A hereditary disease is inherited as an autosomal recessive trait1. The wild-type allele of the disease gene produces a mature mRNA that is 1250 nucleotides (nt) long. Molecular analysis shows that the mature mRNA consists of four exons that measure 400 nt (exon 1), 320 nt (exon 2), 230 nt (exon 3), and 300 nt (exon 4). A mother and father with two healthy children and two children with the disease have northern blot analysis performed in a medical genetics laboratory. The results of the northern blot for each family member are shown here. Identify the genotype of each family member, using the sizes of mRNAs to indicate each allele. (For example, a person who is homozygous wild type is indicated as '1250/1250.')

Key Concepts

Autosomal Recessive Inheritance

Autosomal recessive inheritance refers to a pattern where two copies of a mutated gene (one from each parent) are necessary for an individual to express a trait or disease. In this case, both parents can be carriers of the recessive allele without showing symptoms, but they can pass the allele to their offspring. If a child inherits two recessive alleles, they will exhibit the disease, while those with at least one wild-type allele will be healthy.

Mature mRNA and Exons

Mature mRNA is the final form of messenger RNA that is translated into proteins, consisting of exons (coding regions) and lacking introns (non-coding regions). In this scenario, the mature mRNA is composed of four exons with specific nucleotide lengths, which contribute to the total length of 1250 nucleotides. The sizes of these exons are crucial for determining the presence of specific alleles in the family members based on the northern blot analysis.

Northern Blot Analysis

Northern blot analysis is a technique used to detect specific RNA sequences in a sample. It involves separating RNA by size through gel electrophoresis, transferring it to a membrane, and hybridizing it with labeled probes. In this context, the northern blot results will reveal the sizes of mRNAs present in each family member, allowing for the determination of their genotypes based on the presence of wild-type or mutated alleles.