4.4 - Variation and Evolution

Question 1

What is allele frequency?

Answer 1

The number of times an allele appears at a particular locus in a population, expressed as a proportion or a percentage

Question 2

Define allopatric speciation

Answer 2

A form of speciation that occurs when two populations become geographically isolated

Question 3

What is behavioural isolation?

Answer 3

The reproductive isolation of two populations due to differences in their behaviour e.g different mating rituals

Question 4

What is continuous variation?

Answer 4

A type of variation that cannot be categorised e.g skin colour, height. It produces a continuous range in which a characteristic can take any value. Multiple genes influence continuous variation and it is often significantly affected by environmental factors

Question 5

Define discontinuous variation

Answer 5

A type of variation that can be categorised e.g. blood group. A characteristic can only appear in discrete values. One or two genes influence discontinuous variation and environmental factors have little effect

Question 6

Explain what evolution is

Answer 6

The gradual change in the allele frequencies within a population over time. Occurs due to natural selection.

Question 7

Define what the founder effect is

Answer 7

A type of genetic drift in which a few individuals of a species break off from the population and form a new colony. This results in smaller gene pools and an increased frequency of rare alleles.

Question 8

What is a gene pool?

Answer 8

All of the different variations of genes (alleles) in the individuals that make up a population.

Question 9

What is genetic drift?

Answer 9

Variations in allele frequencies in small populations due to chance.

Question 10

What is geographical isolation?

Answer 10

A physical barrier (such as a river or mountains) separates two populations of the same species

Question 11

What is the Hardy-Weinberg principle?

Answer 11

A model that predicts that the ratio of dominant and recessive alleles in a population will remain constant between generations if the following five conditions are met: no new mutations, no natural selection, no migration, large population, random mating. It provides a formula for calculating the frequencies of alleles.

Question 12

Define heritable variation

Answer 12

Genetic differences between individuals

Question 13

Explain what hybrid fertility is

Answer 13

The formation of fertile hybrid offspring (e.g. wheat) due to hybridisation combined with polyploidy which doubles the chromosome number, enabling meiosis.

Question 14

What is hybrid sterility?

Answer 14

The formation of sterile hybrid offspring (e.g. the mule) from the reproduction of individuals of different species; the chromosome sets from each parent differ so are unable to pair up during meiosis.

Question 15

What is interspecific competition?

Answer 15

A type of competition that takes pace between members of different species

Question 16

Define intraspecific competition

Answer 16

A type of competition that takes place between members of the same species

Question 17

What is morphological isolation?

Answer 17

The reproductive isolation of two populations due to the incapability of their reproductive systems.

Question 18

What is natural selection?

Answer 18

The process by which the frequency of beneficial alleles gradually increase in a population’s gene pool over time. This theory was developed by Charles Darwin.

Question 19

What is non-heritable variation?

Answer 19

Acquired differences in the phenotypes of individuals that cannot in inherited.

Question 20

Define what reproductive isolation is

Answer 20

The inability of two populations of the same species to interbreed due to behavioural, morphological or seasonal barriers.

Question 21

What is seasonal isolation?

Answer 21

The reproductive isolation of two populations due to differences in their breeding seasons

Question 22

What are selection pressures?

Answer 22

Environmental factors that drive evolution by natural selection and limit population sizes e.g. competition, predation and disease. They can change the frequency of alleles in a population

Question 23

What is speciation?

Answer 23

A group of similar organisms that are able to breed with one another to produce living, fertile offspring

Question 24

Explain what the student’s t-test is

Answer 24

A statistical test used to determine whether there is a statistically significant difference between the means of two data sets that show normal distribution

Question 25

What is sympatric speciation?

Answer 25

A form of speciation that occurs when two populations within the same area become reproductively isolated

Question 26

What is variation?

Answer 26

The differences between individuals due to genes, the environment or a combination of both