Final answer:
HD, or Huntington's Disease, can develop in a child even if the parents are unaffected but are carriers of the disease. Each with one normal and one mutated allele, they have a 50% chance of passing the dominant HD allele to their offspring. A Punnett square exemplifies how the disorder can be transmitted despite parents being clinically unaffected.
Step-by-step explanation:
HD, which stands for Huntington's Disease, can develop in a child born of unaffected parents if both parents are carriers of the disease. This scenario implies that each parent has one normal allele (A) and one mutated allele (H), hence they are heterozygous (Ah) for the condition. Huntington's Disease is an autosomal dominant disorder, meaning that having just one mutated gene (H) is enough to develop the disease. If HD appears in an offspring of parents who do not show symptoms, it indicates that both parents are heterozygous carriers and they likely have the genotype Ah.
The risk of transmitting the disease to their children can be calculated using a Punnett square. Each child has a 50 percent chance of inheriting the affected gene (H) and therefore a chance of developing the disease. However, it is crucial to note that the onset of symptoms usually does not occur until middle age, which might be after the affected individuals have already had children of their own.
Additionally, other genetic conditions may follow different inheritance patterns. For example, color blindness is an X-linked recessive trait, indicating that an unaffected mother who is a carrier of the allele (XcX) can pass the condition to her sons. This shows the varying complexities in genetic inheritance.
Lastly, while HD is typically inherited, new mutations can also occur spontaneously; this is however, very rare. Understanding genetic inheritance and the relationship between carriers and their offspring is important for determining the risk of inheriting such conditions.