Variation & Population genetics

  • Created by: livvvx
  • Created on: 23-01-19 14:05
The differences in characteristics or phenotypes that exist
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The physical appearance of an organism as a result of the interaction of its genotype and the environment
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The genetic make-up of an organism
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Interspecific Variation
BETWEEN different species
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Intraspecific Variation
WITHIN a species
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Causes of Variation
A)Environmental-predation,food chains etc, B)Genetic- meiosis, mutations, random fusion of gametes
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Genetic variation- Meiosis
Occurs in the formation of gametes(special sex cells) e.g. pollen grain, sperm. Cells of this type- genetically different from each other so meiosis major cause of infraspecific variation. Variation into gametes by crossing over&indepedent assortment
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Genetic variation- Random fertilisation of gametes
Which gamete fuses with which at fertilisation is a random process so produces new combos of alleles and the offspring are therefore genetically diff from their parents
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Genetic variation- Mutation
Mutation causes a change in the no. or sequence of bases in DNA. This produces a change in the characteristics of an organism which can be passed on.
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Mutagenic Agents
Outside factors that can increase the basic mutation rate. 1)High energy ionising radiation e.g.X-rays, UV light 2)Chemicals e.g.nitrogen dioxide
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Mutations- Addition/Deletion
An extra base is added or removed ,changes all the subsequent triplets after the mutation so diff amino acids chain sequence made=Frame shift mutation, one added/deleted base at start of sequence could alt every triplet in sequence
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Mutations- Substitution
1)Mis-sense=one amino acid changes, impact depends on role may change shape of protein-doesn't function properly.2)Nonsense=result in stop codon-stop polypeptide prematurely alt tertiary str.3)Silent=no diff due to degenerate nature of genetic code
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Mutations- Duplication
One or more bases are repeated. Produces a frame shift to the right
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Mutations- Inversion
group of bases becomes separated from DNA seq and rejoin at same position but in inverse order(back to front)-affects amino acid sequence coded for
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Mutations- Translocation
group of bases becomes separated from DNA seq on one chromosome and becomes inserted into DNA seq of same or a diff chromosome. Often has sig.effects leading to an abnormal phenotype
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A group of the same species living in the same habitat or ecosystem
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Gene pool
All the alleles in a population at a particular time
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Allele Frequency
the proportion of organisms in the population carrying a particular allele)
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Population assumptions for Hardy-Weinberg equation
-pop is large, -random mating,-experiencing no selection, -has no mutation, immigration or emigration
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p=freq of dominant allele, q=freq of recessive allele, p²=freq of homozygous dominant genotype, q²=freq of homozygous recessive genotype(or phenotype), 2pq=freq of heterozygous genotype
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Genetic Drift
the idea that allele frequencies can change simply due to chance
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Genetic drift- The founder effect
sometimes happens that a few organisms from a pop become isolated from rest e.g.when a small no.of individuals emigrate and colonise a new region
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Genetic drift- Genetic bottlenecks
when it is temporarily reduced to a very small no. and when the majority of individuals are killed. Could be due to chance even e.g. disease, flooding or interference by man -hunting.
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The physical appearance of an organism as a result of the interaction of its genotype and the environment



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The genetic make-up of an organism


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BETWEEN different species


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WITHIN a species


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