6. In a transformation experiment, donor DNA from an E. coli strain with the genotypes was used to transform a strain of genotype Z⁺Y⁺. The frequencies of transformed classes were:
Z⁺ Y⁺               200
Z⁺ Y^–                400
Z^– Y⁺                400
Total               1000

What is the frequency (%) with which Y locus is co- transformed with the Z locus?
(1) 1            (2) 20
(3) 33.3        (4) 40

Experiment Overview

In this E. coli transformation experiment, donor DNA from a Z⁺Y⁺ strain transforms a Z⁻Y⁻ recipient. The transformed classes show Z⁺Y⁺: 200, Z⁺Y⁻: 400, and Z⁻Y⁺: 400 out of 1000 total transformants. Cotransformation frequency measures how often both Z⁺ and Y⁺ markers transfer together on the same DNA fragment, indicating genetic linkage. The formula uses the proportion of double transformants (Z⁺Y⁺) among all Z⁺ recipients.​

Step-by-Step Calculation

Total Z⁺ transformants equal Z⁺Y⁺ plus Z⁺Y⁻: 200 + 400 = 600. Z⁺Y⁺ double transformants number 200. Frequency = (200 / 600) × 100 = 33.3%. This value reflects linkage; closer loci yield higher cotransformation.​​

Option Analysis

• Option (1) 1%: Far too low; ignores actual data ratio, possibly confusing with rare events.​

• Option (2) 20%: Incorrect; matches 200/1000 (overall double transformants), not Z⁺-specific cotransformation.​

• Option (3) 33.3%: Correct; precisely (Z⁺Y⁺ / total Z⁺) × 100 = 33.3%.​

• Option (4) 40%: Wrong; no data supports this (e.g., not 400/1000), likely misread frequencies.​

Correct Answer: (3) 33.3. This CSIR NET-style question tests bacterial genetics mapping via transformation.​