Which of the following statements about Hfr cells and bacterial conjugation is false?

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Question: Which of the following statements about Hfr cells and bacterial conjugation is false?

Option 1: 'An F' plasmid contains some bacterial genes.' This is true. When an F' plasmid forms, it carries along adjacent bacterial genes, so the plasmid itself includes bacterial DNA in addition to the F factor.

Option 2: 'An Hfr cell becomes an F- cell if its integrated F plasmid is excised.' This is nuanced but can be considered true in a typical treatment of the topic. If the F factor excises cleanly from the chromosome, the cell can revert to F-; however, if the excision is imprecise, it can take adjacent bacterial genes with it to form an F' plasmid, so the outcome is not exclusively F- in all cases. In standard exam contexts, this statement is often treated as true because excision can yield an F- cell when no bacterial genes are carried away.

Option 3: 'Cells with integrated F' plasmid have two copies of some genes.' This is true. When the F factor is integrated into the chromosome, the host may end up with a partial diploid (merodiploid) for genes located near the integration site, effectively giving two copies of those genes.

Option 4: 'If excision of the F plasmid from an Hfr cell includes some bacterial genes, a partial diploid can result.' This is true. Imprecise excision can pull adjacent chromosomal genes into the excised F plasmid, creating a partial diploid situation in the donor.

Option 5: 'The genes that are transferred from an Hfr cell into a recipient cell during conjugation replace the equivalent genes in the recipient cell.' This statement is false. During conjugation, transferred DNA can recombine with the recipient's chromosome, potentially introducing new alleles or creating merodiploidy, but it does not simply replace the recipient’s existing genes in a wholesale, locus-for-locus manner. Recombination can lead to replacement of specific alleles, but the transfer process itself does not universally overwrite the recipient’s genes in a one-to-one replacement; also not all transferred segments are perfectly integrated. Therefore, this blanket claim of direct replacement is misleading and incorrect.

In summary, the only statement that mischaracterizes the transfer process as a simple gene-for-gene replacement is Option 5; the other statements align with established concepts about F, Hfr, F' plasmids, and partial diploidy.

Which of the following statements about Hfr cells and bacterial conjugation is false?Single choice

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