G&E: Speciation & Genetic Drift

Question 1

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

Reproductively isolated

Answer 3

Changes in the allele frequency cause changes in phenotype, which means populations of the same species can no longer interbreed to produce fertile offspring.

Question 4

Allopatric speciation

Answer 4

Results from geographical isolation - when a physical barrier divides a population of a species, causing some individuals to become separated from the main population.

Question 5

Sympatric speciation

Answer 5

When speciation occurs due to a population becoming reproductively isolated without any physical separation.

Question 6

What does allopatric speciation require that sympatric speciation doesn’t?

Answer 6

Geographical isolation

Question 7

Explain allopatric speciation:

Answer 7

• Geographically separated populations will experience different conditions and selection pressures.
• Different alleles will be more advantageous in different areas.
• Directional selection will act then act on the alleles.
• Allele frequency will change as mutations occur independently in each population.
• Genetic drift may also affect the allele frequencies.
• Differences accumulate in gene pools of separated populations, causing changes in phenotype frequencies.
• Eventually, populations will have changed so much that they cannot breed to produce fertile offspring.

Question 8

Explain sympatric speciation:

Answer 8

Random mutations could occur within a population, preventing members of that population breeding with other members of the species.

Question 9

Reproductive isolation ocurs because changes in alleles and phenotypes in some individuals prevent them from breeding successfully.

What do these changes include?

Answer 9

• Seasonal - individuals develop different flowering or mating seasons/become sexually active at different times of the year.
• Mechanical - changes in genatalia prevent successful mating.
• Behavioural - group of individuals develop courtship rituals that aren’t attractive to the main population.

Question 10

Genetic drift

Answer 10

Chance, rather than environmental factors, dictates which individuals survive, breed and pass on alleles.

Question 11

Evolution can occur because of what two things?

Question 12

Explain how genetic drift can eventually lead to reproductive isolation and speciation:

Answer 12

• Individuals within populations show variation in genotypes.
• By chance, the allele for one genotype is passed on to the offspring more often than others.
• No. of individuals with the allele increases.
• Changes in allele frequency in two isolated populations could eventually lead to reproductive isolation and speciation.

Question 13

When does evolution by genetic drift have a greater effect?

Answer 13

When population size is small - chance has greater infleunce.

Question 14

Briefly describe how evolutionary change has resulted in diversity of organisms:

Answer 14

• At the start, there was one population of organisms.
• Population was divided and the new population evolved into separate species.
• New species were divided again and new populations evolved into separate species.
• Process has repeated over long periods of time to create millions of new species.