Genotype: GCSE Biology Definition

Emma Archbold

Written by: Emma Archbold

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What is genotype?

In GCSE biology, a genotype is the combination of alleles that an organism has for a particular gene. The genotype of an organism interacts with environmental factors to determine an organism’s phenotype.

Each individual has two alleles of each gene, one from each of the homologous chromosomes inherited from its parents. This means that an organism’s genotype can be either:

  • homozygous dominant: two dominant alleles

  • heterozygous: two different alleles

  • homozygous recessive: two recessive alleles

Genotype is often represented using letters, where capital letters represent dominant alleles and lowercase letters represent recessive alleles, e.g. for a gene with the alleles B and b the genotypes for the following individuals would be:

  • homozygous dominant = BB

  • heterozygous = Bb

  • homozygous recessive = bb

 Genotype revision resources to ace your exams

You can explore genotype further using our GCSE revision notes, topic questions and flashcards for your specific exam board:

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Emma Archbold

Author: Emma Archbold

Expertise: Biology

Prior to working at SME, Emma was a Biology teacher for 5 years. During those years she taught three different GCSE exam boards and two A-Level exam boards, gaining a wide range of teaching expertise in the subject. Emma particularly enjoys learning about ecology and conservation. Emma is passionate about making her students achieve the highest possible grades in their exams by creating amazing revision resources!

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