Speciation and genetic drift

Question 1

What is speciation?

Answer 1

The development of a new species from an existing species

Question 2

When does speciation occur?

Answer 2

When populations of the same species become reproductively isolated

Question 3

What does reproductively isolated mean?

Answer 3

Changes in allele frequency causes changes in phenotype which means they can no longer interbreed to produce fertile offspring

Question 4

When can reproductive isolation occur?

Answer 4

Physical barriers which cause geographical isolation

Without physical barriers

Question 5

What are the two types of speciation?

Answer 5

Allopatric

Sympatric

Question 6

What is allopatric speciation?

Answer 6

Populations that are geographically isolated and will experiences slightly different conditions

Question 7

When two populations become geographically isolated, how does this change allele frequencies?

Answer 7

• Different alleles will be more advantageous in different populations so natural selection occurs
• Allele frequencies will also change as mutations occur independently in each population
• Genetic drift may also affect the allele frequencies in one or both populations

Question 8

How do changes in allele frequency cause allopatric speciation?

Answer 8

The changes in allele frequency will lead to differences accumulating in the gene pools of the separated populations, causing changes in phenotype frequencies
Over time, individuals from different populations will have changed so much that they wont be able to breed with one another to produce fertile offspring and they have become reproductively isolated.

Question 9

What is sympatric speciation?

Answer 9

Occurs when random mutations within a population prevents individuals that carry the mutation from breeding with other members of the population that don’t carry the mutation

Question 10

What does sympatric speciation not include?

Answer 10

Geographical isolation

Question 11

Which type of speciation is rare?

Answer 11

Sympatric

Question 12

What is an example of sympatric speciation?

Answer 12

Sometimes a mutation can occur in individuals, known as polyploidy, causing them to have more chromosomes than the diploid population. This means they cant reproduce sexually to give fertile offspring

Question 13

What are the mechanisms of reproductive isolation?

Answer 13

• Seasonal changes
• Mechanical changes
• Behavioural changes

Question 14

What are seasonal changes?

Answer 14

Individuals develop different flowering or mating seasons or become sexually active at different times of the year. They cant breed as they aren’t reproductively active at the same time

Question 15

What are mechanical changes?

Answer 15

Changes in the shape, size or function of the genitalia can prevent successful mating

Question 16

What are behavioural changes?

Answer 16

Courtship behaviour may change and therefore they wont be seen as attractive anymore, prevents breeding even if they could do it successfully

Question 17

What is the effect of selection pressures?

Answer 17

They can change the allele frequency of a population over time

Question 18

What two ways can evolution occur?

Answer 18

Natural selection

Genetic drift

Question 19

What is genetic drift?

Answer 19

Instead of environmental factors affecting which individuals survive, breed and pass on their alleles, chance dictates which alleles are passed on

Question 20

How does genetic drift work?

Answer 20

1) Individuals within a population show variation in their genotypes
2) By chance, the allele for one genotype is passed on to more offspring than the others so the number of individuals with the allele increases
3) If by chance the same allele is passed on more often again and again, it can lead to evolution as the allele becomes more common in the population

Question 21

What might happen if enough differences in allele frequencies build up due to genetic drift?

Answer 21

Leads to reproductive isolation and speciation

Question 22

Out of evolution and genetic drift, which has a greater effect in smaller populations?

Answer 22

Genetic drift