Speciation

Question 1

What genetic factors cause variations in phenotype?

Answer 1

• mutations
• meiosis
• random fertilisation of gametes

Question 2

How do these genetic factors cause genetic variation?

Answer 2

• mutations are the primary source of variation and causes new alleles to arise, increasing the size of the gene pool
• meiosis produces new combinations of alleles through crossing over and independent segregation
• random fertilisation means that gametes fuse randomly, further creating new genetic differences for offspring

Question 3

How do environmental factors cause genetic variation?

Answer 3

• the environment has a large influence on how an organisms genes are expressed and affects the phenotype of an individual
• this includes climate, temperature, PH and food avaliability

Question 4

What three factors cause an organism to be subjected to selection pressures?

Answer 4

• predation
• disease
• competition

Question 5

What do selection pressures determine?

Answer 5

• the frequency of alleles in a gene pool

Question 6

What do selection pressures cause?

Answer 6

• natural selection
• this means that there are differential reproductive successes on allele frequencys

Question 7

Why do organisms over reproduce?

Answer 7

• to ensure a sufficient population survives and can reproduce, producing the next generation
• However, this can cause intraspecific competition to occur as there is a high population for a limited amount of resources
• also in larger populations, there is more genetic variation, increasing the chances of an individual developing a beneficial allele

Question 8

What is the effect of stabilising selection?

Answer 8

• the extremes of a phenotype are eliminated, leaving the average phenotype
• however, when environmental conditions fluctuate, extremes can be favoured

Question 9

What is the effect of directional selection?

Answer 9

• extreme phenotypes are favoured and normal distribution will move in one direction due to fluctuating environmental conditions

Question 10

What is disruptive selection?

Answer 10

• the opposite of stabilising selection
• this occurs when an environmental change exists in two distinct forms, favouring the two extremes

Question 11

Define evolution

Answer 11

the change in allelic frequencies within a population

Question 12

Define speciation

Answer 12

The reproductive isolation leading to the evolution of a new species from existing ones

Question 13

How does speciation occur?

Answer 13

• reproductive seperation
• this occurs when there is a change in alleles and phenotypes of some individuals in a population which prevents successful breeding with other individuals in a population

Question 14

What changes can cause reproductive seperation?

Answer 14

• seasonal changes
• mechanical changes
• behavioural changes

Question 15

What does reproductive isolation mean?

Answer 15

• two populations of a species no longer interbreed and can not produce fertile offspring

Question 16

What are the two types of speciation?

Answer 16

• Allopatric speciation
• Sympatric speciation

Question 17

What occurs during allopatric speciation?

Answer 17

• two populations are geographically seperated due to geographical barriers such as lakes and oceans
• this means they are reproductively seperated and if there are environmental differences, they face different selection pressures
• this means natural selection pressures will occur and each population will evolve differently
• this eventually leads to two different species forming

Question 18

What occurs during sympatric speciation?

Answer 18

• this takes place when there are no geographic barriers and two populations are split due to ecological or behavioural changes

Question 19

Give an example of sympatric speciation

Answer 19

• two populations of fish feed in different places
• one population feeds in open water whereas the other feeds in deep waters
• this ecologically seperates the populations
• there are different selection pressures in the different environments
• for example, longer jaws may be more suitable for deeper waters, this causes natural selection to occur
• this means over time they will continue to diverge until they become different species

Question 20

What is genetic drift?

Answer 20

• when chance affects which individuals in a population survive, breed and pass on their alleles

Question 21

What type of population does genetic drift affect?

Answer 21

• it affects smaller populations

Question 22

Why does genetic drift only affect smaller populations?

Answer 22

• In smaller populations, there is a small gene pool and little genetic variation
• this means that there is not an even chance for alleles to be passed on
• alleles that are passed on affect the whole population, causing genetic drift
• in large populations, genetic drift is limited as alleles are diluted in a large population