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Genetics > Review 3 > Flashcards

Review 3 Flashcards

1
Q

If we did a karyotype on a Down Syndrome patient, what would we most likely find?

A
  • An EXTRA copy of chromosome 21 that would lead to a developmental disorder.
    “Trisomy 21”

-3 copies of each of its genes instead of 2.

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2
Q

What percentage of DS is due to trisomy 21 like in karyotype?

A
  • 95% have 47 chromosomes involve trisomy 21
  • 90% involve maternal meiosis, MI (Maternal non-junction)

-10% involve paternal meiosis, MII
(Paternal)

5% Robertsonian translocation

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3
Q

A woman is a carrier of a balanced Robertsonian translocation between chromosomes 14 and 21. How many chromosomes does
she have?

A

45
-Two are joined together
in order not to have phenotypical consequences

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4
Q

A woman is a carrier of a balanced Robertsonian translocation between chromosomes 14 & 21. On average, how many of her
gametes will be viable?

A

50%

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5
Q

A woman and her brother are carriers of a balanced Robertsonian translocation
between chromosomes 14 & 21.

Who has the highest risk to have a child w/ Down syndrome?

A

Risk is always HIGHER to a FEMALE because one ovum per tons of sperm

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6
Q

The woman with the baby with the translocation has a baby with DownSyndrome.

-How many chromosomes does this baby have?
-How many
copies of chromosome 21?

A

The baby has 46, with 3 copies of chromosome 21.

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7
Q

A man has a child with Prader-Willi syndrome. His sister has a child w/ Angelman syndrome. How do you explain this?

A

They are each carriers of a balanced translocation involving chromosome 15

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8
Q

Thinking about Turner syndrome:

What would the karyotype show?
How many are spontaneously aborted?

What is unique about Turner syndrome?

How many Barr bodies would you see in individual with Turners?

A
  • 45, X Sex Chromosome Aneuploidy
  • 99% aborted; Occurs in 1/4000 females;
  • Only viable monosomy in humans
  • 0 inactivated x chromosomes
  • S/S: webbed neck, short stature, broad chest w/ widely spaced nipples
  • Can be seen in X-linked recessive disorders and affected females
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9
Q

Who is phenotypically normal?
(If not normal, what is the disorder?)

45, X
45, XX, t(14;21)
46, XX
46, XY
46, XX, t(14;21), +21
47, XXY
A

No; 45, X (Turner’s Syndrome)

Yes; 45, XX, t(14;21) (Robertsonian translocation)

Yes; 46, XX

Yes; 46, XY

No; 46, XX, t(14;21), +21 (Down’s)

No; 47, XXY (Klinefelter’s)
-(One barr body)

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10
Q

What is a Robertsonian translocation?

A
  • Unusual chromosome rearrangement caused by 2 particular chromosomes joining together.
  • 2 of 5 afrocentric chromosomes have broken at the beginning of the short arm near the point where it meets long arm. (Chromosomes: 13, 14, 15, 21, 22)
  • The long arms fused together. Chromosome then consists of 2 long arms but no short arms.
  • Need 45 chromosomes to be viable

–Will have 50% chance of passing on to children

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11
Q

What are the genetic changes related to Klinefelter’s syndrome?

A

Klinefelter syndrome results from the presence of 1 EXTRA copy of the X chromosome in each cell (47,XXY).

  • Occurs in 1/1000 male births
  • 50% from paternal errors (M1)
  • 50% maternal errors (M1 or M2)
  • Usually infertile
  • One of X chromosomes is inactivated (Barr body)
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12
Q

In what disorder does nondisjunction always occur in male meiosis II?

A

47, XYY

  • Occurs in 1/1000 live male births
  • Always occurs in Paternal nondisjunction at MII
  • Tall, normal IQ, normal fertility
  • Clinical phenotype is normal
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13
Q

Why would someone have a karyotype done?

A

1) Problems of early growth & development (ambiguous genitalia)
2) Dysmorphic features (something different about how they look)
3) Stillbirth & neonatal death
4) Fertility problems, both male & female

5) Family history of chromosome abnormalities (Ex: PW syndrome)
Except NOT for CF or Single Gene Disorders

6) Neoplasia
7) Pregnancy in woman of advanced maternal age

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14
Q

When is genetic testing of minors usually ok

A

-For conditions that can manifest before age 18 (Not including breast cancer)

Ex: (Colon cancer)

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15
Q

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

A

D. Dominant negative

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16
Q

You need to figure out where to send a patient sample for genetic testing.

