How many defective copies of a gene must someone inherit to express a disease caused by a dominant gene? How many defective copies of a gene must someone inherit to express a recessive disorder? What is the expected phenotypic ratio of affected to unaffected individuals for a dominant disorder? Solution In autosomal dominant inheritance even single copy of gene requires to get expressed phenotypically in offspring In autosomal recessive inheritance two copies of allele of the disease are require for an individual to the susceptible to express phenotypically There is 50% chances of offspring to get affected in a dominant disorder.