AQA A-LEVEL BIOLOGY PAPER 2 EXAM
COMPLETE QUESTIONS AND CORRECT
DETAILED ANSWERS (VERIFIED
ANSWERS) |ALREADY GRADED
A+||BRAND NEW!!
Alleles that are neither dominant nor recessive to one another, so both alleles are
always expressed in the phenotype. - Answer - Codominant
The inheritance of a single gene - Answer - Monohybrid inheritance
Physical, behavioural, biochemical expression of an organisms genotype - Answer -
Phenotype
The type of genes an individual has - Answer - Genotype
Alles that is always expressed in the phenotype - Answer - Dominant
Only expressed in the phenotype when homozygous - Answer - Recessive
both alleles are the same - Answer - Homozygous
Both alleles for a specific gene are different - Answer - Heterozygous
Position of a gene on a chromosome - Answer - Loci
A set of instructions for a specific polypeptide - Answer - Gene
Different forms of a gene - Answer - Allele
1. Expected ratios are probability
2. Sexual reproduction is random due to random fusion of gametes and random
assortment homologous chromosomes.
3. Small sample size
,4. Linked genes - Answer - Suggest four reasons why observed ratios are not the same
as expected ratios (4).
1. Homologous chromosomes pair up
2. Crossing over / chiasmata form;
3. Produces new combination of alleles
4. Chromosomes separate at random
5. This produces varying combinations of genes
6. Chromatids separated at meiosis II - Answer - Meiosis results in cells that have the
haploid number of chromosomes and show genetic variation. Explain how. (6)
1. Refer to the specific individuals (using their number)
2. Explain what happened with the genes (passed on recessive/dominant)
3. Describe the genotype of your examples and mention their phenotype
(homozygous/heterozygous etc) - Answer - Pedigree Questions Mark Scheme (3)
Group of organisms of the same species occupying a particular space at a particular
time that can potentially interbreed to produce fertile offspring. - Answer - Populations
The total number of genes of every individual in an interbreeding population. - Answer -
Gene pool
How often an allele appears in a population.
desired allele/total alleles = allele frequency (decimal form) - Answer - Allele frequency
[definition][Equation] (2)
No emigration or immigration
No mutations
Mating is random
No natural selection - Answer - Hardy-Weingberg Assumptions (4)
1. Selection pressure exists in an environment (name it)
2. Variation exists in stated phenotype of organism/ 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 selection
6. Survivors breed and pass on alleles to offspring
7. Over time, there is a change in allele frequency - Answer - Natural selection MS (7)
, Favours the mean phenotype. (Normal distribution becomes narrower) - Answer -
Stabilising selection
Favours one extreme end. (Normal distribution translates that way) - Answer -
Directional Selection
Favours both extreme phenotypes. Mean is at disadvantage and dies. Can create two
new species - Answer - Disruptive Selection
1. Natural disaster
2. Few survive
3. New population develops with different allele
4. Frequency to the original - Answer - Genetic Drift: Bottleneck Effect (4)
Genetic drift that occurs after a small number of individuals colonize a new area. Allele
frequency is different to the original - Answer - Founder effect
1. Populations geographically separated (formation of a river) (Allopatric Speciation)
2. Separated populations now unable to reproduce
3. Different environments have different selective pressures so each population will
accumulate different beneficial mutations over time to help them survive so change in
allele frequency
4. Two populations become so genetically different that they cannot reproduce to form
fertile offspring, so are now classed as different species - Answer - Allopatric speciation
(4)
Populations live in the same region but occupy different habitats - Answer -
Reproductive isolation: Ecological
Same area but are sexually mature at different times - Answer - Reproductive isolation:
Seasonal
Different species ensure successful mating by specific courtship (bird dances). As this is
genetic, mutation can change this - Answer - Reproductive Isolation: Behavioural
Plants exhibit pheromones to any mate with their own species - Answer - Reproductive
isolation: Incompatibility
COMPLETE QUESTIONS AND CORRECT
DETAILED ANSWERS (VERIFIED
ANSWERS) |ALREADY GRADED
A+||BRAND NEW!!
