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Molecules and Cells II > Cytogenetics and Testing > Flashcards

Cytogenetics and Testing Flashcards

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1
Q

Test that focuses on the centromere of the chromosome

A

C- banding

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2
Q

What is mosaicism?

A

Two or mor chromosome complements in the same person (i.e both a normal chromosome count and an abnormal chromosome count)

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3
Q

Patient presents with short stature, edema at birth,broad chest, webbed neck, increased weight and obesity. What is the most likely diagnosis? What is karyotype? What is the likelihood of survival? What is the cause? What other symptoms may be present?

A

Turner syndrome- 45, X

1% chance of survival.

Usually due to paternal non-disjunction

Additional symptoms: Low hariline, low-set ears, gonadal dysgenesis, small fingernails, deficiency in spatial perception, widely spaced nipples

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4
Q

P arm is basically non existence

A

Acrocentric

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5
Q

Test used to identify Dark regions vs. Lighter regions? What region do the darker regions represents? The lighter regions?

A

G- Banding Giemsa, Q-banding

Darker- heterochromatin (AT rich)

Lighter- Euchromatin (CG RICH)

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6
Q

Variation in # of chromosome sets.

What are the different types?

A

Polyploidy

Triploid- 3 x the haploid # (69)

Tetraploid- 4 x the haploid # (92)

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7
Q

Will efforts that are in place to reduce the birth of children with Tay Sachs disease affect the carrier frequency as well??

A

No. Carrier frequency will still be the same but if those carriers don’t mate then the affected frequency will decrease.

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8
Q

Patient presents with cleft lip/ palate, flexed fingers with polydactyly, bulbous nose, low-set malformed ears, holoprosencephaly. What is the most likely diagnosis? What is karyotype? What is the likelihood of survival? What other symptoms may be present?

A

Patau Syndrome- 47, XY, +13

Lethal in the 1st year of life

Additional symptoms: Hypoplastic ribs, scalp defects, visceral and genital anamolies, cerebral malformation, small abnoraml skull, ocular hypotelorism

*Patau Syndrome has 13 letters!

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9
Q

Which groups are acrocentric? All other groups are___________.

A

D and G

Metacentric

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10
Q

Which type of triploidy aborts earlier?

A

Digyny

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11
Q

How are chromosomes arranged? How are they grouped?

A

Largest to smallest

According to the position of the centromere

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12
Q

Should screening be done based on ethnicity?

A

No! Because there’s a lot of admixture and genes don’t know color

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13
Q

Foresight is what type of screening technique?

A

Expanded carrier screening

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14
Q

What event leads to production of a patiral hydatidiform mole?

A

Fertilization of an ovum by two sperm leading to an abnormal placenta

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15
Q

What is the cause of edema seen in Turner’s syndrome?

A

A blockage in the lymphatic system

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16
Q

A mutation in MSH16 is associated with what type of cancer?

A

Colon cancer

*Can also be associated with breast cancer

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17
Q

Causes of a complete mole

A

› More commonly due to doubling of haploid sperm at fertilization of anucleate egg

› Complete paternal UPD

› Rarely, two haploid sperm fertilizing an anucleate ovum

› Enlargement of the trophoblast ( forms the placenta)

› Overgrown placenta with little to no non-placental elements

› If recurring, may be due to lack of maternal imprinting of otherwise normal conceptus – autosomal recessive trait

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18
Q

__________% of babies with down syndrome are born to mothers under 35.

A

80

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19
Q

What event leads to a tetraplod cell?

A

Occurs when you have a diploid egg and two sperm fertilize it

VERY RARE

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20
Q

Patient presents with failure to thrive at birth, hypotonia, develop veracious appetite in early childhood, and obesity. What is the most likely diagnosis? What is karyotype? What is the cause? Additional symptoms?

A

Prader-Willi syndrome- 46, XY, del (15) (q11-q13)

Paternal deletion of long arm of 15th chromosome

Small hands and feet, hpogonadism, mental disability

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21
Q

Vertical patter on inheritance

Number of males= number of females

Male to male transmission

Every affected child has an affected parent

A

Autosomal dominant

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22
Q

Burkitt Lymphoma

A

B- cell tumor of the jaw

Due to translocation of chromosomes 8 and 14 at q24 and q32

Results in increased unregulated expression of MYC

* Note: the immunoglobulin heavy-chain is located on 14q32, so you can imagine that there will be problems with B cells

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23
Q

Role of Ideograms

A

mapping system that allows them to refer to specific portions of particular chromosomes with extreme accuracy

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24
Q

Patient presents with g, cat like crying, low birth weight, microencephaly, hypertelorism, epicanthal folds, and micrognathia. What is the most likely diagnosis? What is karyotype? What is the cause? What are additional symptoms?

