Section 7 - Populations and evolution

Question 1

What does gene pool mean?

Answer 1

All of the alleles of all of the genes present in a population

Question 2

What is allele frequency?

Answer 2

The number of times an allele appears within the gene pool

Has a value between 0 and 1

Question 3

What is the Hardy Weinberg principle used to calculate?

Answer 3

Used to calculate the frequencies of the different alleles of a gene in a population

Question 4

What assumptions are made in the Hardy Weinberg principle?

Answer 4

No mutations- no new alleles

No migration- no new alleles introduced/ lost

No selection- no alleles are favoured/ eliminated

Mating is random- alleles mixed randomly

Population is large- no genetic bottlenecks

Question 5

What is the equation for working out alleles?

Answer 5

Only 2 alleles so: P + Q = 1

Probability of dominant allele = P
Probability of recessive allele = Q

Question 6

What is the equation for working out genotype?

Answer 6

P^2 + 2PQ + Q^2 = 1

Dominant homozygous = P^2
Recessive homozygous = Q^2
Heterozygous = 2PQ

Question 7

When is P^2 + 2PQ + Q^2 = 1 used?

Answer 7

When given information about phenotypes/ genotypes

Question 8

When is P + Q = 1 used?

Answer 8

When given information about allele frequency

Question 9

What does the Hardy Weinberg principle assume about allele frequency?

Answer 9

Assumes that frequencies of the alleles in a population remain constant between generations

Question 10

What is variation?

Answer 10

The differences that exist between individual organisms

Question 11

What is interspecific variation?

Answer 11

Variation between species

Question 12

What is intraspecific variation?

Answer 12

Variation between members of the same species

Question 13

What is continuous variation and how would it be displayed?

Answer 13

Consists of a range of values between 2 extremes

Most close to mean values

Usually polygenic and affected by the environment

Use tally chart and plot results in a histogram

Question 14

What is discontinuous variation and how would it be displayed?

Answer 14

2 or more distinct categories with no intermediate values

Monogenic

Environment has little / no effect (blood groups)

*Using bar chart

Question 15

What is variation through natural selection?

Answer 15

Mutations produce variation

Some individuals are more likely to survive

They reproduce and pass on favourable alleles to offspring = DIFFERENTIAL REPRODUCTIVE SUCCESS

Advantageous alleles become more frequent in population

Population evolves

Question 16

What is differential reproductive success?

Answer 16

When individuals reproduce, they pass on favourable alleles to offspring

Question 17

What are selection pressures?

Answer 17

Environmental factors that confer an advantage to some members of a population over others

(Predation, disease, competition)

Question 18

What are the 3 types of natural selection?

Answer 18

1. Directional
2. Stabilising
3. Disruptive

Question 19

What is directional selection?

Answer 19

Acts against one extreme in a range of phenotypes

One phenotype becomes rare and alternative phenotype becomes more common

Question 20

What is stabilising selection?

Answer 20

Acts against both extremes in a range of phenotypes

Question 21

What is disruptive selection?

Answer 21

Selection that removes individuals from centre of phenotypic disruption

Causes distribution to become bimodal

2 extremes become more common and intermediate states will be lost

Leads to 2 new species

Question 22

What is speciation?

Answer 22

The development of a new species from an existing one

Question 23

What is speciation caused by?

Answer 23

By reproductive isolation

Change in allele frequency which means they can no longer breed to produce fertile offspring

Question 24

Why does speciation occur?

Answer 24

Due to geographical barriers (allopatric speciation) or without a barrier (sympatric speciation)

Question 25

What is allopatric speciation?

Answer 25

Speciation due to geographical barrier

Question 26

What is sympatric speciation?

Answer 26

Speciation occurring without a barrier

Question 27

What 3 reasons does reproductive isolation occur for?

Answer 27

Timing - individuals develop different mating times

Physical changes- change in structure of gametes

Behavioural changes- courtship rituals (bird songs)

Question 28

What is genetic drift?

Answer 28

Change determines if alleles are passed on

Question 29

What is evolution by natural selection?

Answer 29

When selection pressures change allele frequencies over time

Question 30

What does genetic drift do?

Answer 30

One genotype happens to get passed on to more offspring

Evolution occurs as allele becomes more common

Biggest effect in a small population

Question 31

What is a recessive allele?

Answer 31

Only expressed in phenotype when 2 alleles are present

Question 32

What is genetic drift?

Answer 32

Process whereby an allele becomes more common, by chance, in a population

Question 33

What is a population bottleneck?

Answer 33

A sharp reduction in the size of a population due to environmental events

Question 34

What is the founder effect?

Answer 34

Loss of genetic variation that occurs when a new population is established by a very small number of individuals

Question 35

What does the Hardy-Weinberg principle predict? [3]

Answer 35

Frequency of alleles

Will stay constant from one generation to the next

Providing no mutation

Question 36

What are the consequences of widely separated species?

Answer 36

Genetically isolated populations

Allopatric speciation

Genetic drift

Loss of alleles