Alleles that are neither dominant nor recessive to one another, so both alleles are
always expressed in the phenotype. - Answer - Codominant
The inheritance of a single gene - Answer - Monohybrid inheritance
Physical, behavioural, biochemical expression of an organisms genotype - Answer -
Phenotype
The type of genes an individual has - Answer - Genotype
Alles that is always expressed in the phenotype - Answer - Dominant
Only expressed in the phenotype when homozygous - Answer - Recessive
both alleles are the same - Answer - Homozygous
Both alleles for a specific gene are different - Answer - Heterozygous
Position of a gene on a chromosome - Answer - Loci
A set of instructions for a specific polypeptide - Answer - Gene
Different forms of a gene - Answer - Allele
1. Expected ratios are probability
2. Sexual reproduction is random due to random fusion of gametes and random
assortment homologous chromosomes.
3. Small sample size
,4. Linked genes - Answer - Suggest four reasons why observed ratios are not the same
as expected ratios (4).
1. Homologous chromosomes pair up
2. Crossing over / chiasmata form;
3. Produces new combination of alleles
4. Chromosomes separate at random
5. This produces varying combinations of genes
6. Chromatids separated at meiosis II - Answer - Meiosis results in cells that have the
haploid number of chromosomes and show genetic variation. Explain how. (6)
1. Refer to the specific individuals (using their number)
2. Explain what happened with the genes (passed on recessive/dominant)
3. Describe the genotype of your examples and mention their phenotype
(homozygous/heterozygous etc) - Answer - Pedigree Questions Mark Scheme (3)
Group of organisms of the same species occupying a particular space at a particular
time that can potentially interbreed to produce fertile offspring. - Answer - Populations
The total number of genes of every individual in an interbreeding population. - Answer -
Gene pool
How often an allele appears in a population.
desired allele/total alleles = allele frequency (decimal form) - Answer - Allele frequency
[definition][Equation] (2)
No emigration or immigration
No mutations
Mating is random
No natural selection - Answer - Hardy-Weingberg Assumptions (4)
1. Selection pressure exists in an environment (name it)
2. Variation exists in stated phenotype of organism/ 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 selection
6. Survivors breed and pass on alleles to offspring
7. Over time, there is a change in allele frequency - Answer - Natural selection MS (7)
, Favours the mean phenotype. (Normal distribution becomes narrower) - Answer -
Stabilising selection
Favours one extreme end. (Normal distribution translates that way) - Answer -
Directional Selection
Favours both extreme phenotypes. Mean is at disadvantage and dies. Can create two
new species - Answer - Disruptive Selection
1. Natural disaster
2. Few survive
3. New population develops with different allele
4. Frequency to the original - Answer - Genetic Drift: Bottleneck Effect (4)
Genetic drift that occurs after a small number of individuals colonize a new area. Allele
frequency is different to the original - Answer - Founder effect
1. Populations geographically separated (formation of a river) (Allopatric Speciation)
2. Separated populations now unable to reproduce
3. Different environments have different selective pressures so each population will
accumulate different beneficial mutations over time to help them survive so change in
allele frequency
4. Two populations become so genetically different that they cannot reproduce to form
fertile offspring, so are now classed as different species - Answer - Allopatric speciation
(4)
Populations live in the same region but occupy different habitats - Answer -
Reproductive isolation: Ecological
Same area but are sexually mature at different times - Answer - Reproductive isolation:
Seasonal
Different species ensure successful mating by specific courtship (bird dances). As this is
genetic, mutation can change this - Answer - Reproductive Isolation: Behavioural
Plants exhibit pheromones to any mate with their own species - Answer - Reproductive
isolation: Incompatibility
