Consider the three pedigrees below, all involving a single human trait.

Which combination of conditions, if any, can be excluded? dominant and X-linked dominant and autosomal recessive and X-linked recessive and autosomal

Verified step by step guidance

1. Step 1: Identify the pattern of affected individuals in each pedigree. Note the sex of affected individuals (squares for males, circles for females) and whether the trait appears in every generation or skips generations.
2. Step 2: For autosomal dominant traits, affected individuals usually appear in every generation and both males and females are equally likely to be affected. Check if this pattern fits any of the pedigrees.
3. Step 3: For X-linked dominant traits, affected males pass the trait to all daughters but no sons, and affected females can pass it to both sons and daughters. Look for affected females in every generation and affected males passing the trait to daughters.
4. Step 4: For autosomal recessive traits, the trait can skip generations, and affected individuals can have unaffected parents. Both males and females are equally affected. Check if the trait appears in siblings but not parents.
5. Step 5: For X-linked recessive traits, more males are affected than females, and affected males usually inherit the trait from carrier mothers. Affected males do not pass the trait to sons but can pass the allele to daughters who become carriers. Look for this pattern in the pedigrees.

Key Concepts

Modes of Inheritance

Modes of inheritance describe how traits are passed from parents to offspring. Common types include autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive. Each mode has distinct patterns in pedigrees, such as affected individuals in every generation for dominant traits or skipping generations for recessive traits.

Pedigree Analysis

Pedigree analysis involves studying family trees to track the inheritance of traits. Squares represent males, circles represent females, and shaded symbols indicate affected individuals. By examining affected and unaffected members across generations, one can infer the likely mode of inheritance.

X-linked vs Autosomal Traits

X-linked traits are associated with genes on the X chromosome and often show different patterns between males and females, such as males being more frequently affected in X-linked recessive traits. Autosomal traits are located on non-sex chromosomes and typically affect males and females equally.