BIology Evolution 6.2

Question 1

Natural selection

Answer 1

• Individuals vary due to different alleles from mutations
• Selective pressures act on the population
• Individuals with a certain allele are more likely to survive and reproduce
• A greater proportion of the next generation inherit the advantageous gene
• Over time, the allele frequency increases

Question 2

What is selection likely to be if the environment isn’t changing very much?

Answer 2

Stabilising selection

Question 3

What is the selection likely to be if the environment is changing?

Answer 3

Directional selection

Question 4

What is genetic drift?

Answer 4

When chance dictates which alleles are passed on

It can be due to geographical isolation or reproductive isolation or a catastrophic event

Question 5

What is a genetic bottleneck?

Answer 5

When the population shrinks and then increases again, changing the allele frequency and genetic diversity and reduces the gene pool

Question 6

What is the founder effect?

Answer 6

When a new smaller population is founded from a larger population, with a small amount of different alleles, there is a loss of genetic variation

Question 7

What is the Hardy-Weinberg principal?

Answer 7

It states that the genetic variation in a population will stay constant between generations if there are no disruptive factors because it is in equilibrium

Question 8

What are the assumptions of the Hardy-Weinberg principal?

Answer 8

Large population
No natural selection
Random mating
No immigration/emigration
No mutation

Question 9

How do you work out the frequency of alleles using the Hardy-Weinberg principal?

Answer 9

p + q = 1
p = freq of dominant allele
q = freq of recessive allele

Question 10

How do you work out the frequency of genotypes using the Hardy-Weinberg principal?

Answer 10

p^2 + pq + q^2 = 1
p^2 = freq of homozygous dominant
pq = freq of heterozygous
q^2 = freq of homozygous recessive

Question 11

What is speciation?

Answer 11

The development of a new species

Question 12

What is allopatric speciation?

Answer 12

When geographical isolation leads to natural selection and creates a new species that are reproductively isolated

Question 13

What can cause reproductive isolation?

Answer 13

Seasonal changes - different mating seasons
Mechanical changes - changes in genitalia
Behavioural changes - different courtship rituals

Question 14

What is sympatric speciation?

Answer 14

Speciation without geographical isolation

eg. by a mutation