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.

Verified step by step guidance

1. Step 1: Understand the inheritance patterns of X-linked traits. X-linked recessive traits are typically expressed in males (XY) who inherit the affected X chromosome, while females (XX) are usually carriers unless they inherit two affected X chromosomes. X-linked dominant traits are expressed in both males and females, but females may have a higher likelihood of being affected due to having two X chromosomes.
2. Step 2: For pedigree (a) (X-linked recessive trait), depict a male with the trait (affected X chromosome) and ensure that his daughters are carriers (one affected X chromosome and one normal X chromosome). His sons should not inherit the trait since they receive the Y chromosome from their father. This transmission pattern eliminates the possibility of autosomal recessive inheritance because autosomal traits do not depend on sex chromosomes.
3. Step 3: For pedigree (b) (X-linked dominant trait), depict an affected father passing the trait to all his daughters (since they inherit his affected X chromosome) but not to his sons (since they inherit his Y chromosome). This transmission pattern eliminates the possibility of autosomal dominant inheritance because autosomal traits would affect both sons and daughters equally.
4. Step 4: Assign genotypes to each individual in both pedigrees. For pedigree (a), affected males should have the genotype X^aY, carrier females should have the genotype X^AX^a, and unaffected individuals should have genotypes X^AY or X^AX^A. For pedigree (b), affected individuals should have the genotype X^AX^A or X^AY, and unaffected individuals should have genotypes X^AX^A or X^AY.
5. Step 5: Carefully label the transmission events in each pedigree that eliminate the possibility of autosomal inheritance. For pedigree (a), highlight the absence of male-to-male transmission and the carrier status of females. For pedigree (b), emphasize the father-to-daughter transmission and the absence of father-to-son transmission.

Key Concepts

X-linked Inheritance

X-linked inheritance refers to the pattern of genetic transmission where genes are 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 females may show milder symptoms due to the presence of a second, normal X chromosome.

Pedigree Analysis

Pedigree analysis is a method used to trace the inheritance patterns of traits through generations in a family tree. Squares represent males and circles represent females, with filled shapes indicating individuals expressing the trait. By analyzing the connections and affected individuals, one can determine whether a trait is autosomal or X-linked, as well as dominant or recessive, based on the patterns of inheritance observed.

Distinguishing Autosomal from X-linked Traits

To distinguish between autosomal and X-linked traits, one must observe the inheritance patterns. For X-linked recessive traits, affected males cannot pass the trait to their sons but can pass it to daughters, who may become carriers. In contrast, X-linked dominant traits can be passed from an affected parent to both sons and daughters. Autosomal traits, however, show a more uniform distribution across genders, making it crucial to identify these patterns in pedigree analysis.