-What resource can you use to find an appropriate lab?

A

Genetic Testing Registry

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17
Q

A couple present for genetic counseling after 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, & the subsequent risk is higher for a daughter than a son.
b) Their recurrence risk is higher than if a daughter had been affected, & the subsequent risk is higher for a son than a daughter.
c) Their recurrence risk is lower than if a daughter had been affected, & the subsequent risk is higher for a daughter than a son.
d) Their recurrence risk is lower than if a daughter had been affected, & the subsequent risk is higher for a son than a daughter.
e) The recurrence risk is 50%

A

a. Their recurrence risk is HIGHER than if a daughter had been affected, & the subsequent risk is HIGHER for a DAUGHTER than a son.
- Pushes you higher on the liability threshold, because least affected sex is affected, but daughter is still more commonly affected.

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18
Q

Tell me about triploidy

A
  • 69 chromosomes (23x3)
  • Most common mechanism is fertilization of ovum by 2 sperm
  • Babies can be born but don’t live long
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19
Q

Tell me about tetraploidy

A

-92 chromosomes (23x4)

-Karyotype is 92, XXXX or 92, XXYY (FAILURE of completion of early cleavage
division of zygote)

  • Embryos, no babies
  • 3x less common than triploidy
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20
Q

What is Phenocopy?

A

-Produced by exposure to ENVIRONMENTAL agent that looks like genetic disorder

Ex: (Gingival fibromatosis (HGF) vs. drug induced gingival overgrowth via cyclosporine, calcium channel blockers, & phenoytoin)

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21
Q

What is Polygenic?

A

MULTIPLE genes contribute to phenotype, usually each w/ a

small contribution; important in complex traits like diabetes

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22
Q

What is Multifactorial?

A

Combination of Multifactorial Genes & environment contribute to phenotype

Ex. Different genes found on chromosomes that influence Breast Cancer or Diabetes.

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23
Q

What factors increase recurrence risk for multifactorial trait, like clefting?

A

1) Number of affected individuals: more = higher risk
2) Severity: more severe = higher risk
3) If individual is of sex least affected, recurrent risk is higher

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24
Q

How is genetic testing different from other types of medical tests?

A

It has implications for other family members

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25
Q

What bill was passed to try and prevent genetic discrimination in
obtaining a job and health insurance

A

Genetic Information Nondiscrimination Act (GINA)

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26
Q

What does whole exome sequencing primarily focus on?

A
  • The coding region (exons)

* 1 - 2 % of the genome

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27
Q

What test would you have done for PW?

A
  • Karyotype

- A “FISH” test (fluorescent in-situ hybridization) to detect a deletion

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28
Q

It has been reported that type I osteogenesis imperfecta (OI) patients w/ 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 “WITHOUT” DI?

A. Gain of function.
B. Haploinsufficiency
C. Loss of function
D. Dominant negative

A

B. Haploinsufficiency

29
Q
  1. Answer the following questions regarding translocations as True or False:

a. Robertsonian translocations are translocations between two metacentric chromosomes.
b. Balanced translocation carriers are not at risk to have unbalanced offspring.
c. Of the gametes that a carrier of a (14;21) Robertsonian translocation can make, ½ are not viable.
d. In a female with a translocation between an autosome and the X chromosome, the normal X will be preferentially inactivated.

A
  1. a. False

b. False (infertility problems are often how translocation carriers are ascertained)
c. True
d. True

30
Q
  1. All of the following mechanisms are explanations for why a female may be affected with an X-linked recessive disorder (like hemophilia or Duchenne muscular dystrophy) EXCEPT

a. Skewed X inactivation
b. Uniparental disomy from either an affected father or carrier mother
c. Turner syndrome
d. Consanguinity
e. Mutation in the pseudoautosomal region of the Y chromosome
f. Balanced translocation between an autosome and the X chromosome

A

e; Mutation in the pseudoautosomal region of the Y chromosome
(Skewed X-inactivation most likely)

