If a genetic counselor was examining a pedigree chart and noticed an occurrence of a disease in every generation, the counselor would most likely assume that the disease was caused by:

• A. A new reoccurring mutation.
• B. An autosomal recessive disorder.
• C. A chromosomal abnormality.
• D. An autosomal dominant disorder.
• E. Having an extra set of chromosomes.

Answer: (D)

Verified step by step guidance

1. Examine the pattern of inheritance in the pedigree chart. If the disease appears in every generation, it suggests a dominant pattern of inheritance.
2. Consider the possibility of a new reoccurring mutation. However, this is less likely if the disease consistently appears in every generation, as new mutations would not typically show such a pattern.
3. Evaluate the likelihood of an autosomal recessive disorder. Such disorders usually skip generations, as two copies of the recessive allele are needed for the disease to manifest.
4. Assess the possibility of a chromosomal abnormality. While these can cause diseases, they often result in more sporadic occurrences rather than a consistent generational pattern.
5. Conclude that the most likely cause of the disease appearing in every generation is an autosomal dominant disorder, where only one copy of the dominant allele is needed for the disease to be expressed.