A2 Biology F215: Control, Genomes & Environment - REVISION CARDS

28 pages of revision cards, really really handy! Pretty much everything you need to revise this exam. I always take them to college before an exam because they are lightweight but still have all the information you need to jog your memory!

:-)

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A gene is a length of DNA ­ i.e. it is a ·Three bases code for an amino acid. There ·Transcription is the creation of a single stranded
sequence of nucleotide bases that codes for are four bases giving 64 possible codes ­ more mRNA copy of the DNA coding strand.
polypeptides which make up proteins e.g. than enough for the 20 amino acids required for ·Transcription: the DNA base sequence is copied to
a messenger (m) RNA base sequence by
enzymes. making proteins.
complementary base pairing (A-U and G-C).
A section of DNA is called a gene. ·A section of DNA is called a gene. ·Gene to be transcribed unwinds and unzips, H
Genes are a sequence of DNA bases that code ·Genes are a sequence of DNA bases that code bonds break.
for a sequence of amino acids, a polypeptide. for a sequence of amino acids, a polypeptide. ·RNA nucleotides bind with H bonds to template
DNA is NOT a protein. ·DNA is NOT a protein. strand. (RNA polymerase helps)
·mRNA produced is a copy of coding strand and a
complementary copy of template strand.
·mRNA released and leaves nucleus to cytoplasm
to a ribosome.
·If the changed code still puts the correct amino
·DNA mutations: changes to the sequence of
acid in the protein, or if the incorrect amino acid Translation: the mRNA attaches to a ribosome
bases when DNA is replicating ­ e.g. in
has no effect, it is a neutral mutation. Also know and transfer (t) RNA pairs with mRNA to bring
meiosis, gametes pass mutation on.
as a silent mutation. the right amino acid to the correct place in a
·A mutation in the DNA is a change in the
protein.
amount of (e.g. addition or deletion of a bases Translation is the assembly of proteins at the
or bases) or the arrangement of DNA ribosome.
(substitution of a base). Transfer RNA (tRNA) brindgs the correct amino acid,
·A chromosome mutation involves changes to ribosomal RNA (rRNA) ensures the correct tRNA H
the whole or part of the chromsome, e.g. bonds with mRNA and enables adjacent amino acids
inversion (leg of chromosome breaks off, turns to form peptide bonds. This is catalysed by enzymes.
180 and attaches back), or deletion. tRNA with anticodon that complements a stop codon
·Non-disjunction = when chromosomes fail to does NOT bring an amino acid so the polypeptide
separate in meiosis 1. ends.
·Chiasma is not an example of a mutation
·Mutations may be harmful (e.g. sickle cell Cyclic AMP activates proteins by changing
mutation ­ anaemia) but also beneficial (e.g. Operons control protein production ­ e.g. lac
their 3D structure. Once a protein has been
sickle cell in heterozygotes resistance to malaria). operon in prokaryotes.
made by transcription and translation (also It is a length of DNA made up of structureal genes
·Some mutations can be beneficial e.g.the called gene expression) it may need cAMP (genes that code proteins e.g. for enzxymes) and
mutation that caused skin to be paler was an before it can carry out its function. control sites. The control sites in the lac operon are
advanatge because people with pale skin living in called promoter and operator regions. The operator
countries with little sunshine can make more It is also a second messenger in the cell. and promoter are both genes as they are lengths of
vitamin DN than people with darker skin. However (communication role). DNA but they do not code for polypeptides. But are
in sunny countries people with darker skjin have essential for the production of the structural genes.
the advanateg as there is enough sunlight to
make vit D and they won't get skin cancer.
Because the environment changes, variation in a
population allows natural selection to occur.…read more

Slide 2

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How does DNA code for amino acids?
What is a gene
Describe transcription
gene
Describe translation
What is a DNA mutation?
What is a silent mutation
What is a chromosome mutation?
What is an operon What is cyclic AMP? Describe how mutations can
be both beneficial and
harmful…read more

