The accompanying pedigree shows the transmission of albinism (absence of skin pigment) in a human family.

What is the most likely mode of transmission of albinism in this family? 

Key Concepts

Pedigree Analysis

Pedigree analysis is a diagrammatic method used to trace the inheritance patterns of traits through generations in a family. It helps identify whether a trait is dominant, recessive, or linked to sex chromosomes. By examining the relationships and traits of family members, one can infer the likely mode of inheritance for specific genetic conditions.

Autosomal Recessive Inheritance

Autosomal recessive inheritance occurs when a trait is expressed only when an individual has two copies of the recessive allele, one inherited from each parent. In the case of albinism, if both parents are carriers (heterozygous) for the trait, there is a 25% chance with each pregnancy that their child will be affected. This mode of inheritance often results in affected individuals appearing in families without a prior history of the condition.

Dominant vs. Recessive Traits

In genetics, dominant traits require only one copy of the allele to be expressed, while recessive traits require two copies. If albinism were a dominant trait, it would appear in every generation, as affected individuals would pass the trait to their offspring. Understanding the distinction between these types of traits is crucial for interpreting pedigree charts and predicting inheritance patterns.