AQA · Biology · 8461
GCSE Biology: Genetic inheritance
Inheritance, variation and evolution · AQA GCSE Biology (8461), specification point 4.6.1.6. Cards are generated from the exam board's own specification for "Genetic inheritance", and every card links back to the page it came from. Specification © AQA — used with attribution.
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What is an allele?
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A different form (version) of a gene.
What is meant by an organism's genotype?
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The alleles present in the organism for a given gene or trait.
What is meant by an organism's phenotype?
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The characteristics that are expressed (observable), produced by the genotype acting at a molecular level.
When is a dominant allele expressed in the phenotype?
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Always — even if only one copy is present.
When is a recessive allele expressed in the phenotype?
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Only if two copies are present, so no dominant allele is present.
An organism with two identical alleles for a trait is ? for that trait.
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homozygous
An organism with two different alleles for a trait is ? for that trait.
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heterozygous
Give one example of a characteristic controlled by a single gene.
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Fur colour in mice (or red-green colour blindness in humans).
Are most characteristics controlled by a single gene or multiple genes?
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Multiple genes interacting — single-gene inheritance is the exception.
What is a Punnett square diagram used for?
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To show the possible allele combinations of offspring in a genetic cross and predict the probability of each outcome.
What is a gamete?
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A sex cell (e.g. sperm or egg) that carries one copy of each chromosome and fuses with another gamete at fertilisation.
What is a gene?
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A section of DNA on a chromosome that codes for a particular characteristic (protein).
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