GCSE Biology (AQA)

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Homozygous & Heterozygous

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Inheritance, Variation and Evolution Reproduction

Homozygous & Heterozygous

1:25 Genetic Inheritance Terms
Spec 4.6.1.6
Previous Phenotype Next Genetic Crosses & Probability
  • Each gene has two copies of each allele, one from each parent.
  • Alleles are different versions of the same gene.
  • Eye color alleles example: capital B for brown eyes, lowercase b for blue eyes.
  • Discussion limited to blue and brown eyes; green eyes covered beyond GCSE level.
  • Allele combinations represented by two letters.
  • Possible allele combinations: BB for brown eyes, bb for blue eyes, or Bb (a mix of both).
  • Homozygous: having two alleles that are the same (BB or bb).
  • Heterozygous: having two different alleles (Bb).
  • "Homo" in homozygous means same; "hetero" in heterozygous means different.
  • Understanding the difference between homozygous and heterozygous is crucial for exams.

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