Question

Which of these factors provides evidence that the disorder may have a genetic cause?

A. An increased frequency of the disorder in blood relatives of an affected individual than in the general population.
B. It is found more commonly in both fraternal twins than in both identical twins.
C. Individuals that live with an affected individual are more likely to also exhibit the disorder.
D. Two of the above
E. All of the above

Answer 1

Factor A, which points to an increased frequency of the disorder in blood relatives, provides evidence of a genetic cause for a disorder. The difficulty in pinpointing the cause of nervous system disorders stems from unknown genes, variable symptom presentation, and complex inheritance patterns. Pedigree analysis is a crucial tool for studying the genetic inheritance of disorders.

Step-by-step explanation:

The question seeks to identify factors that suggest a genetic cause for a disorder. One significant factor is A. An increased frequency of the disorder in blood relatives of an affected individual than in the general population. This is due to the shared genetic material among relatives which may contain the genes responsible for the disorder, pointing to a genetic inheritance pattern.

Option B, which suggests the disorder is found more commonly in fraternal twins than in identical twins, does not support a genetic cause since identical twins share more genetic material than fraternal twins, and would therefore have a higher incidence of the disorder if it were genetic. Option C refers to environmental or contagious factors rather than genetic inheritance.

The difficulty in identifying the cause of nervous system disorders lies in several factors (all of the above from option 22d), including the unknown genes associated with the diseases and the variability in symptom onset and display. Moreover, modes of inheritance such as when both male and female offspring have similar chances of inhering a disease or when specific alleles are involved in disease manifestation further complicate understanding the genetic bases for these conditions.

Genetic disorders can be passed down from parents to their children via various inheritance patterns. The transmission depends on the type of genetic defect involved, such as recessive or dominant alleles, and chromosomal abnormalities. In some cases, the inheritance can be complex and influenced by multiple genetic and environmental factors, which is why pedigree analysis, instead of direct genetic testing, often proves useful in understanding these patterns.

It is also important to note that genetic disorders can maintain themselves in a population at low levels until factors like inbreeding increase the likelihood of diseased offspring. As such, genetic counseling and analysis offer useful insights into the risks of inheriting or passing on genetic disorders.