A 42 year old mother has two different alleles for the X chromosome, A1 and A2; the father’s X has allele A3.
A) (3 point) Their son is found to have a single bar body in the nucleus of his cells. He was genetically tested and found to have both the A1 allele and the A3 allele. Describe in detail the defect in meiosis that would make this possible. A narrative or a diagram is an acceptable answer.
B) (2 point) Their doctor was surprised that the A3 allele is found in the son’s cells, why would this be the case?
C) (2 point) What genotype/s was the doctor expecting to find based on his knowledge of when non-disjunction is most common? A narrative or a diagram is an acceptable answer.
D) (2 point) Extra or fewer chromosomes are one of the more common abnormalities that are observed in a fetus, but most of them are not viable or lead to a still born child. This child is healthy and relatively normal. Why, in this case, is the extra dose of genes less of a problem for the child’s health?
E) (1 point) An extreme example of aneuploidy is XXXXY. How many Barr bodies would be present in the cells of this person?
F) (2 points) What series of non-disjunction events could explain the existence of an XXXXY individual?
G) (2point) What series of non-disjunction events could explain the existence of an XXXX individual?
H) (1point) The XXXXY phenotype is much more severe than for XXY, despite the fact they have the same number of X chromosomes that express normally. What is the cause of the more severe phenotype that is seen?