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What is a mutation? A change in a base sequence of DNA of an organism
What are the types of mutation?
Substitution<div>Deletion </div><div>Addition </div><div>Chromosome
mutation</div>
What happens in substitution? One base is changed for another
How much damage is substitution likely to do, and why? Very little, as the DNA
code is degenerate, meaning a change in one base and no others will likely code for
the same amino acid, and so do no damage whatsoever
How does deletion/addition work? A base is removed from the sequence or added to
the sequence
How much damage is a deletion/addition mutation likely to do and why? A lot, as it
causes a frame shift mutation. This means that since the number of bases has
changed, the reading frame of three bases is shifted along, meaning all of the
triplets after the point of mutation will be changed to potentially different amino
acids, almost definitely meaning the protein is not functional
What is a chromosome mutation? Changes in the structure or number of whole
chromosomes
What is non-disjunction? A type of chromosome mutation where chromosomes fail
to separate during meiosis, meaning half of the gametes have one extra chromosome
and half of the gametes are missing one chromosome
What is meiosis used for? The production of gametes
How many daughter cells does meiosis produce? 4
What kind of cells does meiosis produce? Haploid
Why is meiosis important? So that haploid cells are produced, each with half
the number of chromosomes, so two can fuse in fertilisation to produce a diploid
cell, instead of one with too many chromosomes. Meiosis also produces a lot of
diversity through crossing over and independent assortment
What happens in meiosis 1? The homologous chromosomes pair up and line up on the
equator in a random fashion<div>The chromatids of the homologous pairs wrap around
each other</div><div>Then the homologous chromosomes separate and the cell divides,
producing two daughter cells that have a haploid number of chromosomes, and a
diploid amount of DNA</div>
What happens in meiosis 2? The chromatids are split, meaning 4 daughter cells
are produced, each with a haploid number of chromosomes and haploid amount of
DNA
What is independent assortment? When the homologous pairs line up on the
equator in meiosis 1, this happens in a random fashion, meaning either paternal or
maternal could be on either side, and either daughter cell could receive each. As
such, the combination of chromosomes and so alleles each daughter cell receives is
random, increasing variety
What is crossing over? In meiosis 1, when the homologous chromosomes line up, the
chromatids wrap themselves around each other, and cross over at points known as
chiasmata. At these chiasmata, there is tension, and the chromatids break off this
bit of DNA and swap them between chromosomes, creating new combinations of alleles,
increasing variety
How do you work out the total number of possible independent assortment
combinations? 2<sup>n</sup> where n is the number of homologous pairs
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