Sex linkage

Sex linkage is like a special way that traits, or characteristics, can be passed down from parents to their kids. It has to do with the fact that boys and girls have different chromosomes, which are like tiny instructions that tell our bodies what to do and how to grow.

Girls have two X chromosomes, while boys have one X chromosome and one Y chromosome. And sometimes, certain traits are carried on the X chromosome. When this happens, they are said to be sex-linked traits.

Let's say that your dad has a gene for red-green color blindness. This means that he has trouble telling the difference between the colors red and green. This gene is carried on the X chromosome.

Now, if your dad gives you his X chromosome, and you are a girl, you'll have two X chromosomes, one from each parent. This means that you have a second chance to get a different, working version of the color vision gene from your mom on your other X chromosome. So even if your dad's color blindness gene is there, you might not be color blind because your mom gave you a working copy of the gene.

But if your dad gives his X chromosome to a boy instead of a girl, the boy only has that one X chromosome. He doesn't have another chance to get a working version of the gene from his mom like a girl does. So if the boy inherited the color blindness gene from his dad, he will probably be color blind.

This is why some traits are much more common in boys than girls. Boys only have one X chromosome, so they can't get a second chance at getting a working copy of the gene. Girls, on the other hand, can have two X chromosomes, so if they get a broken gene from one parent, they might still have a working copy from the other parent.