The figure below depicts changes to the amount of DNA present in a recipient cell that is engaged in conjugation with an Hfr cell. Hfr cell DNA begins entering the recipient cell at Time A. Assume that reciprocal crossing over occurs (in other words, a fragment of the recipient's chromosome is exchanged for a homologous fragment from the Hfr cell's DNA).
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What process is occurring at Time C that is decreasing the DNA content?
A) crossing over
B) cytokinesis
C) degradation of DNA that was not retained in the recipient's chromosome
D) reversal of the direction of conjugation

Question

The figure below depicts changes to the amount of DNA present in a recipient cell that is engaged in conjugation with an Hfr cell. Hfr cell DNA begins entering the recipient cell at Time A. Assume that reciprocal crossing over occurs (in other words, a fragment of the recipient's chromosome is exchanged for a homologous fragment from the Hfr cell's DNA). 
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What process is occurring at Time C that is decreasing the DNA content?
A) crossing over 
B) cytokinesis 
C) degradation of DNA that was not retained in the recipient's chromosome 
D) reversal of the direction of conjugation

Quizplus · Accepted Answer

The decrease in DNA content at Time C is due to the degradation of DNA that was not retained in the recipient's chromosome. During conjugation, only a portion of the Hfr cell's DNA is transferred to the recipient cell, with the rest being degraded. Therefore, the decrease in DNA content at Time C suggests that the recipient cell has already retained the maximum amount of DNA from the Hfr cell, and any remaining Hfr DNA is being degraded.

The Figure Below Depicts Changes to the Amount of DNA