Genetic Causes and Inheritance of Achondroplasia

• Cause: Achondroplasia is caused by a mutation of the fibroblast growth factor receptor 3 gene. This gene's loci is the 4th chromosome. This gene controls the growth rate of long bones like the humerus and the femur. However, when a mutation occurs, the ability of the bone to grow becomes extremely limited. Instead of producing the correct amino acid, it produces another. ^[1]

FGF signalling in the growth plate.

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• Inheritence: Achondroplasia is inherited as an autosomal dominant trait. Autosomal dominant traits are linked to non-sex chromosomes. Eighty percent of achondroplasia cases result from new genetic mutations, not from the transmission of defective genes from parent to offspring. However, people with achondroplasia are very likely to pass it on to their children, as seen in the Punnet squares below.

When only one parent has the gene and the other parent doesn't:

When both parents have the the gene:

Sources:

"achondroplasia." Encyclopædia Britannica. 2009. Encyclopædia Britannica Online. 27 Oct. 2009 <http://www.britannica.com/EBchecked/topic/3635/achondroplasia>.