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Biochemistry Exam #4 > Clinical Cytogenetics > Flashcards

Clinical Cytogenetics Flashcards

1
Q

What is cytogenetics the study of?

A

Chromosomes and chromosomal abnormalities

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2
Q

What two issues are chromosomal abnormalities the leading cause of?

A
  • Intellectual disability syndromes

- Pregnancy loss

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3
Q

What is another name for the small arm and long arm of a chromosome?

A
  • Small arm: p

- Long arm: q

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4
Q

What is polyploidy? What is triploidy?

A

Polyploidy: gain of one or more entire chromosome sets

- Triploidy: cells with 3 copies of each chromosome (3N for 69 chromosomes total)

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5
Q

What is aneuploidy? What is the primary cause of aneuploidy?

A

Aneuploidy: loss or gain of a single chromosome
- Cause: nondisjunction (failure to separate) during either meiosis I or meiosis II resulting in gametes with 1 extra or 1 less chromosome than normal

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6
Q

Define monosomy. What are the outcomes of monosomies in autosomal and sex chromosomes?

A

Monosomy: only one copy of a specific chromosome (1 is lost)

  • Autosomeal monosomies are ALWAYS lethal
  • Only X chromosome monosomy is survivable
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7
Q

Define trisomy. What three trisomies are compatible with survival, and why? What is the most common of these three?

A

Trisomy: three copies of a specific chromosome (1 is gained)

  • 13, 18 and 21 are the only survivable trisomies because these three chromosomes have the fewest genes (so while there are more genes than usual, it is not too much for the body to handle)
  • Trisomy 21 is the most common
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8
Q

What are two alternative names for Trisomy 21?

A

Trisomy 21 = Down Syndrome = 47, XY + 21 or 47, XX + 21

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9
Q

What are the 12 characteristics of Down Syndrome?

A
  • Intellectual disability
  • Almond-shaped eyes
  • Eye abnormalities
  • Flat nasal bridge
  • Hearing loss
  • Protruding tongue
  • GI tract obstruction
  • Congenital heart defect
  • Increased risk for respiratory infection
  • Increased risk for leukemia
  • Alzheimer’s-like symptoms late in life
  • Male sterility
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10
Q

What are the two causes of Down Syndrome, and what is the percentage caused by each?

A
  • Nondisjunction causes 95% of cases

- Robertsonian translocation causes the other 5% of cases

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11
Q

What are two alternative names for Trisomy 18?

A

Trisomy 18 = Edward Syndrome = 47, XY + 18 or 47, XX + 18

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12
Q

What are the 11 characteristics of Edward Syndrome?

A
  • Small eyes/mouth
  • Receding jaw
  • Low-set ears
  • Intellectual/developmental disability
  • Clenched fists/overlapping fingers
  • Rocker-bottom feet
  • Flexed big toe
  • Low weight for gestational age
  • Diaphragmatic hernia
  • Congenital heart defects
  • Kidney defects
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13
Q

What is the cause of Edward Syndrome?

A

ONLY nondisjunction

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14
Q

What are two alternative names for Trisomy 13?

A

Trisomy 13 = Patau Syndrome = 47, XY + 13 or 47, XX + 13

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15
Q

What are the 7 characteristics of Patau Syndrome?

A
  • Cleft lip/palate
  • Small abnormal eyes
  • Large triangular nose
  • Extra fingers/toes
  • Deafness
  • Microcephaly
  • Intellectual/developmental disability
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16
Q

What are the two causes of Down Syndrome, and what is the percentage caused by each?

A
  • Nondisjunction causes 95% of cases

- Robertsonian translocation causes the other 5% of cases

17
Q

Are autosomal chromosome abnormalities or sex chromosome abnormalities tolerated better?

A

Sex chromosome abnormalities are better tolerated

18
Q

What does gene expression look like in a normal females versus a female with sex chromosome abnormalities?

A

Normal females have one copy of most genes of the X chromosome are expressed and two copies of the genes in PARs are expressed
- In a female with sex chromosome abnormalities, there is either increased or decreased gene dosage or PARs

19
Q

What are two examples of sex chromosome abnormality disorders? Provide an alternative name for each

A
  • Turner Syndrome = 45, X

- Klinefelter Syndrome = 45, XXY

20
Q

Describe what is happening in terms of gene expression and gene dosage in Turner Syndrome

A

With Turner Syndrome, only one X chromosome is present so only one copy of PAR genes is expressed
- Decreased gene dosage because only 50% of PAR gene products are available

21
Q

What are the 10 characteristics of Turner Syndrome?

A
  • Short stature
  • Small lower jaw
  • