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Ichthyosis is a rare X-linked recessive disorder that is characterized by scaling of the skin around the neck and lower extremities. A young couple, Bart and Jenny, are expecting a child and are aware there might be a chance that their child could be affected by this disorder. Jenny (the wife) has ichthyosis, but Bart (her husband) is unaffected and completely normal with respect to the allele responsible for this disorder.
Both Bart and Jenny were Biology majors as undergraduates. Knowing a little about the pattern of X-linked recessive inheritance, Bart and Jenny were concerned when ultrasound revealed that they would be having a son. However, genetic testing performed on the baby shortly after birth revealed that their newborn son, Mark, did not have ichthyosis. If non-disjunction occurred, assume it happened in only one of the two parents, and during only one of the two meiotic divisions.
Let’s assume that non-disjunction of the sex chromosomes occurred during only one meiotic division, and in only one of Baby Mark’s two parents. This non-disjunction event led to the production of the gamete that was partially responsible for Baby Mark’s unusual combination of genetic conditions.
Clearly Draw a diagram showing the non-disjunction event that produced the gamete that led to Baby Mark’s conception. Be sure to include all of the following in your answer:
(1) Indicate which parent experienced non-disjunction.
(2) Label ALL chromosomes, chromatids, AND GENES.
(3) Clearly indicate the specific meiotic division during which non-disjunction occurred.
(4) Show ALL of the products of meiosis produced by the parent who experienced non-disjunction.
(5) Indicate which gamete led to the conception of the baby son, Mark, who did not have ichthyosis.
(6) Indicate which chromosomes and genes were present in the gamete contributed by the other parent.
(7) Indicate the specific genes and chromosomes present in Baby Mark.
You may assume that ONLY ONE PARENT EXPERIENCED NON-DISJUNCTION and that non-disjunction occurred during only ONE meiotic division.
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Which gamete led to baby Mark's conception? Could you indicate which circle is showing this?
Which gamete led to baby Mark's conception? Could you indicate which circle is showing this?
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