A

Cri du chat syndrome- 46, XY, del(5)(p14.2)

Cause: Delection of short arm of chromosome 5

Additional symptoms: low set ears

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25
Q

What is the concept of rescuing during UPD?

A

Cell realizes that it has too many chromosomes and tries to “kick one out”. The cell has to be sure to kick out the right chromosome though, to insure that there is one maternal chromosome and one paternal chromosome.

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26
Q

What are the causes and characteristics of deletion or duplication?

A

Deletions or duplications may be terminal or intersitial.

Causes:

  • Breakage and loss of centromere segment
  • Unequal crossing over between misaligned homologous chromatids
  • Abnormal segregation of translocation
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27
Q

Vertical pattern

Number of males= number of females

All affected females’ children are affected (none of affected males’ children are affected

A

Mitochondrial

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28
Q

What test are used for prenatal diagnosis?

A

Amniocentesis- the sampling of amniotic fluid using a hollow needle inserted into the uterus, to screen for developmental abnormalities in a fetus.

Chrorionic villus sampling- another way to test the placenta

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29
Q

Horizontal pattern of inheritance

Number of males= number of females

Consanguinity increases risk

A

Autosomal recessive

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30
Q

Patient presents with partial hydatidoform mole. What is the most likely disorder? What is the most likely cause of the disorder? What are the visible attributes of the partial hydatidorm mole?

A

Diandry (69, XXX or 69, XXY or 69, XYY)

1 egg is fertilized by two sperm possibly due to genterically determined weakness of the zona pellucida that allows to sperm to fertilize.

Partial hydatidiform mole presents with a large placenta with degenerate chorionic villi that form fluid-filled sacs

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31
Q

Nondisjunction at which stage of meiosis is worse? Why?

A

Meiosis I. If nondisjunction occurs at Meiosis I, you will produce cells that are only trisomy or monosomy because it prevents separation of homologous chromosomes. Nondisjunction at Meiosis II will produce two diploid cells, 1 monosomy, and 1 trisomy. Fetus has a greater chance of being normal

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32
Q

Vertical pattern

All daughters of affected males are affected, but none of the sons

Number of females> number of males

No male to male transmision

Often fatal in males

A

X- linked dominant

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33
Q

Patient presents with hypotonia, flat face, slanted palpebral fissures, epicanthic folds. What is the most likely diagnosis? What is karyotype? What is the likelihood of survival? What is the cause? What other symptoms may be present?

A

Down syndrome- 47,XX, +21

Nondisjunction during Meiosis I

1/600 births

Additional symptoms:

  • Pelvic dysplasia, cardiac malformations
  • Short, broad hands, transverse crease, hypoplasia

of 5th finger, intestinal atresia, high arched/cleft palate

*Legal age to Drink is 21!

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34
Q

Different triploidy karyotypes. Which is most common?

A

69,XXX

69, XXY

69, XYY (most common)

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35
Q

In what disorder is the carrier frequency for AA males 1/10?

A

G6PD

36
Q

A ring chromosome can be a cause of what syndrome? What is the cause of ring chromosomes

A

Turner syndrome

Defect in telomeres

37
Q

For which population (s) are hemoglbinopathy (SC, SS, beta thalassemia) screened for?

A

African American

West african

Hispanic

Italian

38
Q

Which part of the Barr Body still remains active and still codes for proteins?

A

Pseudoautosomal region (PAR)

39
Q

Only males affected, related though carrier females

No male to male transmission

Lyonization leading to affected females

Apparent male to male transmission

A

X-Linked Recessive

40
Q

In a pedigree, the first affected individual in the family who brought the family to medical attention is the ________.

A

Proband

41
Q

The WAS gene can cause spectrum of hematopoietic disorders like:

A

Wiscott-Aldrich Syndrome

Eczema

Microthrombocytopenia

Severe and recurrent infections

42
Q

P arm slightly shorter than q arm

A

Submetocentric

43
Q

Trisomy X is the result of________. In Trisomy X about ______ of patients have some learning problems.

A

Maternal nondisjunction meiosis I; 70%

44
Q

Importance of XIST gene?

A

Expressed in inactivation X chromosomes.

*lack of this gene can be indicative of Turner’s syndrome

45
Q

Patient presents with head-body dispropotion with head relatively large and small, an abnormal placenta, and syndactyly of third and fourth fingers. What is they likely problem? What are the possible karotypes? What is cause?

A

Digyny- 69, XXX or 69, XXY

Due to nondisjuntion of an entire chromosomes set at meiosis I or Meiosis II that causes a binucleate, diploid oocyte.

46
Q

Which chromosomes are acrocentric?

A

13,14,15, 21, 22

47
Q

You want to detect microscopic deletions and visualize obvious chromosome anomalies. Which test should you use? How does it work? What are the limitiations?

A

Fluorescence in-situ hybridization

Nucleic acid probes are hybridized to unique chromosomal DNA sequences. Probes are labed with fluorescent dye, which is visible under a specific wavelength. Can be used in metaphase and anaphase.

Limitations: Does not provide information on point mutations or other small genetic aberrations

48
Q

What is an example of a gene outside of PAR that does not have a similar copy on the Y chromosome and is therefore expressed in higher levels in females?

A

Steriod sulfatase

*think calice cat*

49
Q

In ideograms, orientation is based on the ________. Where are lower numbers located?

A

Centromere; Proximal to the centromere

50
Q

Primary role of staining chromosomes

A

To study peripheral blood lymphocytes and chromosomes during mitosis

51
Q

What is a Robersionian translocation?

A

Translocation between two acrocentric chromosomes

52
Q

Which usually more harmful deletions or duplications?

A

Deletions

53
Q

You want to be able to detect very small deletions or duplications. Which test should you use? How does it work?

A

Coparative genomic hybridization

Flourophore-tagged DNA from the patient is applied to the microarray.

54
Q

Patient presents with a tall, thin stature, hypogonadism, gynecomastia, infertility due to failed germ cell development. What is the most likely diagnosis? What is karyotype? What is the likelihood of survival? What is the cause? What other symptoms may be present?

A

Klinefelter syndrome- 47, XXY

Chances of survival are very high

Due to in part to paternal meiosis I and also in part to maternal meiosis I

Additional symptoms: Variable learning problems, poor psychosocial development

*48, XXYY; 48, XXXY; 49, XXXXY tend to be more severe

55
Q

Symbolism for Robertsonian Translocation

A

der,t, rob

Derivative translocation of acrocentric chromosomes

56
Q

You want to look at genetic material of the fetus through the maternal serum. You also want to be able to determe which chromosomes those DNA fragments came from. Which test should you use? What are the benefits of this test? How is chromosomal origin identified?

A

Cell free DNA anaylsis

Non-invasive

Detection rates close to 99%

Chromosomal origins are identified through massive parallel shotgun sequencing

57
Q

Which type of aneuploidy abnormality has the highest frenquency of miscarriages? Which has the lowest?

A

45, X

XXX, XXY, XYY (often not discovered until person tries to procreate)

58
Q

Patient presents with attention deficits, hyperactivity, impulsiveness. Patient is tall. What is the most likely diagnosis? What is karyotype? What is the likelihood of survival? What is the cause? What other symptoms may be present?

A

47, XYY

High chance of survival

Due to paternal nondisjunction meiosis II

Additional symptoms: Normal fertility, normal intelligence but speech and other therapies may be needed

59
Q

In which type of inversion is the risk for carrying an abnormal viable offspring higher? Why?

A

Pericentric; If you have a pericentric inversion those chromosomes cannot line up in metaphase becuase the centromere has changed its location and the genes are on opposite side!

Dats Brazy!

60
Q

Histone Octamer components

A

Two copies of H2A, H2B, H3, and H4

61
Q

For which population (s) is Tay-Sachs Disease screened for?

A

Ashkenazi Jewish

French Canadian

62
Q

Phildelphia chromosome

A

Due to translocation of chromosomes 9 and 22 at q34 and q11.

Leads to longer ABL (tyrosine kinase) protein with enchanced activity and actiation of oncogene BCR

63
Q

What is the chance of a healthy sibling of an affected person with an AR condition to be a carrier?

A

2/3

64
Q

What two events can occur to lead to a triploid cell? Which is more common?

A
  1. 1 egg is fertalized by 2 sperm (most common)
  2. A haploid egg is fertilized by one diploid sperm (less common)

*Very selective process so usually diploid sperm aren’t able to fertilize an egg

65
Q

If you want to look at large chromosome delections and duplications and chromosome structure. What test should you use?

A

Karyotype

66
Q

Which information should be collected in the family history for a pedigree?

A

Three generations

Half versus full siblings

Age, birthdate, or year of birth

Relevant health information

Diagnosis, age at diagnosis

Age at death or years of birth/death

Cause of death

Ethnic background for each biological grandparent

67
Q

In pedigree, person seeking genetic services is the _________

A

Consultand

68
Q

Patient presents with low body weight, closed fists, rocker-bottom feet, hypertonia, microcephaly and cardiac and renal malformations. What is the likely diagnosis? What is karyotype? What is the likelihood of survival? What are additional symptoms?

