Lecture 35: Aneuploidy II: Translocation, Human Aneuplodies, Imprinting
1. Human autosomal aneuploidies tend to cause very severe symptoms.
a. What mechanisms are responsible for the generally more severe effects of autosomal aneuploidies than are seen with sex chromosome aneuploidies.2. Briefly identify the genetic defect that is responsible for cri-du-chat syndrome.
b. What is the only human autosomal trisomy that is likely to allow survival into adulthood.
c. Identify two othe human autosomal trisomies that sometimes result in live births, but with severe birth defects.
d. Identify three different human sex chromosome trisomies that are viable to adulthood.
e. Identify a human monosomy that is viable to adulthood.
3. Define the following terms
a. Robertsonian translocation
b. Imprinting
c. Reciprocal translocation
d. Translocation heterozygote
e. Alternate segregation (of reciprocal translocation)
4. Explain how a translocation can cause Down syndrome.
5. What mechanism has been proposed to account for the fact that humans have 46 chromosomes while the great apes have 48? What observations support the proposed mechanism?
6. Describe two distinctly different ways that Down syndrome can originate in humans. What genetic similarity is shared in the two cases? How do they differ?
7. Distinguish between maternal imprinting and paternal imprinting in a manner that makes it clear that you understand what each is and how they differ.
8. What is the result of replacing the male pronucleus in a newly fertilized mouse egg with a second female pronucleus. What explanation is offered for the phenomenon that is observed? What name is applied to a zygote that has been manipulated in this manner?
9. Same as question 3 except that the female pronucleus is replaced with a second male pronucleus.
10. How has the IGF2 gene been used to study genetic imprinting? Why is this gene particularly valuable for such studies?
11. What phenotype would you expect from each of the following
genotypes.
IGF2- = loss of function mutation of the IGF2 gene;
IGF2+ = wild type allele of IGF2 gene.
a. Maternal IGF2-, paternal IGF2+
b. Paternal IGF2-, maternal IGF2+
c. Paternal IGF2-, maternal IGF2-
d. Paternal IGF2+, maternal IGF2+
e. Disomic for mouse chromosome 11 maternally inherited.
f. Disomic for mouse chromosome 11 paternally inherited.
12. Paternal inheritance of autosomal dominant Huntington disease tends to result in earlier onset than maternal inheritance. Is it valid to refer to this phenomenon as "imprinting"? Justify your answer. (You may need to go back to the notes for lecture 7 to fully answer this question)
13. What happens to maternal imprinting during spermatogenesis? How can this be demonstrated?
14. What happens to maternal imprinting during oogenesis? How can this be demonstrated.
15. Describe an example of imprinting in humans.
16. Explain how the same deletion can cause Prader-Willi syndroms when inherited from a male and Angelman syndrome when inherited from a female.
17. Interpret the following human karyotypes as completely as you can. including gender and phenotype:
a. 47, XXY
b. 46, XY, 5p-
c. 46, XX, t(14q,21q)
d. 47, XY, +21
e. 45, X0
f. 46, XX, 15(q11-q13)-
18. What is the Philadelphia chromosome and what genetic property does it have that is thought to be responsible for malignancy?
19. What is position effect and what are its genetic consequences?
20. How many chromosomes would you expect a translocation carrier of Down syndrome to have? Explain your answer.
21. Explain how uniparental disomy can arise in humans. What are the consequences of uniparental disomy for human chromosome 15?
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