L1 - Gene Pools (& selection)

Question 1

Define Population

Answer 1

A group of organisms of the same species living in a particular area at a particular time - they have the potential to interbreed

Question 2

Define Allele frequency

Answer 2

How often an allele occurs in a population

Question 3

Define Gene pool

Answer 3

The complete range of alleles present in a population

Question 4

Why can some genotypes not be measured by looking at the phenotypes?

Answer 4

If a trait is recessive e.g. blue eyes, if the organism has this trait then they would be homozygous recessive. However, if they did not, you don’t know if they’re heterozygous, or homozygous dominant

Question 5

State the 7 conditions required for Hardy-Weinburg equilibrium

Answer 5

1) No mutations
2) No natural selection
3) Very large population
4) All members of the population breed
5) Random mating
6) All parents produce the same number of offspring
7) No migration in or out

Question 6

State the Hardy-Weinburg equilibrium equation for genotypes

Answer 6

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

Question 7

State the Hardy-Weinburg equilibrium equation for alleles

Answer 7

p + q = 1
p = Frequency of the dominant allele
q = Frequency of the recessive allele

Question 8

Define variation

Answer 8

The difference in characteristics shown by organisms belonging to the same natural population or species

Question 9

State the two types of variation

Answer 9

Continous and discontinuous

Question 10

In discontinuous variation, the phenotypes…

4 points

Answer 10

1) Have distinct categories
2) Normally qualitative, with no overlap between categories
3) Are controlled by a small number of alleles
4) Are affected by the environment very little

(The opposite to continuous variation!)

Question 11

Give 3 examples of discontinuous variation

Answer 11

a) ABO blood groups
b) Tounge rolling
c) MN blood groups

Question 12

In continuous variation, the phenotypes…

4 points

Answer 12

1) Have no distinct categories
2) Normally quantitative, with overlaps between categories
3) Controlled by a large number of alleles (polygenic inheritance)
4) Are influenced largely by the environment

(The opposite to discontinuous variation!)

Question 13

Which HAS gaps between categories, bar chart or histogram?

Answer 13

Bar chart

Question 14

Which has NO gaps between categories, bar chart or histogram?

Answer 14

Histogram

Question 15

Define stabilising selection, draw the graph and give an example

Answer 15

Stabilising selection = Where individuals with alleles for characteristics towards the mean are more likely to survive and reproduce. It occurs when the environment isn’t changing and it reduces the range of possible phenotypes

Example = Human birth weights

Question 16

Define directional selection, draw the graph and give an example

Answer 16

Directional selection = Where individuals with alleles for a single extreme phenotype are more likely to survive and reproduce. This could be in response to an environmental change

Example = Antibiotic resistance in bacteria

Question 17

Define disruptive selection, draw the graph and give an example

Answer 17

Disruptive selection = Where individuals with alleles for both extreme phenotypes (at either end of the range) are more likely to survive and reproduce. Occurs when the environment favours more than one phenotype

The opposite to stabilising selection, as characteristics towards to middle of the range are lost.

Example = Beak size in birds

Question 18

Define Selection pressure

Answer 18

Any factor that affects an organism’s chance of survival and reproduction

Question 19

Define Evolution

Answer 19

A change in allele frequencies over time

Question 20

Define Speciation

Answer 20

The evolution of a new from an existing species

Question 21

Define Allopatric speciation

Answer 21

The development of a new species via geographical isolation, which causes reproductive isolation.

Question 22

Allopatric & Sympatric
Allopathic & Sympathic

Which is the correct spelling?

Answer 22

Allopatric & Sympatric = Correct

AllopatRIC & SympatRIC

Question 23

Define Sympatric speciation

Answer 23

The development of a new species via random mutations, which cause reproductive isolation e.g. polyploidy

Question 24

State three selection pressures

Answer 24

Predation, disease and competition

Question 25

Describe three types of changes that can lead to reproductive isolation in a species

Answer 25

1) Seasonal - individuals from the same population develop different flowering or mating seasons or become sexually active at different times of the year
2) Mechanical - changes in genitalia prevent successful mating
3) Behavioural - a group of individuals develop courtship rituals that aren’t attractive to the main population

Question 26

Define Genetic drift

Answer 26

When chance, rather than environmental factors, dictates which individuals survive, breed and pass on their alleles

Question 27

How is genetic drift different to natural selection?

Answer 27

Natural selection:

a) Large population sizes
b) Occurs when different selection pressures can change the allele frequencies in two geographically isolated species

Genetic drift

a) Small population sizes
b) Occurs via random mutations

Question 28

Why is genetic drift important only in small populations?

Answer 28

Chance has a greater influence on smaller populations. In larger populations, any chance variations in allele frequency tend to even out across the whole population

Question 29

What is a genetic bottleneck?

Answer 29

When a population’s size is reduced dramatically for at least one generation

Question 30

What is the Founder effect?

Answer 30

When a new colony is started by a few members of the original population

Question 31

The small population size in the Founder effect means the colony may have:

Answer 31

a) Reduced genetic variation

b) Non-random sample of genes from the original population

Question 32

Give an example of the Founder effect

Answer 32

The Amish population in America