1. A Rh negative woman gives birth to her first child who is Rh positive with no
ID: 10331 • Letter: 1
Question
1. A Rh negative woman gives birth to her first child who is Rh positive with no complications. When she becomes pregnant with her second child, her doctor gives her an injection of Rh immunoglobulin (RhIg).a.Why did her doctor inject her with RhIg?
b.Why did she receive RhIg for the second pregnancy but not the first?
2. During a biology lab activity the class is asked to look for Barr bodies in their cells. David, a male class member, identifies Barr bodies in his cells.
a.What is David’s likely genotype?
b.What mechanism causes this condition?
3. A scientist has cloned a calico cat, but the clone’s coat pattern looks nothing like the original cat’s coat even though they share identical DNA and were raised in identical environmental conditions. Knowing that the gene for coat color is on the X chromosome, explain why these two genetically identical cats do not share the same phenotype.
4.The allele for a Widow’s peak hairline is dominant over the allele for a straight hairline. Based on this information it can be assumed:
a.A Widow’s peak hairline would be more present (higher frequency) in any human population
b.A Widow’s peak hairline is the “wildtype” hairline c. A Widow’s peak hairline is due to a mutation in the hairline gene d. None of the above can be assumed about a dominant allele
Explanation / Answer
Not sure of 1, but here's what I can get: 2) a)Barr bodies are random X chromosome inactivation. Females have this, as two XX are not needed for DNA and one is randomly inactivated in each cell. For David, a male and XY, to have barr bodies indicates he must have two X chromosomes in addition to his Y. b) XXY is caused by nondisjunction in meiosis (XY are sex chromosomes!). It's up to you to discern whether it's from MI or MII :) 3)Calico cats are always female, hence, they're fur is covered in different colored patches. This is again due to Barr Bodies and X chromosome inactivation. Because an X is randomly inactivated in each cell, this means not all cells express the same X chromosome (The cell chooses one to inactivate, but not all cells choose the same one). There is no way to determine which X chromosome will be inactivated nor is it predetermined in the DNA - because of this, no two calico cats, no matter how genetically identical, will look alike. 4) I'm pretty sure this is correct: D) None of the above can be assumed a) even though it is a dominant trait, not every human population would express it in a higher frequency. Some populations have a high frequency of recessive traits (blond hair, blue eyes), while other have a high frequency of dominant traits (dark hair, dark eyes) b) "wild-type" implies the norm, but again, this is not always so c) It is stated that it is dominant, meaning it follows Medelian genetics and is not a mutation
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