Ocr A level biology paper 2 EXAM QUESTIONS AND ANSWERS
UPDATED 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED
BEST EXAM SOLUTION TOP RANKED TO SCORE A+
Phenotype - CORRECT ANSWERS Characteristics of an organism as a result of the expression
of its genotype and the environment.
Gene - CORRECT ANSWERS Section of a chromosome that codes for a polypeptide.
Allele - CORRECT ANSWERS Alternative version of the same gene.
Gene locus - CORRECT ANSWERS Location of a gene on a chromosome.
Dominant allele - CORRECT ANSWERS Allele that is always expressed in the phenotype.
Recessive allele - CORRECT ANSWERS Allele that is only expressed in the phenotype when
there are two of them i.e. in a homozygote.
Codominant allele - CORRECT ANSWERS Both alleles are expressed in the phenotype.
Multiple alleles - CORRECT ANSWERS More than 2 alleles for a particular gene.
Sex linkage - CORRECT ANSWERS Characteristic or trait controlled by a gene found on the
sex chromosomes.
Homologous chromosomes - CORRECT ANSWERS Pair of chromosomes that carry genes for
the same characteristics, at the same gene loci.
Homozygous - CORRECT ANSWERS When an organism carries two copies of the same
alleles.
Heterozygous - CORRECT ANSWERS When an organism has two different alleles of the same
gene.
,Genotype - CORRECT ANSWERS Description of an organism's alleles.
Autosome - CORRECT ANSWERS Any chromosome that is NOT a sex chromosome.
Autosomal linkage - CORRECT ANSWERS Genes coding for different characteristics, found on
the same non-sex chromosome, are said to be linked.
Independent assortment - CORRECT ANSWERS During metaphase I of meiosis, the
arrangement of one pair of homologous chromosomes on the equator of the spindle is
independent of the arrangement of any other pair of chromosomes. A key event that
produces GENETIC VARIATION in gametes.
Crossing over - CORRECT ANSWERS Where chromatids twist around each other and
exchange genetic material. Happens during prophase I of meiosis which increases the
amount of GENETIC VARIATION in gametes by producing new combination of alleles.
Carrier - CORRECT ANSWERS Individual who has an allele, often for a disease, which is not
expressed in the phenotype i.e. they are heterozygous.
True breeding - CORRECT ANSWERS Individuals that are true breeding are homozygous for a
particular characteristic or trait.
Epistasis - CORRECT ANSWERS A type of gene interaction, where the allele of one gene
masks the effect of the allele of a different gene.
Hemizygous - CORRECT ANSWERS Having a single copy of a gene instead of the normal two.
For example, if there is heterozygous inheritance of the sex chromosomes, XY.
Variation - CORRECT ANSWERS The range of differences in characteristics between
organisms
Phencopy - CORRECT ANSWERS When environmental conditions alter the phenotype to
resemble the effects of genotypic change
,Discontinuous variation - CORRECT ANSWERS Variation where there are 2 or more distinct
categories with no intermediates. Determined by a small number of genes with little or no
environmental influence.
Continuous variation - CORRECT ANSWERS Variation where there are two extremes and all
possible intermediate forms. Determined by many genes (polygenic) and influenced by the
environment.
Etiolation - CORRECT ANSWERS When plants grow abnormally long and spindly because
they are not getting enough light.
Chlorosis - CORRECT ANSWERS When plants don't produce enough chlorophyll and turn
yellow eg due to lack of magnesium in the soil.
Artificial selection - CORRECT ANSWERS When humans select which individuals in a
population to breed together in order to get desirable traits.
Stabilising selection pressure - CORRECT ANSWERS Factor that reduces the range of
phenotypes by selecting against individuals with the extreme phenotype.
Selection pressure - CORRECT ANSWERS A factor that gives a greater chance of surviving to
some members of the population than others e.g. moth camouflage
Stabilising selection - CORRECT ANSWERS Types of selection that operates against the
extremes of the range of phenotypes so the population remains the same over time.
Directional selection - CORRECT ANSWERS Factor that selects individuals with an extreme
phenotype of a range of phenotypes so the population changes over time.
Genetic drift - CORRECT ANSWERS The increase or decrease in the frequency of alleles as a
result of chance events.
Carrying capacity - CORRECT ANSWERS The maximum population size of a species that a
particular habitat can support over time.
, Gene pool - CORRECT ANSWERS The sum of all the alleles in a population at a given time.
Genetic bottleneck - CORRECT ANSWERS An event, such as a natural disaster, that causes a
large reduction in the size of a population.
Founder effect - CORRECT ANSWERS What happens when a small number of individuals
start a new population and there is only a small number of alleles.
Species - CORRECT ANSWERS A group of similar organisms that can reproduce to give fertile
offspring.
Allopatric speciation - CORRECT ANSWERS Populations become geographically isolated and,
as a result of natural selection, form new species.
Sympatric speciation - CORRECT ANSWERS Formation of a new species without geographical
isolation.
Reproductive isolation - CORRECT ANSWERS Populations cannot breed successfully together
because of mechanical changes or behavioral changes.
Geographical isolation - CORRECT ANSWERS A physical barrier such as a mountain range or
a desert that prevents gene flow between populations.
Natural selection - CORRECT ANSWERS The mechanism of evolution.It is the survival of
individuals in a population to reproduce and pass on their alleles to the next generation.
Restriction endonuclease - CORRECT ANSWERS Enzyme that cuts DNA molecules at a
specific sequence of bases.
Palindromic recognition site - CORRECT ANSWERS The specific sequence of bases where a
restriction enzyme will cut. The sequence of bases reads the same in opposite directions.
DNA ligase - CORRECT ANSWERS Enzyme which joins sections of DNA together, catalysing
condensation reaction.
