Myotonic dystrophy is a progressive genetic disorder that affects muscle function, causing muscle wasting, prolonged muscle tensing (myotonia), and cataracts. Symptoms typically do not become apparent until adulthood, usually when an individual is between 20 and 40 years of age.
The condition is inherited and is caused by a dominant allele (MMM) and not the recessive allele (mmm).
A heterozygous male mates with a homozygous recessive female.
Use a genetic diagram to show the parental genotypes, the gametes produced, and the possible genotypes and phenotypes of the offspring.
Explain why it is difficult for a doctor to decide if an asymptomatic 12-year-old has the condition based solely on physical symptoms.
Suggest what other information or methods the doctor could use to determine if the 12-year-old will develop the disease.
Many other genetic disorders, such as phenylketonuria (PKU), are caused by recessive alleles rather than dominant alleles.
Explain how examining a family pedigree diagram would enable you to determine if a condition is caused by a recessive allele.
