9700 · 17.1
Variation flashcards
Revision flashcards for Cambridge 9700 Variation (syllabus 17.1). Flip, recall, then mark a real past-paper question.
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Genetic vs environmental variation?
Genetic: inherited allele differences. Environmental: non-inherited effects of external factors during lifetime.
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Continuous variation example?
Human height — polygenic, many alleles with additive effects, influenced by nutrition; shows normal distribution.
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Discontinuous variation example?
ABO blood groups — distinct categories, few genes, largely unaffected by environment.
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What is crossing over?
Exchange of DNA between non-sister chromatids of homologous chromosomes in prophase I of meiosis.
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What is independent assortment?
Random alignment and separation of homologous chromosome pairs in meiosis I, creating diverse gametes.
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What is the gene pool?
All alleles of all genes present in a population at a given time.
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Why is variation important for evolution?
Provides phenotypic diversity on which natural selection acts when environments change.
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What is a mutation?
A spontaneous change in DNA sequence; ultimate source of new alleles and genetic variation.