AQA A-Level Biology Paper 2 2024/2025
1. Alleles that are neither dominant nor recessive to Codominant
one another, so both alleles are always expressed
in the phenotype.
2. The inheritance of a single gene Monohybrid inheri-
tance
3. Physical, behavioural, biochemical expression of Phenotype
an organisms genotype
4. The type of genes an individual has Genotype
5. Alles that is always expressed in the phenotype Dominant
6. Only expressed in the phenotype when homozy- Recessive
gous
7. both alleles are the same Homozygous
8. Both alleles for a specific gene are different Heterozygous
9. Position of a gene on a chromosome Loci
10. A set of instructions for a specific polypeptide Gene
11. Different forms of a gene Allele
12. 1. Expected ratios are probability Suggest four reasons
2. Sexual reproduction is random due to random why observed ratios
fusion of gametes and random assortment homol- are not the same as
ogous chromosomes. expected ratios (4).
3. Small sample size
4. Linked genes
13. 1. Homologous chromosomes pair up Meiosis results in
2. Crossing over / chiasmata form; cells that have the
3. Produces new combination of alleles haploid number of
4. Chromosomes separate at random chromosomes and
5. This produces varying combinations of genes show genetic varia-
6. Chromatids separated at meiosis II tion. Explain how. (6)
, AQA A-Level Biology Paper 2 2024/2025
14. 1. Refer to the specific individuals (using their Pedigree Questions
number) Mark Scheme (3)
2. Explain what happened with the genes (passed
on recessive/dominant)
3. Describe the genotype of your examples and
mention their phenotype (homozygous/heterozy-
gous etc)
15. Group of organisms of the same species occupy- Populations
ing a particular space at a particular time that can
potentially interbreed to produce fertile offspring.
16. The total number of genes of every individual in an Gene pool
interbreeding population.
17. How often an allele appears in a population. Allele frequency [def-
inition][Equation] (2)
desired allele/total alleles = allele frequency (deci-
mal form)
18. No emigration or immigration Hardy-Weingberg
No mutations Assumptions (4)
Mating is random
No natural selection
19. 1. Selection pressure exists in an environment Natural selection MS
(name it) (7)
2. Variation exists in stated phenotype of organ-
ism/ mutation occurs creating new alleles (name
the allele if applicable)
3. Some individuals have the selective advantage
(describe it)
4. Produces differential survival/ organisms with
successful alleles more likely to survive
5. Natural selection occurs via directional selec-
tion
6. Survivors breed and pass on alleles to offspring
7. Over time, there is a change in allele frequency
, AQA A-Level Biology Paper 2 2024/2025
20. Favours the mean phenotype. (Normal distribution Stabilising selection
becomes narrower)
21. Favours one extreme end. (Normal distribution Directional Selection
translates that way)
22. Favours both extreme phenotypes. Mean is at dis- Disruptive Selection
advantage and dies. Can create two new species
23. 1. Natural disaster Genetic Drift: Bottle-
2. Few survive neck Effect (4)
3. New population develops with different allele
4. Frequency to the original
24. Genetic drift that occurs after a small number of Founder effect
individuals colonize a new area. Allele frequency
is different to the original
25. 1. Populations geographically separated (forma- Allopatric speciation
tion of a river) (Allopatric Speciation) (4)
2. Separated populations now unable to reproduce
3. Different environments have different selective
pressures so each population will accumulate dif-
ferent beneficial mutations over time to help them
survive so change in allele frequency
4. Two populations become so genetically differ-
ent that they cannot reproduce to form fertile off-
spring, so are now classed as different species
26. Populations live in the same region but occupy Reproductive isola-
different habitats tion: Ecological
27. Same area but are sexually mature at different Reproductive isola-
times tion: Seasonal
28. Different species ensure successful mating by Reproductive Isola-
specific courtship (bird dances). As this is genetic, tion: Behavioural
mutation can change this
29.29.
, AQA A-Level Biology Paper 2 2024/2025
Plants exhibit pheromones to any mate with their Reproductive isola-
own species tion: Incompatibility
30. Lack of fit between sexual organs in insects Reproductive Isola-
tion: Incompatibility in
Arthropods
31. 1. Occurs in the same habitat so sympatric speci- Lord Howe Island in
ation the Tasman Sea pos-
2. Mutation causes different flowering times sesses two species
3. Seasonal Reproductive separation of palm tree which
4. No gene flow between the organisms so differ- have arisen via sym-
ent alleles passed on. patric speciation. The
5. Disruptive natural selection two species diverged
6. Eventually, different species cannot interbreed from each other after
to produce fertile offspring; the island was formed
6.5 million years ago.
The flowering times
of the two species are
different.
Using this informa-
tion, suggest how
these two species of
palm tree arose by
sympatric speciation.
(6)
32. 1. Colonisation by pioneer species Succession occurs in
2. Change in environment by organisms present natural ecosystems.
3. Enables other species to survive as the environ- Describe and explain
ment becomes less hostile how succession oc-
4. Increase in biodiversity curs. (6)
5. Stability increases
6. Leading to a climax community
33. 1. Collect sample, mark and release The mark-release-re-
2. Ensure marking does not affect survival of the capture method can
fish be used to estimate
3. Allow time for fish to randomly distribute before the size of a fish pop-
collecting the second sample (decide time based ulation (4)
1. Alleles that are neither dominant nor recessive to Codominant
one another, so both alleles are always expressed
in the phenotype.
