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Cellular Control
DNA Genetic Code

Transcription and Translation
Transcription: creation of single-stranded mRNA copy of DNA coding strand.
Translation: the assembly of polypeptides at ribosomes.
Genes code for polypeptides such as:
· structural proteins (collagen and keratin)
· haemoglobin
· immunoglobulins
· cell surface receptors
· channel proteins
· enzymes.…

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I. Molecule of RNA binds to ribosome. Two codons (a codon is three bases,
one codon codes for an amino acid) attach to small subunit on the
ribosome, exposed to the large subunit. First exposed codon
is always AUG. Using ATP energy and an enzyme, a tRNA
w/ methionine…

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Mutation: change in the amount of, or
arrangement of, the genetic material
in a cell.
· May be a mutation to the DNA, for
example base deletion, addition or
substitution or by inversion/repeat of
a triplet.
· Chromosome mutation involves
change to the structure of a
· Mutations…

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Biological Processes

Meiosis and its significance
The chromosome number in gametes needs to be haploid. Meiosis achieves this through two
separate divisions, which each have four stages.
There is an interphase during which DNA replication takes place.
Meiosis I:
Prophase I
· Chromatin condenses, supercoil, shorten and thicken. Come together…

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Allele: a version of a gene, an allele of the gene has a difference in DNA base sequence that is
expressed as a slightly different polypeptide.
Locus: the position of a gene on a chromosome.
Crossing over: lengths of DNA are swapped from one chromatid to another.
Meiosis increases genetic…

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Homeobox genes are arranged in
Hox clusters.
· Nematodes (roundworms) have
1 Hox cluster.
· Drosophila has 2 Hox clusters.
· Vertebrates have 4, of 9-11
genes on separate
Increase in Hox clusters probably
arose by duplication of a single
complex present in segmented
worms, and has allowed more…

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Figure 6 - The process of apoptosis. Hydrolytic enzymes are released from lysosomes inside the cell,
which then results in chromatin condensing and the cell shrinking. Organelles become tightly packed. The
membrane forms blebs and DNA breaks into fragments. The cell breaks into vesicles which are then taken
up by…

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Using genetic diagrams
Problems involving sex linkage -
Haemophilia A - Several factors needed for blood to clot following wound, one is a protein, factor
VIII, coded for by a gene on the X chromosome. Recessive allele expresses a protein that does
not function. Males that suffer from haemophilia re…

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Problems involving codominance -
Sickle-cell anaemia - -strands of Hb differ
by one animo acid at position 6, when
abnormal Hb is deoxygenated it is not
soluble and becomes crystalline and
aggregates to more linear structures,
deforms red blood cells so can no longer
squeeze through capillaries. After many

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Population genetics
The Hardy-Weinberg Principle
Mathematical model to calculate the allele frequencies in populations for traits with dominant and
recessive alleles.
· Population is very large.
· Mating is random.
· No selective advantage for any genotype.
· There is no mutation, migration, or genetic drift.
The frequency of…


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