Physiological Adaptation Q 56
Which statement made by the nurse describes the inheritance pattern of autosomal recessive disorders?
A. An affected newborn has unaffected parents.
B. An affected newborn has one affected parent.
C. Affected parents have a one in four chance of passing on the defective gene.
D. Affected parents have unaffected children who are carriers.
Correct Answer: C. Affected parents have a one in four chance of passing on the defective gene.
Autosomal recessive disorders can be passed from the parents to the infant. If both parents pass the trait, the child will get two abnormal genes and the disease results. Parents can also pass the trait to the infant. Patients affected with autosomal recessive (AR) diseases have a disease allele on each chromosome. The pattern of individuals affected with an AR disease can be traced through a family to determine which individuals are carriers and which individuals are likely to become impacted.
Option A: To have an affected newborn, the parents must be carriers. The easiest way to determine the inheritance pattern of a disorder in a family is by looking at a pedigree. Autosomal recessive diseases typically affect both females and males equally. Autosomal recessive patterns manifest by skipping generations as the affected are usually children of unaffected carriers.
Option B: Both parents must be carriers. The most common situation of an autosomal recessive disease occurs when the parents are each carrier or heterozygous (Dd). Children of carrier parents have a 25% chance of inheriting the disorder. This value is obtained by using the Punnett square model used in genetics.
Option D: The parents might have affected children. Each parent has a 50% chance of passing on the disease allele. Using the multiplication rule of probability, there is a 50% chance that the father passes on his disease allele and a 50% chance that the mother passes on her disease allele; 50% x 50% = 25%. So with the mating of carrier parents, there is a 25% chance that the child will be affected, a 50% chance that the child would be a carrier, and 25% chance that they would be homozygous dominant and unaffected.