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== Patterns of Inheritance ==
[[File:Haemophilia family tree.GIF|thumb|Patterns of X-Linked Recessive Inheritance in the Royal Family]]
In humans, inheritance of X-linked recessive traits follows a unique pattern made up of three points. The first is that affected fathers cannot pass x-linked recessive traits to their sons because fathers give Y chromosomes to their sons. This means that males affected by an x-linked recessive disorder inherited the responsible X chromosome from their mothers. Second, x-linked recessive traits are more commonly expressed in males than females.<ref>{{Cite web|last=|first=|date=8 July 2009|title=Understanding Genetics: A New York, Mid-Atlantic Guide for Patients and Health Professionals|url=https://www.ncbi.nlm.nih.gov/books/NBK115561/|url-status=live|archive-url=|archive-date=|access-date=9 June 2020|website=National Center for Biotechnology Information}}</ref> This is due to the fact that males only possess a single X chromosome, and thus only require one mutated X in order to be affected. Women posses two X chromosomes, and thus must receive two of the mutated recessive X chromosomes (one from each parent). A popular example showing this pattern of inheritance is that of the descendants of Queen Victoria and the blood disease hemophilia.<ref>{{Cite web|date=2014-03-04|title=History of Bleeding Disorders|url=https://www.hemophilia.org/Bleeding-Disorders/History-of-Bleeding-Disorders|access-date=2020-06-09|website=National Hemophilia Foundation|language=en}}</ref> The last pattern seen is that x-linked recessive traits tend to skip generations, meaning an affected grandfather will not have an affected son, but could have an affected grandson through his granddaughter.<ref>{{Cite book|last=Pierce|first=Benjamin A.|title=Genetics: A Conceptual Approach|publisher=Macmillan Learning|year=2020|isbn=978-1-319-29714-5|pages=154–155}}</ref> Explained further, all daughters of an affected man will obtain his mutated X, and will then be either carriers or affected themselves depending on the mother. The resulting sons will either have a 50% chance of being affected (mother is carrier), or 100% chance (mother is affected). It is because of these percentages that we see males more commonly affected than females.
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