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7 Genetics, Populations, Evolution & Ecosystems AQA A-Level Biology 🐒…
7 Genetics, Populations, Evolution & Ecosystems AQA A-Level Biology 🐒
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Evolution
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genetic varation can occur through mutation, meiosis & random fertilisation of gametes, predation. disease & competition over survival result in differential survival and reproduction --> nartural selection
speciation -variation due to mutation can cause organisms with phenotypes providing selective advantages due to different selection pressures and produce offspring and pass on their favourable alleles to the next generation increasing the allele frequency in the gene pool/population this change in allele frequency in a population can cause evolution reproductive seperation of gene pools can cause accumulation of difference in their gene pools so new species arise as they are unable to interbreed with the original population and produce fertile offspring
stabalising selection phenotypes with successful characterisitcs are preserved and the genetic diversity is reduced and selection does not occur due to change in environement so individuals closest to mean are favoured
directional selection is when indiviuals adapt to one extreme to survive in changed environmental conditions
disruptive selection is when individuals whihc contains the alleles to code for either extreme trait are more likely to survive due to a change in environemnt
allopatric speciation geographic isolation through separation of two gene pools so can no longer interbreed sympatric speciation not geographically isolated reproductive isolation due to chromosomal error during cell division other reasons could be mutations that change courtship behaviour that isn't recognised or anatomical changes that stop sexual reproduction
genetic drift change in allele frequency within a population between generations the smaller the population the bigger the impact on allele frequency which is why evolution occurs more rapidly in small populations
Exam Question How could selection of one gene increase rapidly? IF it was a dominant allele always expressed
Exam Question Sympatric Speciation: occurs in same habitat, mutations cause x, leading to reproductive isolation/ gene pools separate, so different alleles passed/frequency of alleles changed, eventually dif. species cannot breed to produce fertile offspring
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Definitions
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autosomal linkage genes that are located on the same chromosomes (not the sex chromosomes) *always linked to dihybrid) Aa Bb
episatisis when one gene modifies or masks the expression of a different gene at a different locus EE Bb
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population all the individuals of one species in one area at one time that can interbreed to make fertile offpring
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