Exam (elaborations)
Ocr A level biology paper 2
Ocr A level biology paper 2
[Show more]
Seller
Follow
Content preview
Ocr A level biology paper 2Homozygous - correct answer-When an organism carries two copies of the same alleles.
Heterozygous - correct answer-When an organism has two different alleles of the same
gene.
Genotype - correct answer-Description of an organism's alleles.
Phenotype - correct answer-Characteristics of an organism as a result of the expression of
its genotype and the environment.
Gene - correct answer-Section of a chromosome that codes for a polypeptide.
Allele - correct answer-Alternative version of the same gene.
Gene locus - correct answer-Location of a gene on a chromosome.
Dominant allele - correct answer-Allele that is always expressed in the phenotype.
Recessive allele - correct answer-Allele that is only expressed in the phenotype when there
are two of them i.e. in a homozygote.
Codominant allele - correct answer-Both alleles are expressed in the phenotype.
Multiple alleles - correct answer-More than 2 alleles for a particular gene.
Sex linkage - correct answer-Characteristic or trait controlled by a gene found on the sex
chromosomes.
Homologous chromosomes - correct answer-Pair of chromosomes that carry genes for the
same characteristics, at the same gene loci.
Autosome - correct answer-Any chromosome that is NOT a sex chromosome.
Autosomal linkage - correct answer-Genes coding for different characteristics, found on the
same non-sex chromosome, are said to be linked.
Independent assortment - correct answer-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 answer-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 answer-Individual who has an allele, often for a disease, which is not
expressed in the phenotype i.e. they are heterozygous.
True breeding - correct answer-Individuals that are true breeding are homozygous for a
particular characteristic or trait.
Epistasis - correct answer-A type of gene interaction, where the allele of one gene masks the
effect of the allele of a different gene.
Hemizygous - correct answer-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 answer-The range of differences in characteristics between organisms
Phencopy - correct answer-When environmental conditions alter the phenotype to resemble
the effects of genotypic change
Discontinuous variation - correct answer-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 answer-Variation where there are two extremes and all
possible intermediate forms. Determined by many genes (polygenic) and influenced by the
environment.
Etiolation - correct answer-When plants grow abnormally long and spindly because they are
not getting enough light.
Chlorosis - correct answer-When plants don't produce enough chlorophyll and turn yellow eg
due to lack of magnesium in the soil.
Artificial selection - correct answer-When humans select which individuals in a population to
breed together in order to get desirable traits.
Stabilising selection pressure - correct answer-Factor that reduces the range of phenotypes
by selecting against individuals with the extreme phenotype.
Selection pressure - correct answer-A factor that gives a greater chance of surviving to some
members of the population than others e.g. moth camouflage
Stabilising selection - correct answer-Types of selection that operates against the extremes
of the range of phenotypes so the population remains the same over time.
Directional selection - correct answer-Factor that selects individuals with an extreme
phenotype of a range of phenotypes so the population changes over time.
, Genetic drift - correct answer-The increase or decrease in the frequency of alleles as a result
of chance events.
Carrying capacity - correct answer-The maximum population size of a species that a
particular habitat can support over time.
Gene pool - correct answer-The sum of all the alleles in a population at a given time.
Genetic bottleneck - correct answer-An event, such as a natural disaster, that causes a large
reduction in the size of a population.
Founder effect - correct answer-What happens when a small number of individuals start a
new population and there is only a small number of alleles.
Species - correct answer-A group of similar organisms that can reproduce to give fertile
offspring.
Allopatric speciation - correct answer-Populations become geographically isolated and, as a
result of natural selection, form new species.
Sympatric speciation - correct answer-Formation of a new species without geographical
isolation.
Reproductive isolation - correct answer-Populations cannot breed successfully together
because of mechanical changes or behavioral changes.
Geographical isolation - correct answer-A physical barrier such as a mountain range or a
desert that prevents gene flow between populations.
Natural selection - correct answer-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 answer-Enzyme that cuts DNA molecules at a specific
sequence of bases.
Palindromic recognition site - correct answer-The specific sequence of bases where a
restriction enzyme will cut. The sequence of bases reads the same in opposite directions.
DNA ligase - correct answer-Enzyme which joins sections of DNA together, catalysing
condensation reaction.
Sticky ends - correct answer-When a restriction endonuclease cuts DNA and leaves
unpaired bases.
Vector DNA - correct answer-Used to transfer DNA into a cell eg a plasmid or bacteriophage.
Plasmid - correct answer-Small, circular molecule of DNA used to transfer DNA into cells.
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller modocko752. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £6.47. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
81298 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy revision notes and other study material for 14 years now