chromosomes randomly line up
• crossing over - chromosomes can cross over, swapping parts of their DNA
• mutation - random change in base sequence of DNA

Question 6

What is intraspecific competition?

Answer 6

• competition within the same species

Question 7

What is the summary of the stages of evolution through natural selection?

Answer 7

1) variety of phenotypes in a population
2) environmental change occurs, so selection pressure changes
3) some organisms have advantageous alleles, which allows the to survive and reproduce
4) advantageous alleles are passed on to their offspring
5) frequency of alleles in a population changes, leading to evolution

Question 8

What is selection?

Answer 8

Process by which individuals that are better adapted to their environment are more likely to survive and breed, so can pass on advantageous alleles

Question 9

What are the three key types of selection?

Answer 9

• directional - occurs when environmental conditions change, so organisms with the phenotypes better suited to new condition are more likely to survive, results in the mean of the population moving in that direction
• stabilising - stable environmental conditions so those with greater genetic diversity are selected against
• disruptive - both extreme phenotypes are favoured, often due to a significant change, resulting in the mean of the population moving away from the centre

Question 10

What is a gene pool?

Answer 10

Sum of all the alleles of the genes of a population at a particular time

Question 11

What is allele frequency?

Answer 11

How frequently different alleles occur with the gene pool

Question 12

What is genetic drift?

Answer 12

Random changes in allele frequencies within a populations gene pool due to chance events
- mainly effects small populations

Question 13

What is reproductive isolation, and what can it lead to?

Answer 13

• when populations cannot interbreed successfully to produce fertile offspring
• leads to genetic isolation, and prevents the exchange of genes between the populations, potentially causing speciation

Question 14

What are the stages allopatric speciation?

Answer 14

1) some members of a population are geographically separate from the rest by a physical barrier
2) geographical separation exposes distinct parts of the population to different environmental pressures
3) leads to reproductive isolation
4) prevents gene flow, and genetic divergence occurs due to differing selection pressures
5) populations will evolve separately, and speciation will occur

Question 15

What are the two types of speciation?

Answer 15

Allopatric and Sympatric

Question 16

What is sympatric speciation?

Answer 16

• speciation takes place within same geographical location
• ecological or behavioural separation mechanisms like habitat preferences, mate selection or chromosomal changes lead to a group becoming reproductively isolated
• causes populations to evolve separately and form separate species

Question 17

What is evolution?

Answer 17

Change in allele frequencies in a population