18. POPULATIONS & EVOLUTION

Question 1

Define population

Answer 1

All the individuals of one species in one area at a time

Question 2

Define gene pool

Answer 2

All the alleles of the genes within a population at one time

Question 3

Define allele frequency

Answer 3

The proportion of an allele within the gene pool

Question 4

What does the Hardy Weinberg principle predict?

Answer 4

That the frequency of alleles in a population will not change over time

Question 5

Describe the five assumptions the Hardy Weinberg principle makes

Answer 5

There is no migration to introduce or remove alleles from the population
There are no mutations to create new alleles
There is no selection favouring particular alleles
Mating is random
The population is large

Question 6

Recall both Hardy Weinberg equations

Answer 6

p + q = 1
p2 + 2pq + q2 = 1

Question 7

What is p in the Hardy Weinberg equation?

Answer 7

Number of dominant alleles in the population

Question 8

What does p2 stand for in the Hardy Weinberg equation?

Answer 8

Number of homozygous dominant genotypes in the population

Question 9

What is q in the Hardy Weinberg equation?

Answer 9

Number of recessive alleles in the population

Question 10

What does q2 stand for in the Hardy Weinberg equation?

Answer 10

Number of homozygous recessive genotypes in the population

Question 11

What does 2pq stand for in the Hardy Weinberg equation?

Answer 11

Number of heterozygous genotypes in the population

Question 12

How do most new alleles arise?

Answer 12

Mutations

Question 13

What two factors cause phenotypic variation in a population?

Answer 13

Mutations (creating genetic variation), and environmental factors

Question 14

Define what a selective pressure is

Answer 14

Any reason for individuals to have a survival advantage

Question 15

Give examples of selective pressures

Answer 15

Competition for food, space, water, mates and territory. Diseases.

Question 16

Natural selection will only occur if which two pre-requisites occur together

Answer 16

Phenotypic variation and a selection pressure

Question 17

In natural selection, which individuals are more likely to reproduce more?

Answer 17

The individuals with the selective advantage

Question 18

In natural selection, which alleles are more likely to be passed onto offspring?

Answer 18

The alleles that code for the phenotype with the selective advantage

Question 19

What happens to the frequency of alleles in subsequent generations because of natural selection?

Answer 19

The alleles coding for the phenotype with the selective advantage will increase in frequency

Question 20

Name the three types of natural selection

Answer 20

Directional, stabilising and disruptive

Question 21

In directional selection, what happens to the frequency of alleles in subsequent generations?

Answer 21

Directional selection will increase the frequency of alleles in one direction

Question 22

When will directional selection occur?

Answer 22

When there is a change in the environment

Question 23

Why does directional selection occur?

Answer 23

Because one phenotypic extreme is better adapted / has a selective advantage

Question 24

What happens to the modal phenotype in directional selection?

Answer 24

It changes in one direction

Question 25

Give one example of directional selection

Answer 25

Antibiotic resistance

Question 26

When will stabilising selection occur?

Answer 26

When the environment doesn’t change

Question 27

Why does stabilising selection occur?

Answer 27

Because the modal phenotype has the selective advantage

Question 28

What happens to the standard deviation around the modal phenotyoe in stabilising selection?

Answer 28

It decreases over time

Question 29

Give one example of stabilising selection

Answer 29

Birth weights

Question 30

When will disruptive selection occur?

Answer 30

(Often) when an environmental factors takes two extreme forms

Question 31

Why does disruptive selection occur?

Answer 31

It occurs because extreme phenotypes have the selective advantage

Question 32

What happens to the modal phenotype in disruptive selection?

Answer 32

Initially the modal phenotype will decrease over time, and two new modes will develop at the extremes

Question 33

Give one example of disruptive selection

Answer 33

Size of male salmon

Question 34

Define speciation

Answer 34

Whe two populations of the same species become genetically different enough that they can no longer interbreed to produce fertile offspring

Question 35

Define reproductive isolation

Answer 35

The inability of two populations to breed due to geographical, behavioural, physiological or genetic barriers.

Question 36

Which type of speciation occurs when reproductive isolation occurs because of geographical isolation?

Answer 36

Allopatric speciation

Question 37

Describe how allopatric speciation occurs due to geographical isolation

Answer 37

Reproductive isolation means both populations accumulate different beneficial genetic changes over time, which leads to changes in allele frequencies in each population.
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Question 38

At which point does allopatric speciation occur?

Answer 38

When indviduals in the population can no longer interbreed to produce fertile offspring

Question 39

Which type of speciation occurs when reproductive isolation occurs because of behavioural differences?

Answer 39

Sympatric speciation

Question 40

Give examples of how behavioural differences can cause reproductive isolation

Answer 40

Different courtship rituals
Being fertile at different times of the year
Different feeding times or foods

Question 41

Which type of selection can lead to sympatric speciation?

Answer 41

Disruptive selection

Question 42

Describe how sympatric speciation occurs due to behavioural differences

Answer 42

This occurs in the same habitat. Reproductive isolation means both populations accumulate different beneficial genetic changes over time, which leads to changes in allele frequencies in each population.
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Question 43

At which point does sympatric speciation occur?

Answer 43

When indviduals in the population can no longer interbreed to produce fertile offspring