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
-
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:
given
see the image
Please Rate My Answer..........Thank...........u...
Get Answers For Free
Most questions answered within 1 hours.