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Evolutionary Biology

Molecular evolution

QuestionAnswer
How do changes occur? • Point mutation • Recombination • Duplication (of genes or chromosomes) • Chromosome rearrangements
Point mutation Changes at a single nucleotide base • Normally a mistake during DNA replication • Can also be caused by exposure to x- rays, UV, certain chemicals
Types of point mutation • Substitution mutations Transitions Transversions • Insertions • Deletions
Diseases caused by said mutations - point mutation: sickle cell anaemia - frameshifts: HIV, crohn's
In coding DNA - Synonymous substitutions accumulate at a faster rate than non-synonymous substitutions - Transitions accumulate faster than transversions
Rates of substitution - Low rate of substitution at non-degenerate sites (where mutations cause amino acid sequence changes) - High rate of substitution at degenerate sites (which do not change the amino acid sequence)
Recombination Based on alignment of DNA in homologous chromosomes during meiosis (cell division to produce gametes)
Recombination and the evolution of sex - only occurs in sexually reproducing species
Duplication of sections of DNA • Unequal crossing over • Transposition (back to later) • Non-segregation of chromosomes during cell division
Genome duplication (polyploidy) • Increase in chromosome number (>2n) • Due to failed separation of chromosomes in meiosis
Chromosome rearrangement - translocation - rare - movement of DNA between non-homologous chromosomes
Chromosome rearrangement - inversion End-to-end re-arrangement of a chromosome segment
Gene conversion • DNA change is countered by repair - ‘proof reading' enzymes carry this out
Horizontal gene transfer • Inheritance of DNA from parents to offspring = vertical transmission
Summary changes during replication, or unrepaired DNA damage –Point mutation – Recombination – Duplication – Chromosome rearrangements
Summary Changes resulting from DNA repair – Gene conversion
Summary Acquisition of ‘new’ DNA – Transposition – Horizontal gene transfer – Hybridisation
Created by: reub8n
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