Chapter 23.2, Problem 1CYP

Summary Introduction

To write:

The characteristics of a pedigree for an autosomal dominant and autosomal recessive trait.

Introduction:

In a pedigree chart, affected family members are designated by solid circles or squares while carriers are shown by a spot in an open circle or square.

Autosomal Dominant inheritance will have at least one or both of the dominant allele in the genotype (Aa or AA) for it to be expressed. As one allele is sufficient for the phenotypic expression of the trait, there is no carrier. So, everyone in a family with the trait's genotype in consideration will be expressing the trait as well.

Autosomal Recessive inheritance will require both of the same alleles in the genotype (bb) for it to be expressed. The family members with a single recessive allele will be carriers of the condition or disease (Bb) and will not express the phenotype of (b).

As it requires two copies of the recessive allele for the condition to occur- one has to be inherited from maternal genes and the other has to be inherited from the paternal genes - so it is possible to inherit an autosomal recessive condition from unaffected parents. But both of the unaffected parents will be required to have at least one copy of concerned recessive allele, that is, they must be carriers, if not affected.