A genetic pedigree showing that only males are affected by a certain disorder is evidence of Y-linked inheritance or possibly X-linked recessive inheritance , but the key distinction lies in the pattern of transmission:
- Y-linked inheritance : Since only males have a Y chromosome, disorders caused by mutations on the Y chromosome affect only males and are passed strictly from father to son. All sons of an affected male will inherit the disorder because they receive their Y chromosome from their father
- X-linked recessive inheritance : Males are more commonly affected because they have only one X chromosome. A single recessive mutation on the X chromosome causes the disorder in males, while females (with two X chromosomes) are usually carriers and rarely affected. In this pattern, affected males do not pass the disorder to their sons (because sons inherit the Y chromosome from their father), but can pass the mutated X chromosome to all daughters, who become carriers. Sons of carrier females have a 50% chance of being affected
If the pedigree shows that only males are affected and the disorder is passed from father to all sons , this is characteristic of Y-linked inheritance. If the disorder affects only males but is inherited through carrier females and shows no male-to-male transmission, it is X-linked recessive.
Summary Table
Inheritance Type| Affected Individuals| Transmission Pattern| Key Feature
---|---|---|---
Y-linked| Only males| Father to all sons| No females affected; all sons
affected
X-linked recessive| Mostly males| Carrier females to affected sons; no male-
to-male transmission| Males affected; females usually carriers
Thus, a pedigree showing only males affected by a disorder is most directly evidence of Y-linked inheritance if the disorder passes father to son, or X-linked recessive inheritance if it passes through carrier females and affects males predominantly