A

Edwards Syndrome- 47, XY, +18

95% of cases are lethal in the 1st yr

Additional symptoms: Narrow hips with limited abduction, short sternum, prominent occiput, micrognathis, fine/ small facial features, mental retardation

*The legal age to Elect someone is 18!

69
Q

Patient presents with short stature, severe mental disability, spascitty, seizures, and uncontrollable laughter. What is the most likely diagnosis? What is karyotype? What is the cause?

A

Angelman Syndrome- 46, XX, del (15)(q11-q13)

Maternal deletion of long arm of 15th chromosome

“maternal imprinting”

70
Q

Example of a disorder that results from isochromosomes.

A

Pallister Killian syndrome- 47, XY,i (12p)

Symptoms: extremely weak muscle tone in infancy and early childhood, intellectual disability, distinctive facial features and sparse hair, areas of unusual skin pigmentation

*You’ve killed a whole arm of genetics.

71
Q

What is the chance of conceiving a child with down syndrome at age 35?

A

1/238

72
Q

What’s the difference between a screening and diagnostic?

A

Screening- Identifies those at risk for a particular outcome

Diagnostics- Provide confirmed result that an individual has a medical condition of interest or genetic anomaly

73
Q

What are the limitations of Whole Genome/ exome sequencing?

A

Insuffiecient capture of some exons

No triplet repeat, large deletions or duplications, translocations, or inversions are detected

74
Q

In the second trimester of pregancy what proteins can be screened for to determine down syndrome of the fetus? What would the tests show for other types of aneuploidy?

A

hCG (high), Unconjugated estriol (low), Inhibin A (high), and dimeric protein A (Low)

Trisomy 18 (Edwards)

hCG (very low), Unconjugated estriol (low), Inhibin A (unchanged), and dimeric protein A (unchanged)

Trisomy 13 (Patau)

hCG (normal), Unconjugated estriol (normal), Inhibin A (normal), and dimeric protein A (increased)

Turner (45X)

hCG (very high), Unconjugated estriol (decreased), Inhibin A (very high), and dimeric protein A (decreased)

75
Q

Importance of telomeres

What happens when they are missing/malfunctioned?

A

Maintain chromosome stability

Keep ends from being degraded by nucleases

When missing, there is a pause in cell cycle to allow error to be corrected or may indicate pathway to apoptosis

76
Q

Types of genetic screenings

A

Carrier screening (commonly used for prenatal or preconception testing)

Prenatal screening (for 1st and 2nd trimester screening, sequential screening, and cell free DNA screening)

Screening to determine complex disease risk (for multifactorial conditions)

77
Q

Patient presents with progressive neurological disorder, loss of sensation and wasting of muscles in the feet, legs, and hands, due to damaged peripheral nerves. What is the most likely diagnosis? What is karyotype? What is the cause?

A

Charcot- Marie-Tooth- 46, XY, dup(17)(p12)

Duplication of chromosome 17

* Think we have 29 teeth, 17 at the top and 12 at the bottom

78
Q

What is UPD? Why is this a problem?

A

Cell has either chromosomes that are both from the mother or both from the father. Mother and father both pass on important genes, some genes are only expressed on paternal chromosome and some genes are only expressed on maternal chromosome (imprinting).

79
Q

You are not concerned with the entire chromosome but you want to study single, specific gene. What test should you use? What diseases can detected for which this test? What are the limitations?

A

Single gene/ specific mutation testing

Can detect for CF, SCD, and DMD

Limitations: You may test the wrong gene based off of certain symptoms, which could allow for a misdiagnosis.

80
Q

When are prenatal testing procedures used?

A

For the couple who is a 1 in 4 or higher risk

81
Q

Type of inversion that includes centromere

A

Pericentric

82
Q

Patient presents with congenital heart disease, characteristic facial features, learning difficulties, and immune deficiency. What is the most likely diagnosis? What is karyotype? What is the cause?

A

Velocardiofacial syndrome/ DiGeorge Syndrome

Karyotype: 46, XX, del(22)(q11.21-q11.23)

Due to deletion of 22q11

83
Q

You want test a phenotype associated with multiple genes at the same time. What test should you use? What diseases can be tested using this test?

A

Multi-gene panel testing

Deafness, mental disability, seizures, ataxia, and autism

84
Q

For which population (s) is Maple Syrup Urine Disease screened for?

A

Mennonite/ Amish

85
Q

P and q arms roughly the same size

A

Metocentric

86
Q

For which population (s) is cystic fibrosis screened for?

A

Caucasian

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