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. <insert step 1: Begin by understanding the characteristics of X-linked recessive and X-linked dominant traits. X-linked recessive traits are more common in males, as they have only one X chromosome. Females must have two copies of the recessive allele to express the trait. X-linked dominant traits can affect both males and females, but females are more frequently affected due to having two X chromosomes.>
2. <insert step 2: For the X-linked recessive trait (pedigree a), start by identifying a male with the trait. Since males have only one X chromosome, they will express the trait if they inherit the recessive allele. Indicate this by shading the square representing the male.>
3. <insert step 3: In the same pedigree, ensure that a female carrier (heterozygous) is present. She will have one normal allele and one recessive allele. Indicate this by shading half of the circle representing the female. This female can pass the recessive allele to her sons, who will express the trait.>
4. <insert step 4: For the X-linked dominant trait (pedigree b), identify a female with the trait. Since females have two X chromosomes, they can express the trait if they have at least one dominant allele. Indicate this by shading the circle representing the female.>
5. <insert step 5: In the same pedigree, ensure that a male with the trait is present. Since males have only one X chromosome, they will express the trait if they inherit the dominant allele. Indicate this by shading the square representing the male. This male can pass the dominant allele to all his daughters, who will express the trait, but not to his sons.>

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.