User:Ezra Smith/X-linked recessive inheritance

https://www.scielo.br/scielo.php?script=sci_arttext&pid=S0004-282X2012000700001 good discussion on how X-linked traits can't be defined as recessive or dominant. Not a primary source but a good branching point for more research.

Changes to the "Sex differences in phenotype/genotypes and frequency" Section:


 * Change title of Section to: Patterns of Inheritance"
 * Move final paragraph of this section to a new section called: Push back on Recessive/Dominant Terminology
 * Rewrite both sections

Patterns of Inheritance
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. 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. 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. 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.

Push Back on Recessive/Dominant Terminology
A few scholars have suggested discontinuing the use of the terms dominant and recessive when referring to X-linked inheritance. The possession of two X chromosomes in females leads to dosage issues which are alleviated by X-inactivation. Stating that the highly variable penetrance of X-linked traits in females as a result of mechanisms such as skewed X-inactivation or somatic mosaicism is difficult to reconcile with standard definitions of dominance and recessiveness, scholars have suggested referring to traits on the x chromosome simply as X-Linked.