Chapter 10, Problem 33P

Northern blot analysis is performed on mRNA produced by transcription of a gene in organisms with different genotypes. Three alleles occur at the gene: N is a dominant wild $\text{-}$ type allele, and alleles ${\text{n}}_{\text{1}}$ and ${\text{n}}_{\text{2}}$ are each recessive alleles. Results of northern blot analysis of organisms with six different genotypes are shown.

Organisms with the genotypes NN, ${\text{Nn}}_{\text{2}}$, and ${\text{n}}_{\text{2}}{\text{n}}_{\text{2}}$ each have single bands with the same electrophoretic mobility. Thinking about the composition of mRNA, explain this observation.

Organisms that are n₁n₁ have a single mRNA band with higher electrophoretic mobility. Thinking about the composition of mRNA, explain this observation.

Two mRNA bands are detected for organisms with the ${\text{Nn}}_{\text{1}}$ and the ${\text{n}}_{\text{1}}{\text{n}}_{\text{2}}$ genotypes. Explain this observation.