Review Question - QID 880

The pedigree chart (males are squares and females are circles) shown in Figure A demonstrates an autosomal recessive trait.

Diastrophic dysplasia is the only autosomal recessive condition with all of the other options being X-linked recessive disorders. Along with Becker's MD these are the main orthopaedic X-linked recessive disorders.

There are many more autosomal recessive orthopedic disorders. Autosomal recessive pedigrees often appear in both sexes with equal frequency, tend to skip generations, and affected offspring are usually born to unaffected parents. When both parents are heterozygote, approximately 1/4 of the progeny will be affected.

X-linked and autosomal dominant disorders with complete penetrance will not skip generations.

X-linked recessive disorders will have affected sons if the mother has the disease (this does not occur in the 3rd cross of Figure A on the far right).