Recessive isn’t always bad. In fact, many (maybe all) genetic traits have a dominant and a recessive information.

For example peas. Let’s say there is a gene for colour. The dominant variation of the colour gene carries the information “green”. Let’s call this gene c for colour. Then there is a recessive variation with the information yellow.

We’ll write the dominant information as capital C and the recessive as lowercase c.

Now there is a pea with the genetic information CC (one from each parent). That’s a green pea.

Then there is one with Cc (father green, mother yellow). But you see the pea and it looks just like a green pea. Because the green gene C is dominant and the yellow c is recessive. You don’t know, that this is a mixed variety.

If two seemingly green peas pollinate each other, but under the hood, they are Cc, then they might produce a cc yellow pea.

For a lot of genetic information that’s not a problem, they are just different characteristics and not harmful.

But if you have B = your blood coagulates normally, and b = your blood doesn’t thicken, you just bleed out and die when you have a paper cut…

Then inheriting b from both of your parents is a terrible fate. This happened in the House of Saxe-Cobourg and other nobility in the 19th century.