31
Q
  1. For Prader-Willi syndrome (PWS) and Angelman syndromes (AS)…
    1) Most common mechanism in both disorders _________
A

c. Deletion

32
Q
  1. For Prader-Willi syndrome (PWS) and Angelman syndromes (AS)..
    2) Recurrence risk (RR) if UPD is underlying mechanism _______
A

h. <1/1000

33
Q
  1. For Prader-Willi syndrome (PWS) and Angelman syndromes (AS)..
    3) RR if inherited methylation defect is mechanism_____
A

a. 50%

34
Q
  1. For Prader-Willi syndrome (PWS) and Angelman syndromes (AS)..
    4) Contiguous gene syndrome___________
A

d. PWS

35
Q
  1. For Prader-Willi syndrome (PWS) and Angelman syndromes (AS)..
    5) PWS results from absence of _____ contribution
A

f. Paternal

36
Q
  1. For Prader-Willi syndrome (PWS) and Angelman syndromes (AS)..
    6) AS results from absence of _____ contribution
A

e. Maternal

37
Q
  1. For Prader-Willi syndrome (PWS) and Angelman syndromes (AS)..
    7) Can result from mutation in single gene
A

b. AS

38
Q
  1. For Prader-Willi syndrome (PWS) and Angelman syndromes (AS)..
    8) Test that provides highest detection rate
A

j. Methylation

39
Q
  1. For Prader-Willi syndrome (PWS) and Angelman syndromes (AS)..
    9) RR if deletion is mechanism
A

h. <1/1000

40
Q
  1. For Prader-Willi syndrome (PWS) and Angelman syndromes (AS)..
    10) Technique to detect deletions
A

g. FISH

41
Q
  1. For Prader-Willi syndrome (PWS) and Angelman syndromes (AS)..
    11) Compulsive eating, developmental delay
A

d. PWS

42
Q
  1. For Prader-Willi syndrome (PWS) and Angelman syndromes (AS)..
    12) Seizures, ataxia, inability to talk
A

b. AS

43
Q
  1. For Prader-Willi syndrome (PWS) and Angelman syndromes (AS)..
    13) Mechanism where PWS and AS occur in single family
A

i. Translocation

44
Q
  1. PWS and AS are the best examples in humans of __________?
A

imprinting

45
Q
  1. Triploid fetuses have ______ chromosomes? (Are there any liveborns? Mechanism?)
A

69; live births occur but babies die shortly thereafter; fertilization by two sperm most common

46
Q
  1. Tetraploid fetuses have ______ chromosomes? (Are there any liveborns? Mechanism?)
A

92; No live births; failure of completion of cleavage in early embryo

47
Q

Test your knowledge:

Which one of the seven dwarves had AS?

A
  • Dopey ! :)
  • “He’s silly but sane, with a seizure disorder”

-His understanding of speech is rather good, & manages to express himself by efficient mimic & gesture. “happy puppet”

**So important to determine underlying molecular defect so appropriate recurrence risks can be counseled.

48
Q

What kind of mutations is p.Gly180Arg?

A

missense

49
Q

What kind of mutations is p.Gly180*?

A

nonsense

50
Q

What kind of mutations is p.Gly180Gly?

A

silent

51
Q

p.Gly180Serfs*4

A

frameshift

52
Q

Whole exome sequencing can identify mutations in

a. Promoters
b. Exons
c. Introns
d. Mitochondrial DNA
e. A, b and c

A

Whole exome sequencing mainly detects mutations in coding exons.

53
Q

A male calico cat is the equivalent of what human disorder?

a. Turner syndrome
b. Klinefelter syndrome
c. 47,XYY
d. 47,XXX
e. Down syndrome

A

Klinefelter syndrome

54
Q

Different clinical phenotypes caused by mutations in the same gene is

a. Allelic heterogeneity
b. Clinical heterogeneity
c. Locus heterogeneity
d. Variable expressivity
e. None of the above

A

b. Clinical heterogeneity

Ex: HGF & Noonan Syndrome (which does not present w/ gingival overgrowth b/c of the mutation in SOS1)

55
Q

Mitochondrial DNA can be used to link

a. A woman and all of her children and all of her children’s descendents
b. A woman and all of her children and all of her daughter’s descendents
c. A man and all of his children and all of his children’s descendents
d. A man and all of his children and all of his son’s descendents

A

A woman and all of her children and all of her daughter’s descendants

(Remember only passed on by mother. You can use Y chromosome polymorphisms to trace males. That was what was used to try and determine whether or not Thomas Jefferson fathered a child by his slave.)

56
Q

Which disorder matches with this trinucleotide repeat location:
3’ UTR?

A

-Myotonic

57
Q

Which disorder matches with this trinucleotide repeat location: 5’ UTR

A

-Fragile X

58
Q

Which disorder matches with this trinucleotide repeat location: Intron

A
  • Freidreich ataxia
  • Freidreich ataxia is the only autosomal recessive disorder due to a trinucleotide repeat expansion.

