Rafic Hariri High School

Life Sciences (LS) Section | Grade 12

First Semester Examination

Biology Exam

Subject: Human Genetics

Name: __________________________ Duration: 50 Minutes

First Exercise: Duchenne Muscular Dystrophy (5 points)

Duchenne Muscular Dystrophy (DMD) is a severe type of muscular dystrophy characterized by rapid progression of muscle degeneration, eventually leading to loss of ambulation and respiratory difficulties. This genetic disorder is caused by a mutation in the DMD gene, which provides instructions for making a protein called dystrophin. This protein acts as an anchor, connecting the cytoskeleton of a muscle fiber to the surrounding extracellular matrix.

  1. Pick out from the text the biological role of the protein dystrophin.

    2. Document 1 presents the pedigree of a family where several individuals are affected by Duchenne Muscular Dystrophy.

    Document 1: Pedigree of the Affected Family

    I 1 2 II 1 2 3 4 III 1 Healthy Male Affected Male Healthy Female
  2. Specify if the allele responsible for Duchenne Muscular Dystrophy is dominant or recessive. Justify your answer.
  3. Does the distribution of affected individuals in Document 1 suggest an autosomal or a sex-linked chromosomal location? Provide two arguments based on the pedigree to support your answer.
  4. Using the symbols (D or d) for the alleles, determine the genotypes of the following individuals:

    Individual I-2:

    Individual II-2:

  5. Could individual II-3 give birth to an affected daughter? Justify by referring to the necessary genotype of the father.

End of Examination

Scientific thinking leads to discovery.