Problem 28 - Anatomy and Physiology of Animals

Question

Marfan syndrome is inherited in an autosomal dominant pattern. Which of the following is true? a. Female offspring are more likely to be carriers of the disease. b. Male offspring are more likely to inherit the disease. C. Male and female offspring have the same likelihood of inheriting the disease. d. Female offspring are more likely to inherit the disease.

Step-by-Step Solution

Answer

Option C is correct: Male and female offspring have the same likelihood of inheriting the disease.

Step 1: Understanding Autosomal Dominant Inheritance

Marfan syndrome is inherited in an autosomal dominant manner, which means the defective gene responsible for the disorder is located on one of the autosomes (non-sex chromosomes). This also means that only one copy of the defective gene, inherited from either parent, is sufficient to cause the disorder.

Step 2: Equal Likelihood for Both Sexes

Because the disease is autosomal, it does not depend on sex chromosomes like X or Y. Thus, autosomal diseases affect males and females equally. Each child, regardless of gender, has a 50% chance of inheriting the defective gene from an affected parent.

Step 3: Eliminate Incorrect Options

Given the nature of autosomal dominant inheritance, options a, b, and d are incorrect because they suggest gender influences the likelihood of inheriting the disease. In autosomal dominant patterns, neither male nor female offspring are more likely to inherit the condition.

Step 4: Conclusion

Since the inheritance pattern is independent of gender, the correct statement is option C: 'Male and female offspring have the same likelihood of inheriting the disease.'

Key Concepts

Marfan syndrome

Marfan syndrome is a genetic disorder that affects the body's connective tissue. This condition is caused by a mutation in the FBN1 gene, which leads to problems in the protein called fibrillin-1. This protein plays a crucial role in maintaining the elasticity and strength of connective tissues found throughout the body. As a result, individuals with Marfan syndrome may experience issues with their heart, blood vessels, bones, joints, and eyes.

People with Marfan syndrome often exhibit distinct physical features, such as long arms and legs, a tall and thin body frame, and flexible joints. The severity of symptoms can vary significantly, even among family members. Some people may have mild symptoms, while others may encounter more serious complications like heart valve abnormalities.

• Heart and blood vessel problems, including aortic enlargement
• Vision problems due to lens dislocation
• Muscle and joint pain

Early diagnosis and treatment are essential in managing Marfan syndrome effectively, as interventions can help prevent or reduce certain complications. Regular monitoring and management by a multidisciplinary team, including cardiologists and orthopedists, can improve the quality of life for those affected by this condition.

Genetic inheritance patterns

Genetic inheritance patterns refer to how specific traits or disorders are transmitted from parents to their offspring through genes. Inheritance patterns can be broadly classified into several types, each determined by the gene's location and the number of gene copies needed to express a trait. The most common patterns include:

• Autosomal Dominant: Only one copy of a faulty or mutated gene, located on a non-sex chromosome (autosome), is necessary for the expression of the disorder. An affected individual has a 50% chance of passing the defective gene to each child.
• Autosomal Recessive: Two copies of a mutated gene are required for the disease to manifest. Individuals with only one copy of the mutant gene are carriers and typically do not show symptoms.
• X-linked: Disorders are caused by mutations in genes on the X chromosome. These may affect males more frequently, as they have only one X chromosome.

Recognizing the inheritance pattern of a disorder helps predict its transmission to future generations and aids in genetic counseling and preventive strategies.

Autosomal disorders

Autosomal disorders are genetic conditions linked to genes located on the autosomes. These chromosomes are numbered 1 to 22, and autosomal disorders can arise from mutations in any of these chromosomes. They are distinct from disorders linked to sex chromosomes (X and Y).

• Autosomal Dominant Disorders: Examples include Marfan syndrome, Huntington's disease, and familial hypercholesterolemia. These require only one mutated gene copy to cause the disorder, meaning the condition often appears in every generation.
• Autosomal Recessive Disorders: Common conditions of this type include cystic fibrosis, sickle cell anemia, and Tay-Sachs disease. Both parents must carry and pass on the mutated gene for the disease to manifest in their offspring.

Autosomal disorders can affect various body systems depending on the gene involved. Some might only show physical signs, while others can affect organ function. Accurate medical diagnosis and understanding the mutation type greatly assist in treatment planning and family counseling.