Final Exam Flashcards
(41 cards)
What percentage of DS is due to trisomy 21 like in karyotype?
95% of cases involve trisomy 21.
90% involve maternal meiosis, MI
10% involve paternal meiosis, MII
A woman is a carrier of a balanced Robertsonian translocation between chromosomes 14 and 21. On average, how many of her gametes will be viable?
50%
A woman and her brother are carriers of a balanced Robertsoniantranslocation
between chromosomes 14 and 21. Who has the highest risk to have a child
with Down syndrome?
Risk is always higher to a female.
The woman with the translocation has a baby with Down
Syndrome. How many chromosomes does this baby have? How many
copies of chromosome 21?
The baby has 46, with 3 copies of chromosome 21 (third 21 has 14 stuck to it, there is only one 14 by itself - so three 21 and only one 14 in the end still 46 chromosomes)
A man has a child with Prader-Willi syndrome. His sister has a child with Angelman syndrome. How do you explain this?
They are each carriers of a balanced translocation involving chromosome 15. PWS is paternal chromosome 15 70% of the time. AS is maternal chromosome 15 70% of the time
Thinking about Turner syndrome:
- What would the karyotype show?
- How many are spontantously aborted?
1.
45, X
2.
99%
What is unique about Turner syndrome?
How many Barr bodies would you see?
Only viable monosomy in humans.
0 (zero) Barr bodies (b/c only one X chromosome even exists)
Who is phenotypically normal?
- 45, X
- 45, XX, t(14;21)
- 46, XX
- 46, XY
- 46, XX, t(14;21), +21
- 47, XXY
Normal:
- 45, XX, t(14;21)
- 46, XX
- 46, XY
Abnormal:
- 45, X - Turner’s Syndrome
- 46, XX, t(14;21), +21 - Robertsonian Down syndrome
- 47, XXY - Kleinfelter
What is the worst Robertsonian translocation you can imagine? Why?
(21;21)
Fetus will almost always have Down syndrome
unless there is also nondisjunction by other parent
In what disorder does nondisjunction always occur in male meiosis II?
47, XYY (XYY Male)
Why would someone have a karyotype?
Problems of early growth and development (ambiguous genitalia)
Dysmorphic features (something different about how they look)
Stillbirth and neonatal death
Fertility problems, both male and female
Family history of chromosome abnormalities
Neoplasia
Pregnancy in woman of advanced maternal age
When is genetic testing of minors usually ok?
For conditions that can manifest before age 18
It has been reported that type I osteogenesis imperfecta (OI) patients with dentinogenesis imperfecta (DI) are more likely to have fractures at birth than those without DI. What is the underlying molecular mechanism for type I OI with DI? A.Gain of function. B.Haploinsufficiency C.Loss of function D.Dominant negative
D. Dominant negative
You need to figure out where to send a patient sample for genetic testing.
What resource can you use to find an appropriate lab?
Genetic Testing Registry
A couple present for genetic counseling after the birth of their son who has a multifactorial trait for which females are more commonly affected. Regarding recurrence risks, what do you tell them?
a. Their recurrence risk is higher than if a daughter had been affected, and the subsequent risk is higher for a daughter than a son.
b. Their recurrence risk is higher than if a daughter had been affected, and the subsequent risk is higher for a son than a daughter.
c. Their recurrence risk is lower than if a daughter had been affected, and the subsequent risk is higher for a daughter than a son.
d. Their recurrence risk is lower than if a daughter had been affected, and the subsequent risk is higher for a son than a daughter.
e. The recurrence risk is 50%
a.Their recurrence risk is higher than if a daughter had been affected, and the subsequent risk is higher for a daughter than a son.
What is triploidy?
69 chromosomes.
Most common mechanism is fertilization of ovum by 2 sperm.
Babies can be born but don’t live long
What is tetraploidy?
92 chromosomes. Karyotype is 92, XXXX or 92, XXYY (failure of completion of early cleavage division of the zygote). Embryos, no babies. 3x less common than triploidy.
Phenocopy?
Phenotype produced by exposure to environmental agent that
looks like genetic disorder
Polygenic?
Multiple genes contribute to phenotype, usually each with a
small contribution; important in complex traits like diabetes
Multifactorial?
Genes and environment contribute to phenotype
Genes and environment contribute to phenotype
- Number of affected individuals: more = higher risk.
- severity: more severe = higher risk.
- If individual is of sex least affected, recurrent risk is higher.
How is genetic testing different from other types of medical tests?
It has implications for other family members.
What does whole exome sequencing primarily focus on?
Coding regions (exons) of known genes - about 2% of the genome
What bill was passed to try and prevent genetic discrimination in
obtaining a job and health insurance?
Genetic Information Nondiscrimination Act (GINA)