In this video, we're going to talk about the X linked recessive pedigrees. And so X linked recessive pedigrees are of course going to be pedigrees that depict an X linked recessive disorder. Typically, these X linked recessive pedigrees show that more males are going to be affected than females. Also, females of an X linked recessive pedigree can only be affected if the father is affected and the mother is either affected or at least a carrier or is at least heterozygous for the disorder. All sons of an affected female will be affected when it comes to X linked recessive disorders.
If we take a look at our example below, we can see a pedigree of an X linked recessive disorder. We can label this as an X linked recessive disorder, specifically looking at red-green color blindness. Red-green color blindness is an X linked recessive disorder. Having an XB means that the individual will have normal vision and will not be color blind with this allele. However, it's the Xb that leads to having this particular color blindness. Because it is an X linked recessive disorder, females are going to need to have two Xbs in order to be affected, whereas males only need one Xb to be affected. The affected individuals are the ones that have the filled-in black boxes. You'll notice that all of the individuals with a filled-in black box have X chromosomes only with the recessive allele. Notice that there is a large tendency for males to be affected more than females, and the vast majority of the people affected in this case are males. There's only one female that is affected in this scenario, and that is a pattern that will help you identify X linked recessive disorders much more quickly, just by looking to see if more males are significantly affected than females.
Notice again that a female can only be affected if the father is affected and the mother is at least a carrier. When we look at the affected female, we see that the father is affected, and the mother is a carrier, meaning that she is heterozygous. That's the only way a female can be affected. All the sons of an affected female are going to be affected. Notice that the only son of this couple is affected because the mother is affected.
This concludes our introduction to X linked recessive pedigrees, and the biggest takeaway should be that more males are going to be affected than females, which is a big clue that can help you identify X linked recessive pedigrees more quickly. This here concludes this lesson, and I'll see you all in our next video.