Slide 3

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Two divisions: first is where chromosome pairs P1: homologous chromosomes pair up and at the Similar methods can produce
split up; second produces four new haploid cells chiasma and can swap sections of chromatid ­ recombinant DNA (DNA of one
(gametes). crossing-over.
·The resulting daughter ceklls have half the Homologous pairs form a bivalent, they have the
organism combined with that of another)
original number of chormosomes and are same genes at the same loci, but the alleles that in genetic engineering.
haploid and can be used for sexual each homologue carries may be different. Isolation of gene by restriction enzyme
reproduction. (endonuclease),
·After Interphase meiosis involves: Prophase Complementary sticky ends formed
1; Metaphase 1; Anaphase 1; and Telophase
1. Then second division (P2, M2, A2, T2).
Seal sugar phosphate backbone using
ligase.
·Varied combinations of alleles in gametes can M1: chromosome pairs can line up to give many
·Genotype is the combination of alleles in an
occur in P1 and M1. Gametes fuse (fertilisation) combinations when they separate ­
organism (e.g. Aa, AA or aa). Phenotype is the
giving more variation in genotype of offspring. independent assortment.
characteristic that is expressed.
·P1 formation of chiasma Independent assortment of bivalents, paternal and
·M1 random assortment of bivalents maternal chromosomes can be lined up in any order.
·M2 random segregation of sister chromatids In meiosis 2 sister chromatids can undergo random
assortment, so incorporating further genetic variation.
·Fertilisation random fusion of gametes
·Mutation.
Co-dominant is when both alleles are expressed. ·An allele is a version of a gene ­ a dominant
·The position of a gene on a chromosome is its locus. An in-between or mixed phenotype results e.g. IAIB allele (A) shows in the phenotype while a
If a gene locus is on (carried on) the X or Y gives blood group AB, not A or B. recessive allele (a if present) does not (unless
chromosome it is known as sex-linkage.
homozygous; aa). Dominant alleles are
expressed in the phenotype when only one is
·Linkage: two genes on the same chromosome; present.
ratio would differ ­ e.g. 3:1 for two main (parental) ·Remember a recessive allele on the X
types with very small numbers of two non- chromosome (sex linked) will be expressed in
parental (from crossing-over). males since they only have one copy. (i.e. XY
·This means if nose and ear shape on same and gene not carried on Y chromosome).
chromosome then unless chiasma form, it is likely
if you inherit your fathers nose you will also have
your fathers ear.…read more

Slide 4

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What is
recombinant What happens in Prophase 1 What is the basis of meiosis
DNA? How
is it made?
What happens in Metaphase 1 When can genetic variation occur in meiosis What is a genotype
What is an allele? What is codominant What is a locus?
What is linkage?…read more

Slide 5

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If two genes (loci) are on the same ·Continuous variation is due to many genes (e.g. a ·Natural selection is when the variant best
chromosome (linkage), crossing-over (see P1 range of heights); discontinuous variation is due to suited to the environment reproduce more and
card 29) can break the linkage to produce one gene (e.g. blood groups A, B, AB or O). increase in frequency within the population.
Environment (e.g. nutrition) as well as genes
recombinants. ·Variation in a population
(genotype) will contribute to phenotype variation.
·Crossing over is when part of the non-sister ·Selection pressure that causes one variant to
chromatids is swapped in Prophase 1 of have an advantage.
meiosis 1. Chiasma is the name of the point at ·The variant individual with the advantage is
which they join. (just before the part of the more likely to survive and therefore reproduce
chromosome is swapped). and therefore pass on their mutated alleles to
the next generation. This continues over many
generations increasing the frequency of this
allele in the population.
·Non-reproductive cloning includes copying ·If environment is constant, existing best
·If environment changes (e.g. antibiotics given
DNA in bacterial plasmids and producing variant (e.g. white coats in arctic animals) will
to bacteria), resistant variants will be selected
genetically identical cells in other organisms (e.g. continue to be selected ­ stabilising selection.
(increase in population) ­ directional selection.
stem cells). It is not the production of a whole new If populations or variants are isolated
organism. But the formation of cloned cells. (ecological, seasonal or reproductive), selection
will produce a new species (speciation).
·Examples include bacteria and Fungi can be ·The host egg is implanted into the uterus of the
surrogate mother. The baby is genetically ·Reproductive cloning transfers the
cultured.
identical to the donor (e.g. Dolly the sheep). nucleus from a donor adult (somatic) cell to
·Why use these microorganisms:
The above are all methods of artificial cloning. an egg that has no nucleus (host egg).
·Grow rapidly (many generations in short time.
Artificial cloning also includes taking cuttings or ·A new organism is made that is a clone of
·Can be genetically engineered to produce specific
grafting plants onto others to give new ones e.g. the parent. That provided the nucleus. The
product.
Natural cloning ­ identical twins, vegetative mitochondrial DNA will be from the animal
·Produce products into surrounding medium for
propagation in elm trees. that provided the egg cell. This technique is
easy harvesting
illegal in humans, but has been done in
·Can be grown anywhere in world don't depend on
sheep and mice.
climate.
·Products in more pure form
·Can be grown on medium that would be toxic or
useless to humans.
·Grow well at low temperatures…read more

Slide 6

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What is continuous variation
What is natural selection What is crossing over?
What is a chiasma
What is directional selection What is stabilising selection What is non-reproductive cloning
What is reproductive cloning What is artificial cloning What organism is used to
produce gene product…read more

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