Heredity: Crash Course Biology #9

So, I have this brother, John. You may have heard of him.

JOHN: Hi there!

HANK: As it happens, John and I have the exact same parents.

JOHN: Yes, Mom and Dad Green.

HANK: And since we have the same parents, it's to be expected

that John and I would have similar physical characteristics

because the source of our DNA is exactly the same.

JOHN: Hank and I share some genes, but nobody knew anything about chromosomes or DNA until

the middle of the 20th century. And people have been noticing that brothers tend to look

alike since like, people started noticing stuff or whatever.

HANK: That was very scientific, John.

JOHN: I will remind you that I am doing you a favor.

Heredity: it's basically just the passing on of genetic traits from parents to offspring.

Like John said, the study of heredity is ancient, although the first ideas about how the goods

are passed on from parents to kids were really really really really really really

wrong.

For instance, the concept that people were working with for nearly 2,000 years came from

Aristotle, who suggested that: We're each a mixture of our parents' traits,

with the father kind of supplying the life force to the new human and the mother

supplying the building blocks to put it all together.

Aristotle also thought that semen was like highly-purified

menstrual blood, which is why we still refer to "bloodlines" when

we're talking about heredity.

Anyway, since nobody had a better idea, and since nobody

really wanted to tangle with Aristotle, for hundreds of years

everybody just assumed that our parents' traits just sort of

blended together in us:

like if a black squirrel and a white squirrel fell in love and decided to start a family

together, their offspring would be gray.

The first person to really start studying and thinking about

heredity in a modern way was this Austrian monk named Gregor Mendel

and Mendel demonstrated that inheritance followed particular patterns.

In the mid-1800s, Mendel spent sort of an unhealthy amount of time grubbing around

in his garden with a bunch of pea plants, and through a series of experiments, crossing

the pea plants and seeing which traits got passed on and which didn't--he came up with

a framework for understanding how traits actually get passed from one generation to another.

So, to talk about Classical Genetics, which includes Mendel's