In order to have a disorder caused by a recessive allele;the person must have what genotype?

The genotype must be a homozygous recessive allele.

Explanation: A recessive allele is a gene which lacks the ability to manifest itself outwardly in the presence of a dominant gene. A homozygous allele is a pair of gene made up of two identical genes which can either be recessive or dominant. Examples of a homozygous allele is AA, aa, BB, bb.

For a recessive allele to manifest outwardly, it must be homozygous for example aa, bb, tt. If a recessive allele is heterozygous such as in Bb, (b) which is recessive will not be able to express itself phenotypically because the dominant allele (B) will overshadow its effect.

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