In a diploid organism, alleles at a specific locus may be homozygous or heterozygous
Diploid organisms carry two copies of every gene. When both copies are the same allele, the organism is homozygous. When the two copies differ, it is heterozygous.
Real World
Cystic fibrosis carriers are heterozygous (Ff) — they carry one faulty CFTR allele but show no symptoms, which is why the NHS newborn screening programme tests babies even when parents appear completely healthy.
Exam Focus
Write 'homozygous dominant' or 'homozygous recessive' — never just 'homozygous' without specifying which allele.
Evaluation Scaffold
A four-step framework for high-quality evaluation. Use this for 'assess', 'evaluate', and 'to what extent' questions.
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