Griffith's Experiment/Bacterial Transformation (Griffith's Experiment)

Have you ever wondered what determines your height, hair and skin color and even the size of your nose?

It’s DNA, the genetic material of cell. But do you know how it has been proved?

Here are the experiments that proved it.

Griffith’s Experiment:

Griffith took two strains of pneumococcus bacteria.

1. S (III) – which have smooth polysaccharide capsule, giving smooth colonies (S) and is virulent causing pneumonia.

AND

2. R (II) – which have no capsule, giving Rough colonies (R) and is avirulent unable to cause pneumonia.

When the virulent S (III) bacteria injected in mice, it killed them causing pneumonia.

But when the Avirulent R (II) injected in mice, the mice lives

If you inject the heat killed virulent S (III) bacteria, the mice still live. Implying that live S (III) bacteria are needed for causing pneumonia

But interestingly, when mice were injected with the mixture of heat killed virulent S (III) bacteria and avirulent R (II) bacteria, mice died.

Analysis of dead mice reveals live S (III) virulent bacteria suggesting something form the heat killed S (III) had transformed to the live avirulent R (II) bacteria, responsible for the transformation of the live avirulent bacteria to virulent S (III) bacteria, causing death of mice. This is called as Bacterial Transformation.

To prove DNA is genetic material, team of Avery et al and Hershey and chase performed another experiments. See other video for it.

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