Question

in his transformation experiments, which of the following results did griffith observe?

mutant mice were resistant to bacterial infections.

mixing a heat - killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.

mixing a heat - killed nonpathogenic strain of bacteria with a living pathogenic strain makes the pathogenic strain nonpathogenic.

infecting mice with nonpathogenic strains of bacteria makes them resistant to pathogenic strains.

Explanation:

Griffith's experiment involved Streptococcus pneumoniae. He found that when he mixed a heat - killed pathogenic (S - strain) with a living non - pathogenic (R - strain) bacteria, the non - pathogenic bacteria could be transformed into the pathogenic form. This was because the heat - killed S - strain released some genetic material (later identified as DNA) that was taken up by the R - strain.

• The first option about mutant mice is not related to Griffith's key finding.
• The third option is incorrect as mixing heat - killed non - pathogenic with living pathogenic does not make the pathogenic non - pathogenic.
• The fourth option about infecting with non - pathogenic making mice resistant is not what Griffith observed. His focus was on the transformation of bacteria, not mouse resistance development in that way.

Answer:

Mixing a heat - killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.