2. The inheritance of a single gene Monohybrid inheri-
tance
3. Physical, behavioural, biochemical expression of Phenotype
an organisms genotype
4. The type of genes an individual has Genotype
5. Alles that is always expressed in the phenotype Dominant
6. Only expressed in the phenotype when homozy- Recessive
gous
7. both alleles are the same Homozygous
8. Both alleles for a specific gene are different Heterozygous
9. Position of a gene on a chromosome Loci
10. A set of instructions for a specific polypeptide Gene
11. Different forms of a gene Allele
12. 1. Expected ratios are probability Suggest four reasons
2. Sexual reproduction is random due to random why observed ratios
fusion of gametes and random assortment homol- are not the same as
ogous chromosomes. expected ratios (4).
3. Small sample size
4. Linked genes
13. 1. Homologous chromosomes pair up Meiosis results in
2. Crossing over / chiasmata form; cells that have the
3. Produces new combination of alleles haploid number of
4. Chromosomes separate at random chromosomes and
5. This produces varying combinations of genes show genetic varia-
6. Chromatids separated at meiosis II tion. Explain how. (6)
, AQA A-Level Biology Paper 2 2024/2025
14. 1. Refer to the specific individuals (using their Pedigree Questions
number) Mark Scheme (3)
2. Explain what happened with the genes (passed
on recessive/dominant)
3. Describe the genotype of your examples and
mention their phenotype (homozygous/heterozy-
gous etc)
15. Group of organisms of the same species occupy- Populations
ing a particular space at a particular time that can
potentially interbreed to produce fertile offspring.
16. The total number of genes of every individual in an Gene pool
interbreeding population.
17. How often an allele appears in a population. Allele frequency [def-
inition][Equation] (2)
desired allele/total alleles = allele frequency (deci-
mal form)
18. No emigration or immigration Hardy-Weingberg
No mutations Assumptions (4)
Mating is random
No natural selection
19. 1. Selection pressure exists in an environment Natural selection MS
(name it) (7)
2. Variation exists in stated phenotype of organ-
ism/ mutation occurs creating new alleles (name
the allele if applicable)
3. Some individuals have the selective advantage
(describe it)
4. Produces differential survival/ organisms with
successful alleles more likely to survive
5. Natural selection occurs via directional selec-
tion
6. Survivors breed and pass on alleles to offspring
7. Over time, there is a change in allele frequency
, AQA A-Level Biology Paper 2 2024/2025
20. Favours the mean phenotype. (Normal distribution Stabilising selection
becomes narrower)
21. Favours one extreme end. (Normal distribution Directional Selection
translates that way)
22. Favours both extreme phenotypes. Mean is at dis- Disruptive Selection
advantage and dies. Can create two new species
23. 1. Natural disaster Genetic Drift: Bottle-
2. Few survive neck Effect (4)
3. New population develops with different allele
4. Frequency to the original
24. Genetic drift that occurs after a small number of Founder effect
individuals colonize a new area. Allele frequency
is different to the original
25. 1. Populations geographically separated (forma- Allopatric speciation
tion of a river) (Allopatric Speciation) (4)
2. Separated populations now unable to reproduce
3. Different environments have different selective
pressures so each population will accumulate dif-
ferent beneficial mutations over time to help them
survive so change in allele frequency
4. Two populations become so genetically differ-
ent that they cannot reproduce to form fertile off-
spring, so are now classed as different species
26. Populations live in the same region but occupy Reproductive isola-
different habitats tion: Ecological
27. Same area but are sexually mature at different Reproductive isola-
times tion: Seasonal
28. Different species ensure successful mating by Reproductive Isola-
specific courtship (bird dances). As this is genetic, tion: Behavioural
mutation can change this
29.29.
, AQA A-Level Biology Paper 2 2024/2025
Plants exhibit pheromones to any mate with their Reproductive isola-
own species tion: Incompatibility
30. Lack of fit between sexual organs in insects Reproductive Isola-
tion: Incompatibility in
Arthropods
31. 1. Occurs in the same habitat so sympatric speci- Lord Howe Island in
ation the Tasman Sea pos-
2. Mutation causes different flowering times sesses two species
3. Seasonal Reproductive separation of palm tree which
4. No gene flow between the organisms so differ- have arisen via sym-
ent alleles passed on. patric speciation. The
5. Disruptive natural selection two species diverged
6. Eventually, different species cannot interbreed from each other after
to produce fertile offspring; the island was formed
6.5 million years ago.
The flowering times
of the two species are
different.
Using this informa-
tion, suggest how
these two species of
palm tree arose by
sympatric speciation.
(6)
32. 1. Colonisation by pioneer species Succession occurs in
2. Change in environment by organisms present natural ecosystems.
3. Enables other species to survive as the environ- Describe and explain
ment becomes less hostile how succession oc-
4. Increase in biodiversity curs. (6)
5. Stability increases
6. Leading to a climax community
33. 1. Collect sample, mark and release The mark-release-re-
2. Ensure marking does not affect survival of the capture method can
fish be used to estimate
3. Allow time for fish to randomly distribute before the size of a fish pop-
collecting the second sample (decide time based ulation (4)
