ExpertEasy1 markShort Answer
AQA GCSE · Question 01.4 · Inheritance Variation and Evolution
What is the phenotype of a person with the genotype Nn?
What is the phenotype of a person with the genotype Nn?
How to approach this question
Recall the symbols given: N is the allele for not having MSUD, and n is the allele for MSUD. The allele N is dominant. A phenotype is the observable characteristic. Determine the characteristic of a person with one dominant allele (N) and one recessive allele (n).
Full Answer
Unaffected / without MSUD / not having MSUD
The genotype is Nn. This means the person has one dominant allele (N) and one recessive allele (n). The dominant allele masks the effect of the recessive allele. Since N is the allele for *not* having MSUD, this is the characteristic that will be expressed. Therefore, the person's phenotype is unaffected by MSUD.
Common mistakes
✗ Giving the genotype (Nn) instead of the phenotype.
✗ Stating they have MSUD. This would only happen with the genotype nn.
✗ Describing them as a "carrier". While true, "unaffected" is the correct description of the phenotype.
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