Northern blot analysis is performed on mRNA produced by transcription of a gene

Question

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-type allele, and alleles n1and n2 are each recessive alleles. Results of northern blot analysis of organisms with six different genotypes are shown.

a. Organisms with the genotypes NN Nn2, and n2n2 each have single bands with the same electrophoretic mobility. Thinking about the composition of mRNA, explain this observation.

b. Organisms that are n1n1have a single mRNA band with higher electrophoretic mobility. Thinking about the composition of mRNA, explain this observation.

c. Two mRNA bands are detected for organisms with the Nn1and the n1n2genotypes. Explain this observation.

Explanation / Answer

Based on the given data,

a.

In the genotype “NN” both alleles are same, hence they code same type of mRNA, in the genotype Nn2, one allele is dominant wild type and another one is recessive, in this condition only dominant allele expresses, hence same mRNA like “NN” is synthesized. In the third case both alleles are recessive (n2n2) and may be they also synthesize same mRNA like wild type allele. Hence, all these three genotypes have same kind of mRNA with same chemical composition.

b.

Organisms that are “n1n1” have a single mRNA band, but has higher electrophoretic mobility because the n1 allele may encode smaller mRNA than NN Nn2, and n2n2 genotypes.

c.

So, based on above results, N, n2 encode same type of mRNA, only n1 alone encode different type of mRNA and expresses, irrespective of N allele expression. Hence, two mRNA bands are detected for organisms with the Nn1and the n1n2genotypes.

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