IGCSE Biology Paper-1: Specimen Questions with Answers 168 - 168 of 208

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Question 168



Human skin colour is controlled by several gene pairs. Let us assume here that there are just three gene pairs on different chromosomes and that for each pair there are two alleles-an incompletely dominant one that codes for melanin deposition and an incompletely recessive one that codes for no melanin deposition. If a very dark-skinned person marries a very light skinned woman, what will be the chance that their offspring will have very dark skin?


Choice (4)









  • Polygenic inheritance or qualitative inheritance is controlled by two or more genes in which dominant alleles have cumulative effect, with each dominant allele expressing a part of functional polypeptide and full trait is shown when all dominant alleles are present. Genes involved in this qualitative inheritance are called polygenes.
  • Examples of polygenic inheritance in humans include height, eye colour and skin colour. Physical traits that have polygenic inheritance are influenced by more than one gene and typically display a continuous distribution, such as a range of heights. Polygenic traits do not have the classic phenotypic ratios of Mendelian inheritance. Example Human skin colour, human height.
Intermediate (Mulatto)

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