(Remember if a disorder is associated w/ thousands of repeats, it does not occur in the coding region. Also if you have hundreds or thousands of repeats, you need to use Southern blot to determine the # of repeats)

59
Q

Which disorder matches with this trinucleotide repeat location: Coding region (exon)

A

-HD

60
Q

Which statement regarding performing genetic testing on minors is correct?

a. No guidelines exist for performing genetic testing on minors.
b. It is appropriate to test minors for whatever tests the parents request.
c. It is appropriate to test minors for adult onset disorders.
d. It is appropriate to test minors for conditions with onset of symptoms before age 18.

A
  1. d

Remember that minors are only tested for disorders that manifest in childhood

61
Q

Mr. and Mrs. Jones, who are first cousins, have a son w/ cystic fibrosis. They are anxious to learn if their current pregnancy will be affected. Although testing is performed using standard mutation panel, no mutation is found in their son. They opt to have linkage performed (Results show single band(affected male) @ the bottom of gel & top and bottom bands for the rest 3; see Q-14 on review).
You conclude the current pregnancy is

a. Affected (aa)
b. A carrier (Aa)
c. Wildtype (AA)
d. At 50% risk to be affected

A

b; A carrier (Aa)

(The lower band is associated with a. The pregnancy looks just like the parental genotypes and so is a carrier).

62
Q

Couple present for prenatal diagnosis for achondroplasia. Both are heterozygous carriers of the 1138G→A transition, which creates a new restriction site.
-The results show restriction enzyme analysis on the 164 bp PCR product. You conclude:

(PCR results: Mother- 3 bands, Fetus- bottom 2 bands, Father- 3 bands, Uneffected- top band)

a. The fetus has heterozygous achondroplasia.
b. The fetus has lethal achondroplasia
c. The fetus does not have achondroplasia.
d. The fetus is at 50% risk to have achondroplasia.
e. The fetus is at 50% risk to have a lethal form of achondroplasia.

A

b; The fetus has LETHAL achondroplasia

(The fetus only has the two lower bands, representing the cleavage products of the 164 bp PCR product. If the fetus was heterozygous, the wildtype allele should have remained uncut)

63
Q

Which of the following is NOT an indication for chromosome analysis?

a. Baby with ambiguous genitalia
b. Couple who have had 3 or more miscarriages
c. Child with sickle cell anemia
d. Newborn with a heart defect who has features that suggest trisomy 18
e. A woman whose sister is a balanced translocation carrier

A

c; Sickle cell anemia is due to a missense mutation

substitution of one amino acid for another

64
Q

What are the acrocentric chromosomes?

A

13, 14, 15, 21, 22

65
Q

Tell me about euploidy

A
  • Definition: extra copies of all chromosomes; not compatible with long term survival
  • Exact multiple of haploid chromosome number
  • Types:
  • Triploid (3n;69): children do not survive long, results from fertilization by 2 sperm
  • Tetraploid (4n; 92): always 92,XXXX or 92,XXYY suggesting failure of completion of early cleavage division of zygote, cleavage wasn’t complete, babies can’t be born with it
  • Triploidy is 3x more common than tetraploid
66
Q

Tell me about aneuploidy

A
  • Definition: abnormal chromosome number due to an extra or missing chromosome
  • Always associated with clinical phenotype
  • Any other chromosome number that is not an exact multiple of a haploid chromosome
  • Most common and clinically significant type of human chromosome disorder
  • Occurs in 3-4% of all clinically recognized pregnancies and 0.7% of births
  • Most common trisomy in newborns = 21
67
Q

PWS

a. What is the most likely molecular mechanism?
b. She begins taking medicine and starts having regular periods. If she were to get pregnant the risk for her baby to inherit the deleted chromosome is?
c. If she transmits the deleted chromosome to her baby, what will the phenotype be?

A
  • Deletion on paternal 15q11q13 (dad’s chromosome 15)
  • 50%
  • Angelman Syndrome
68
Q

Tell me about multifactorial traits

A
  • Most affected children have unaffected parents
  • Recurrence risk increases with the number of affected children in a family
  • Recurrence risk increases with severity of the defect
  • A more severely affected parent is more likely to produce an affected child
  • Consanguinity slightly increases the risk for an affected child
  • If the two sexes have a different probability of being affected, the least likely sex, if affected is the most likely sex to produce an affected offspring

Genetics (4 decks)

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