Topic 18 - Variation Flashcards
Why does variation occur?
Genetic and environmental factors
What are examples of genetic variation
Mutation, meiosis, random fertilisation of gametes.
Disruptive selection
When individuals high contain the allele coding for either of the extreme traits and more likely to survive and pass on their alleles. Can lead to speciation
Speciation
Creates new species hen original population of same species becomes reproductively isolated.
Allopathic speciation
Populations become geographically separated leading to speciation because they are unable to reproduce due to the geographical barrier, continuing to accumulate different beneficial mutations genetic differences make them unable to interbreed to create fertile offspring
Sympatric speciation
Populations become reproductively isolated due to differences in behaviour leading to speciation (no due to the geographical barrier). Could be due to random mutation that could impact reproductive behaviour e.g different courtship rituals or different fertile windows. This means there will be no gene flow between populations. Reproductively isolated populations accumulate different mutations, genetic differences in DNA make them unable to interbreed to create fertile offspring
Genetic drift
Change in the allele frequency within a population between generations.
What is genetic mutation
The random change tot he structure of a DNA molecule (gene mutation) or the structure or number of chromosomes (chromosome mutation)
2 main events in meiosis that cause variation
Independent assortment - of homologous chromosomes causes variation between gametes
Crossing over - between the non sister chromatids of homologous chromosomes
What is the random fertilisation of gametes
Where two gametes meet by chance, contributing to the novel combination of genes
