Question

Which genetic phenomenon would make it difficult to determine the mode of inheritance from analysis of a pedigree?

a)With X-linked dominant inheritance, affected males can't have affected sons if their mates are normal.
b)With autosomal recessive inheritance, affected children often have phenotypically normal parents.
c)Males with a mitochondrial disorder do not pass it on to their children.
d)Incomplete penetrance occurs with some genotypes.
e)Only half the children will be likely be affected with an autosomal dominant trait if one of the parents is affected.

Answer 1

Incomplete penetrance is the genetic phenomenon that complicates determining the mode of inheritance in pedigree analysis because not all individuals with a dominant allele will express the phenotype, making the inheritance pattern unclear.

Step-by-step explanation:

The genetic phenomenon that would make it difficult to determine the mode of inheritance from analysis of a pedigree is incomplete penetrance. When a genotype does not always produce the corresponding phenotype, this is known as incomplete penetrance. With this phenomenon, not all individuals with a dominant allele will express the trait, which can obscure patterns of inheritance in a pedigree chart. For autosomal or X-linked dominant traits, it may seem like the affected genotype is skipping generations, challenging the ability to discern the mode of inheritance accurately.

For context, X-linked recessive inheritance occurs when a trait is determined by an allele on the X chromosome. Males (XY) who inherit the affected X chromosome will express the trait because they don't have a second X chromosome to mask the effect of the recessive allele. Females (XX) must inherit two affected X chromosomes—one from each parent—to express the trait fully. If they inherit only one such X, they become carriers without necessarily showing symptoms of the condition.

X-linked dominant inheritance patterns are also complex, where affected males pass the trait to all daughters but no sons. An affected female has a 50% chance of passing the trait onto each child, regardless of gender. This pattern can resemble autosomal dominant inheritance when examining a pedigree.