Since the parents have a normal phenotype, this disorder must be caused by a recessive allele.
The phenotype, in genetics, is a group of an organism's qualities or observable features. The phrase includes an organism's morphology, or physical shape and structure, as well as its physiological and biochemical characteristics, behaviour, and the outcomes of behaviour. An individual's observable traits that are the outcome of gene expression; the way a person with a certain genotype presents themselves clinically.
Each gene has two recessive alleles, which come from each parent, which are inherited by each person. For a recessive trait, the two recessive alleles of the gene that causes the characteristic must both be present for the trait to manifest. When only one copy of an allele is present, it does not result in any phenotype at all.
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