A woman affected with an X-linked recessive disorder:

The answer to question 1  ANS: C
An X-linked recessive disorder means that in a woman, both X chromosomes must have the mutation if she is to be affected. Because males have only one copy of the X chromosome, they will be affected if their X chromosome carries the mutation.

The answer to question 2  ANS: D
A man with an X-linked dominant disorder will transmit the mutation to 100 of his daughters (they receive his X chromosome) and none of his sons (they receive his Y chromosome). The pedigree of a family with an X-linked dominant disorder would reveal all the daughters and none of the sons affected with the disorder if the father has an X-linked disorder.

The answer to question 3  ANS: A
An individual with an abnormal number of chromosomes has a condition called aneuploidy, which is frequently associated with mental problems or physical problems or both (Jorde, Carey, & Bamshad 2010; Nussbaum et al. 2007).

The answer to question 4  ANS: B
Everyone born with an X-linked dominant disorder will be affected with the disease. Transmission of the disorder to the next generation varies by gender, however. A woman will transmit the mutation to 50 of all her offspring (male or female).

The answer to question 5  ANS: A
It is important that parents understand that if they both carry a mutation, the risk to each of their offspring (each pregnancy) is an independent event: 25 disease free, 25 affected, and 50 carrier.

The answer to question 6  ANS: D
Individuals who have an AR disorder have two mutated genes, one on each allele of the chromosome. Parents of an affected person are called carriers because each parent carries one copy of the mutation on one chromosome and a normal gene on the other chromosome. Carriers typically are not affected by the disease. In pedigrees with an AR inheritance patterns, males and females will be equally affected because the gene mutation is on an autosome.

The answer to question 7  ANS: C
In autosomal recessive (AR) disorders, the offspring inherits the condition by receiving one copy of the gene mutation from each of the parents. Autosomal recessive disorders must be inherited through both parents (Nussbaum et al. 2007). Individuals who have an AR disorder have two mutated genes, one on each locus of the chromosome. Parents of an affected person are called carriers because each carries one copy of the mutation on one chromosome and a normal gene on the other chromosome. Carriers typically are not affected by the disease.

The answer to question 8  ANS: A
Pedigrees associated with autosomal dominant (AD) disorders typically reveal multiple affected family members with the disease or syndrome. When analyzing the pedigree for AD disorders or syndromes, it is common to see a vertical pattern denoting several generations of affected members.

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