Question

Part II – Genetic Basis of the Disorder

As Alexander’s family and you have now discovered, spondyloepiphyseal dysplasia congenita (SEDC) is a genetic

disorder in which the primary deficits are abnormal growth of one or more spinal vertebrae and the growing ends of

the femurs, resulting in disproportionate, short-trunk dwarfism (Parikh & Crawford, 2017). Interestingly, both of

Alexander’s parents, his grandparents and an older sister are of normal height. Therefore, what do you think the mode

of inheritance is for SEDC?

Let’s make a couple assumptions at this time. First, assume that a mutation in a single gene is responsible for Alex

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ander’s condition. Second, assume that the affected gene is on an autosome (non-sex chromosome). Do you think

that the mutant allele that has caused Alexander’s condition is dominant or recessive to the normal (wild-type) allele

for this gene? Test these two alternative hypotheses by drawing two copies of a small family pedigree according to the

questions below that includes Alexander, his sister and each of his parents.

Questions

1.

For one pedigree, draw the symbols and add the likely genotypes of Alexander, his sister and each of his parents,

as if SEDC is an autosomal

dominant

condition. Use the letters “D” and “d” to represent the dominant and

recessive alleles, respectively, for the affected gene.

2.

For the second pedigree, draw the symbols and add the likely genotypes of Alexander, his sister and each of his

parents, as if SEDC is an autosomal

recessive

condition. Use the letters “D” and “d” to represent the dominant

and recessive alleles, respectively, for the affected gene.

3.

Which hypothesis do you think is supported by Alexander’s family pedigree?

As you will soon learn, SEDC is actually an autosomal dominant disorder. Given that both of Alexander’s parents

are normal height (i.e., neither has SEDC), how is it possible that Alexander came to have an autosomal

dominant

disorder? This is a question that Alexander’s father has also wondered about.

Question

4.

How would you explain this to Alexander’s father? In other words, what are some possible causes of a new

mutation, and when and where (i.e., in what cell type) might Alexander’s SEDC mutation have appeared?

Brainstorm possible answers to these questions and list some possibilities.

I only need number 4

Answer 1

Answer:

given see the image

• LHS of image show: Autosomal dominant pattern
• RHS of image show: Autosomal recessive pattern
• Most appropriate will be Autosomal recessive pattern.
• As, Autosomal dominant pattern is not fit model as one of the Alexander parent must have SEDC
• Since, Dd outcome is only possible if one of parent is DD or Dd.

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