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Hey, welcome to another biology video.
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Today we are going to examine a couple of experiments that took place back in the early part of the 20th century.
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And these experiments helped us understand that it is, in fact, dna that causes traits to be expressed in organism and that can pass those traits to other organisms, to the offspring.
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And so the first experiment was in the 1920s by a guy named griffith, and he took the bacteria that will cause pneumonia in mice, streptococcus pneumonia comes in two types.
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Type r does not make the mice sick.
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Type s does make the mice sick.
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So what he did was he would kill, the type s, the kind that makes the mice sick, add it to the type r, and then inject those two together into a mouse or a population of mice.
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And so what he found was that when you had the living type r plus the dead type s, the mice still got sick.
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So there had to be something in the s strain that was being transmitted to the r strain that then caused the r to change its traits...