Linkage disequilibrium

Linkage disequilibrium (LD) means that certain genes that are close together on a chromosome tend to be inherited together more often than if they were randomly distributed. It's like if you have a set of toys that you always play with together and never separate, even though they don't necessarily have anything to do with each other.

Imagine you have a big toy box with different types of toys in it. Now, you want to pick three toys to play with: a red ball, a blue car, and a green doll. If you had no LD, each toy would be chosen completely at random each time. However, if the red ball and the blue car were always found together, you would be more likely to pick both of them instead of one or the other. Likewise, if the green doll was always found alone, you would be less likely to pick it with the other toys.

In the same way, if two genes are often inherited together, they can "act" like they are one gene. This can make it harder to do genetics because you can't tell which gene is causing the effect you're seeing - it could be one gene or both of them working together. LD can also be used to find out if two genes are close together on a chromosome, which can be helpful for finding the genetic causes of diseases.

So basically, linkage disequilibrium means that some genes like to stick together and hang out, which can make it harder to figure out which ones are doing what.