Problem 20 - Biochemistry

Question

Duchenne muscular dystrophy is a sex-linked recessive disorder associated with severe deterioration of muscle tissue. The gene for the disease: a. is inherited by males from their mothers. b. should be more common in females than in males. c. both a and b. d. neither a nor b.

Step-by-Step Solution

Answer

The correct answer is 'a', the gene for Duchenne muscular dystrophy is inherited by males from their mothers.

Step 1: Understanding Duchenne muscular dystrophy and inheritance patterns.

Duchenne muscular dystrophy is a sex-linked recessive disorder, which means the gene for the disorder is located on the X chromosome. Males have one X and one Y chromosome (XY), and females have two X chromosomes (XX). So, a male who inherits an affected X chromosome from his mother will display the disorder. In females, the presence of another (normal) X chromosome usually prevents the development of the disease itself. Females can be carriers and can pass on the affected X chromosome to their offspring.

Step 2: Comparing the statements with the facts.

Now, let's evaluate the given options: 'a' states that the gene is inherited by males from their mothers, which is true as per the explanation provided in step 1. 'b' claims that the disorder should be more common in females, which is incorrect as males are more commonly affected, as they only have one X chromosome, and thus if it carries the disorder, they will exhibit symptoms.

Step 3: Conclusion

Based on the comparison made in step 2, it can be concluded that statement a is true and b is false. Thus, the correct option is 'a'.

Key Concepts

Sex-Linked Recessive Disorder

When we refer to a 'sex-linked recessive disorder' like Duchenne muscular dystrophy (DMD), we’re discussing a genetic condition that is passed down through the X chromosome, one of the two sex chromosomes (X and Y). Since males have only one X chromosome inherited from their mother and one Y chromosome from their father, they are more likely to express the symptoms of a recessive gene on the X chromosome.

In the case of DMD, the gene that causes the disorder is present on the X chromosome, and because males have just one X, inheriting a defective gene will result in the condition manifesting. In contrast, females have two X chromosomes. This means that even if one X chromosome carries the recessive gene, the second one often helps compensate, preventing the disorder from developing. However, females can still be carriers and may pass the affected gene to their children.

Muscle Tissue Deterioration

Duchenne muscular dystrophy is characterized by progressive muscle tissue deterioration over time. This condition affects the dystrophin protein, which is critical for maintaining the integrity of muscle fibers. The absence or reduced levels of dystrophin lead to damage and weakening of muscles, which can impact mobility and various bodily functions. Muscle deterioration in Duchenne muscular dystrophy starts in early childhood and progressively gets worse.

This is why individuals with DMD often experience difficulty with walking, standing, and eventually breathing as the respiratory muscles weaken. It is important to understand not just the genetic basis of the condition, but also its impact on the patient's quality of life and the challenges involved in daily activities.

Genetics and Inheritance Patterns

When exploring genetics and inheritance patterns, it is essential to detail how genetic diseases like DMD are passed from parents to offspring. Duchenne muscular dystrophy follows an X-linked recessive inheritance pattern, as previously mentioned. If a mother is a carrier of the defective dystrophin gene on one of her X chromosomes, each son has a 50% chance of inheriting the disorder, and each daughter has a 50% chance of being a carrier.

Daughters who inherit the affected X from their father, who will have the disorder, will be carriers as well. Understanding these patterns is crucial for genetic counseling and for families to assess the risk of having children with such conditions. As genetic testing becomes more commonplace, being informed about these inheritance patterns empowers individuals and families to make informed decisions about their health and their children's health in the context of genetic disorders.