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? 

Verified step by step guidance

1. Analyze the pedigree to determine the inheritance pattern. Look for key indicators such as whether the trait skips generations, affects both sexes equally, or is passed from parent to child directly.
2. Recall that albinism is typically caused by mutations in genes involved in melanin production, such as the TYR gene. It is often inherited in an autosomal recessive manner, meaning two copies of the mutated gene are required for the trait to manifest.
3. Check if individuals with albinism in the pedigree have parents who do not exhibit the trait. This would suggest that the parents are carriers (heterozygous) for the recessive allele.
4. Verify if the trait affects both males and females equally in the pedigree. If it does, this supports the hypothesis of autosomal inheritance rather than sex-linked inheritance.
5. Conclude that the most likely mode of transmission is autosomal recessive if the above criteria are met. If the pedigree does not match these characteristics, consider alternative modes of inheritance such as autosomal dominant or X-linked recessive.

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 or recessive, and whether it is linked to sex chromosomes. By examining the pedigree, one can determine how albinism is passed down and predict its occurrence in future generations.

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 albinism allele, 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.

Phenotype vs. Genotype

The phenotype refers to the observable characteristics or traits of an organism, such as skin pigmentation, while the genotype is the genetic makeup that determines these traits. In the context of albinism, individuals with the phenotype of albinism have a specific genotype that includes two recessive alleles. Understanding the distinction between these concepts is crucial for interpreting the pedigree and determining the mode of inheritance.