Use the blank pedigrees provided to depict transmission of (a) an X-linked recessive trait and (b) an X-linked dominant trait, by filling in circles and squares to represent individuals with the trait of interest. Give genotypes for each person in each pedigree. Carefully design each transmission pattern so that pedigree (a) cannot be confused with autosomal recessive transmission and pedigree (b) cannot be confused with autosomal dominant transmission. Identify the transmission events that eliminate the possibility of autosomal transmission for each pedigree.

Key Concepts

X-linked Inheritance

X-linked inheritance refers to the pattern of genetic transmission of traits located on the X chromosome. In X-linked recessive traits, males (XY) are more likely to express the trait since they have only one X chromosome, while females (XX) can be carriers if they have one affected X. In contrast, X-linked dominant traits can affect both males and females, but males often exhibit more severe symptoms due to their single X chromosome.

Pedigree Analysis

Pedigree analysis is a method used to trace the inheritance patterns of traits through generations in a family tree format. Circles represent females and squares represent males, with filled shapes indicating individuals expressing the trait. This visual representation helps identify whether a trait is autosomal or X-linked by observing the distribution of the trait among genders and generations.

Distinguishing Autosomal from X-linked Traits

To distinguish between autosomal and X-linked traits in pedigrees, one must observe the pattern of inheritance. Autosomal recessive traits typically skip generations and can affect both genders equally, while X-linked recessive traits often show a male bias and do not pass from father to son. X-linked dominant traits, on the other hand, appear in every generation and affect both genders, but affected males cannot pass the trait to their sons, which is a key distinguishing feature.