Questions: Which mode of inheritance is characterized by the presence of affected individuals in every generation? Autosomal dominant (AD) Autosomal recessive (AR) X-linked recessive (XR) X-linked dominant (XD)

The answer is the first one (Autosomal dominant, AD): the presence of affected individuals in every generation.

Explanation for each option:

1. Autosomal dominant (AD): This mode of inheritance is characterized by the presence of affected individuals in every generation. This is because only one copy of the mutated gene, inherited from an affected parent, is sufficient to cause the disorder. Therefore, the trait tends to appear in every generation, and affected individuals have a 50% chance of passing the trait to their offspring.

2. Autosomal recessive (AR): In this mode, two copies of the mutated gene are necessary for an individual to be affected. As a result, the trait may skip generations, as carriers (individuals with only one copy of the mutated gene) do not show symptoms.

3. X-linked recessive (XR): This mode of inheritance often affects males more frequently than females, as males have only one X chromosome. Affected males can pass the gene to all their daughters (who become carriers) but not to their sons. The trait can skip generations, especially if carrier females do not have affected sons.

4. X-linked dominant (XD): This mode can also show affected individuals in every generation, but it is less common than autosomal dominant inheritance. Both males and females can be affected, but affected males will pass the trait to all their daughters and none of their sons.

In summary, the autosomal dominant mode of inheritance is most commonly associated with the presence of affected individuals in every generation.