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Summary Genetics, Variation, and Relationships Between Organisms notes
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- AQA
Unit 4: Genetics, Variation, and Relationships Between Organisms summary pages for AQA A level biology
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GeneticInformation,
Variation, and
Relationships
Between
Organisms
Genetic Information
DNA Structure
● Double Helix:
● Composed of two antiparallel strands.
● Held together by hydrogen bonds between complementary base pairs
(A-T, G-C).
● Nucleotides:
● Phosphate, deoxyribose sugar, and nitrogenous base.
, DNA Replication
● Semi-Conservative:
● Each new DNA molecule contains one original and one newly
synthesized strand.
● Enzymes:
● DNA helicase unwinds the double helix.
● DNA polymerase adds complementary nucleotides.
Protein Synthesis
● Transcription:
● DNA is transcribed into mRNA.
● Takes place in the nucleus.
● Translation:
● mRNA is translated into a polypeptide chain.
● Takes place in ribosomes.
● Genetic Code:
● Triplet code; each triplet codes for a specific amino acid.
Genetic Variation
● Meiosis:
● Reduces chromosome number by half.
● Produces genetically unique gametes.
● Crossing Over:
● Exchange of genetic material between homologous chromosomes.
● Mutation:
● Source of new alleles and genetic diversity.
Variation and Selection
Types of Selection
● Stabilising Selection:
● Favours the average phenotype.
● Directional Selection:
● Favours one extreme phenotype.
● Disruptive Selection:
● Favours both extreme phenotypes.
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