AQA A level Biology Topic 7 – Genetics, populations, evolution and ecosystems notes (A* achieved)

AQA AL Biology notes Topic 7 – Genetics, populations, evolution and ecosystems
Topic 7 – Genetics, populations, evolution and ecosystems
Table of Content

7.1 Inheritance...................................................................................2
7.2 Populations..................................................................................5
7.3 Evolution may lead to speciation..................................................6
7.4 Ecosystem.....................................................................................8




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, AQA AL Biology notes Topic 7 – Genetics, populations, evolution and ecosystems

7.1 Inheritance
Genotype
 Genetic constitution of an organism
 Eg BB, Bb, bb (eye colour)
Phenotype
 Expression due to genotype and environment
 Eg brown eyes
 Explains why genetically identical twins may have diverging phenotypes, esp. as get older & are
exposed to more environmental stimuli
Allele
 Different version of a gene (sequence of bases different)
 In a diploid organism, alleles at specific locus may be either
o Homozygous
 Both alleles at specific locus on each homologous chromosome are the same
 Eg BB or bb
o Heterozygous
 Both alleles at specific locus on each homologous chromosome are different
 Eg Bb
 Alleles may be…
o Dominant
 In heterozygous state, it's the allele that is always expressed (in phenotype)
o Recessive
 In heterozygous state, it's the allele that isn't expressed in phenotype
 Only expressed if homozygous recessive or absence of dominate
o Codominant
 Both alleles are expressed (in phenotype)




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