Question

State the molecular function of the proteins encoded by each of the following genes. Briefly state how disruption of this gene results in the recessive phenotype.

• R gene in peas
• Y gene in peas
• Cystic Fibrosis

Answer 1

1. R gene:

Molecular function: The 'R' gene encodes for starch branching enzyme-1 (SBE-1) which is somehow responsible for round phenotype of pea.

Disruption of this gene leads to: If the R gene is disrupted, the resultant recessive (r) phenotype is wrinkled green pea.

Reason: Round and wrinkled seeds differed in the quantity and shape of the starch grains that occurred in storage cells in the cotyledons. It was found out in later studies that wrinkled seeds lack SBE-1 gene or have dysfunctional form of this gene which results into complex metabolic changes in starch, lipid, and protein biosynthesis in the seed.

2. Y gene:

Molecular function: Imparts color to the peas. If the gene is functional (Y), the color of the pea is yellow.

Disruption of this gene leads to: The recessive trait due to lack of this gene (y) leads to the phenotype of green colored peas.

Reason: The gene imaparting yellow color (Y), which is dominant, if absent, cannot be expressed, or is dysfunctional or if it is mutant can lead to green colored peas.

3. CFTR gene (Cystic fibrosis gene):

Molecular function: CFTR (cystic fibrosis transmembrane conductance regulator) gene codes for CFTR protein. The product of this gene (the CFTR protein) is a chloride ion channel important in creating sweat, digestive juices, and mucus.

Disruption of this gene leads to: A single mutation/ mutation in one allele does not affect the individual, but if both the alleles are mutated it results into a genetic disorder cystic fibrosis.

Reason: The common mutation and the common cause of this disease is the mutation in the three nucleotides at 508th position. This leads to many complications, but the major organ being affected are lungs. The accumulated mucus makes it difficult to breathe.