Evolution Module 6

Question 1

The complete range of alleles present in a population is known as the?

Answer 1

Gene pool

Question 2

How are new alleles generated?

Answer 2

Mutations

Question 3

Definition of evolution?

Answer 3

Change in allele frequency

Question 4

Describe how evolution occurs via natural selection?

Answer 4

Individuals within a population vary because they have different alleles

Predation, disease and competeition (all selection pressures) create a struggle for survival

Because individuals vary some are better adapted for to the selection pressures than others

individuals with an allele that increases their chance of survival are more likely to survive, reproduce and pass on the advantageous allele than individuals with different allels

This means a greater proportion of the next generation inherit the advantageous allele

They in turn are more likely to reproduce and pass on their genes, so the frequency of the advantageous allele passes on from generation to generation

This is natural selection

Question 5

What’s stabilising selection?

Answer 5

When the environment isn’t changing much, individuals with alleles towards the middle of the range are more likely to survive and reproduce - so the amount of phenotypes is reduced

Question 6

What’s directional selection?

Answer 6

When there’s a change in the environment, and the individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce

Question 7

Describe how evolution occurs via genetic drift?

Answer 7

Individuals within a population show variation in their genotypes

By chance the allele for one genotype is passed on to the offspring more often than others

So the number of individuals with the allele increases

If by chance the same allele is passed on more often again, again and again it leads to evolution as it becomes more common in the population

Question 8

When is genetic drift most effective and 2 examples when it is?

Answer 8

In small populations where chance has a greater influence

For example in a genetic bottleneck such as a massive natural disaster and the population is massively reduced

Or the founder effect, where a few organisms start a new population and there are only small amount of different alleles in the initial gene pool

Question 9

What needs to be true for the principle that allele frequencies won’t change from one generation to next?

Answer 9

Large population

No immigration or emigration, mutations or natural selection

Question 10

Equation to predict allele frequency?

Answer 10

p + q = 1

p = the frequency of the dominant allele
q = the frequency of the recessive allele

May have to combine with other equation in a question

Question 11

Equation to predict genotype frequency?

Answer 11

p^2 + 2pq + q^2 = 1

p^2 = the frequency of homozygous dominant genotype
2pq = the frequency of the heterozygous genotype
q^2 = the frequency of the homozygous recessive genotype

May have to combine with the other equation in a question

Question 12

What is artificial selection?

Answer 12

When humans select individuals in a population to breed with each other to get desirable traits

Question 13

Negatives of artificial selection?

Answer 13

Reduces the number of alleles in the gene pool
Potentially useful alleles are lost
Very vulnerable to disease

Can exaggerate certain traits leading to health problems

Increased incidence of genetic disease

Question 14

Definition of a species?

Answer 14

A group of similar organisms that can reproduce to giver fertile offspring

Question 15

What’s speciation?

Answer 15

The development of a new species, occurs when populations of the same species become reproductively isolated - can longer breed together to produce fertile offspring

Question 16

Describe how geographical isolation and natural selection lead to allopatric isolation?

Answer 16

Geographical isolation occurs when a physical barrier divides a population of a species, eg a volcano eruption

Conditions on either side will be slightly different

Because the environment is different on either side different characteristics will become more common due to natural selection

So this will change allele frequency aswell as mutations,

Eventually they will have changed so much so can’t reproduce with each to produce fertile offspring, so are now categorised as different species

Question 17

3 ways reproductive isolation can occur?

Answer 17

Seasonal changes - they have different mating seasons

Mechanical changes - gentitalia

Behavioural changes

Question 18

What’s sympatric speciation?

Answer 18

Specaition without geographical isolation