Topic Summaries

Inheritance terminology

GCSE > Biology > WJEC > GCSE Biology Topic Summaries > DNA synthesis and inheritance > Inheritance terminology
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  • Gene: a section of DNA that codes for a particular protein.
  • Allele: two versions of the same gene located at the same place on a chromosome.
  • Gamete: sex cells that contain half the number of chromosomes of all other cells with male and female gametes combining in fertilisation.
  • Chromosome: structures of DNA found in the nucleus of eukaryotic cells.
  • Dominant: an allele that is always expressed, so a characteristic will show if inherited from either parents. Dominant alleles are written as capitals (e.g. 'B' for brown eyes).
  • Recessive: an allele that will only be expressed and show a characteristic if two copies are present, one from each parent. Recessive alleles are written as lower case letters (e.g. 'b' for blue eyes).
  • Homozygous: a genotype with two of the same alleles (e.g. 'BB' or 'bb'). 
  • Heterozygous: a genotype with two different alleles (e.g. 'Bb').
  • Genotype: the collection of genes/alleles present in an organism.
  • Phenotype: the physical characteristics of an organism, determined by the genotype and environment (e.g. if the genotype is Bb, the phenotype is brown eyes).
  • Polygenetic inheritance: some characteristics are controlled by a single gene (e.g. fur colour in mice, red-green colour blindness in humans) but most characteristics are a result of the interaction of multiple genes, rather than a single gene.

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