UPDATED 2024/2025 ALL ANSWERS 100% CORRECT VERIFIED
BEST EXAM SOLUTION TOP RANKED TO SCORE A+
Phenotype - CORRECT ANSWERS Characteristics of an organism as a result of the expression
of its genotype and the environment.
Gene - CORRECT ANSWERS Section of a chromosome that codes for a polypeptide.
Allele - CORRECT ANSWERS Alternative version of the same gene.
Gene locus - CORRECT ANSWERS Location of a gene on a chromosome.
Dominant allele - CORRECT ANSWERS Allele that is always expressed in the phenotype.
Recessive allele - CORRECT ANSWERS Allele that is only expressed in the phenotype when
there are two of them i.e. in a homozygote.
Codominant allele - CORRECT ANSWERS Both alleles are expressed in the phenotype.
Multiple alleles - CORRECT ANSWERS More than 2 alleles for a particular gene.
Sex linkage - CORRECT ANSWERS Characteristic or trait controlled by a gene found on the
sex chromosomes.
Homologous chromosomes - CORRECT ANSWERS Pair of chromosomes that carry genes for
the same characteristics, at the same gene loci.
Homozygous - CORRECT ANSWERS When an organism carries two copies of the same
alleles.
Heterozygous - CORRECT ANSWERS When an organism has two different alleles of the same
gene.
,Genotype - CORRECT ANSWERS Description of an organism's alleles.
Autosome - CORRECT ANSWERS Any chromosome that is NOT a sex chromosome.
Autosomal linkage - CORRECT ANSWERS Genes coding for different characteristics, found on
the same non-sex chromosome, are said to be linked.
Independent assortment - CORRECT ANSWERS During metaphase I of meiosis, the
arrangement of one pair of homologous chromosomes on the equator of the spindle is
independent of the arrangement of any other pair of chromosomes. A key event that
produces GENETIC VARIATION in gametes.
Crossing over - CORRECT ANSWERS Where chromatids twist around each other and
exchange genetic material. Happens during prophase I of meiosis which increases the
amount of GENETIC VARIATION in gametes by producing new combination of alleles.
Carrier - CORRECT ANSWERS Individual who has an allele, often for a disease, which is not
expressed in the phenotype i.e. they are heterozygous.
True breeding - CORRECT ANSWERS Individuals that are true breeding are homozygous for a
particular characteristic or trait.
Epistasis - CORRECT ANSWERS A type of gene interaction, where the allele of one gene
masks the effect of the allele of a different gene.
Hemizygous - CORRECT ANSWERS Having a single copy of a gene instead of the normal two.
For example, if there is heterozygous inheritance of the sex chromosomes, XY.
Variation - CORRECT ANSWERS The range of differences in characteristics between
organisms
Phencopy - CORRECT ANSWERS When environmental conditions alter the phenotype to
resemble the effects of genotypic change
,Discontinuous variation - CORRECT ANSWERS Variation where there are 2 or more distinct
categories with no intermediates. Determined by a small number of genes with little or no
environmental influence.
Continuous variation - CORRECT ANSWERS Variation where there are two extremes and all
possible intermediate forms. Determined by many genes (polygenic) and influenced by the
environment.
Etiolation - CORRECT ANSWERS When plants grow abnormally long and spindly because
they are not getting enough light.
Chlorosis - CORRECT ANSWERS When plants don't produce enough chlorophyll and turn
yellow eg due to lack of magnesium in the soil.
Artificial selection - CORRECT ANSWERS When humans select which individuals in a
population to breed together in order to get desirable traits.
Stabilising selection pressure - CORRECT ANSWERS Factor that reduces the range of
phenotypes by selecting against individuals with the extreme phenotype.
Selection pressure - CORRECT ANSWERS A factor that gives a greater chance of surviving to
some members of the population than others e.g. moth camouflage
Stabilising selection - CORRECT ANSWERS Types of selection that operates against the
extremes of the range of phenotypes so the population remains the same over time.
Directional selection - CORRECT ANSWERS Factor that selects individuals with an extreme
phenotype of a range of phenotypes so the population changes over time.
Genetic drift - CORRECT ANSWERS The increase or decrease in the frequency of alleles as a
result of chance events.
Carrying capacity - CORRECT ANSWERS The maximum population size of a species that a
particular habitat can support over time.
, Gene pool - CORRECT ANSWERS The sum of all the alleles in a population at a given time.
Genetic bottleneck - CORRECT ANSWERS An event, such as a natural disaster, that causes a
large reduction in the size of a population.
Founder effect - CORRECT ANSWERS What happens when a small number of individuals
start a new population and there is only a small number of alleles.
Species - CORRECT ANSWERS A group of similar organisms that can reproduce to give fertile
offspring.
Allopatric speciation - CORRECT ANSWERS Populations become geographically isolated and,
as a result of natural selection, form new species.
Sympatric speciation - CORRECT ANSWERS Formation of a new species without geographical
isolation.
Reproductive isolation - CORRECT ANSWERS Populations cannot breed successfully together
because of mechanical changes or behavioral changes.
Geographical isolation - CORRECT ANSWERS A physical barrier such as a mountain range or
a desert that prevents gene flow between populations.
Natural selection - CORRECT ANSWERS The mechanism of evolution.It is the survival of
individuals in a population to reproduce and pass on their alleles to the next generation.
Restriction endonuclease - CORRECT ANSWERS Enzyme that cuts DNA molecules at a
specific sequence of bases.
Palindromic recognition site - CORRECT ANSWERS The specific sequence of bases where a
restriction enzyme will cut. The sequence of bases reads the same in opposite directions.
DNA ligase - CORRECT ANSWERS Enzyme which joins sections of DNA together, catalysing
condensation reaction.
