Classical Genetics (Khan Academy)

How can we study inheritance?

When spending time with your own family, friends, and neighbors, you may have noticed that many traits run in families. For instance, members of a family may share similar facial features, hair color (like the brother and sister below), or a predisposition to health problems such as diabetes. Characteristics that run in families often have a genetic basis, meaning that they depend on genetic information a person inherits from his or her parents.

Image credit “Brother, sister, portrait, russet,” by Adina Voicu (CC0, public domain).

What if you wanted to figure out how genetic information is transmitted between generations? For instance, you might be curious how traits can “skip” a generation, or why one child in a family may suffer from a genetic disease while another does not. How could you go about asking these kinds of questions scientifically?

An obvious first idea would be to study human inheritance patterns directly, but that turns out to be a tricky proposition (see the pop-up below for details). In this article, we’ll see how a nineteenth-century monk named Gregor Mendel instead uncovered the key principles of inheritance using a simple, familiar system: the pea plant.

[Why didn’t Mendel study humans?]

Many of us are curious about genetics because we want to understand human inheritance. If the burning questions of genetics are about humans, why would anyone study inheritance in something like the pea plant?

When it comes to basic principles of inheritance, humans may be the organisms we most want to learn about, but they aren’t always the best organisms to study experimentally. For instance, it takes many years for a human being to grow, mature, and have children, making data collection slow. Also, when humans have children, they often have one or two (rather than, say, several thousand), making it harder to see mathematical patterns in the data. Finally, and perhaps most critically, it wouldn’t be possible (or ethical) to set up controlled experiments in human genetics – that is, you couldn’t ask a pair of people to have children just because you were curious what those children would look like.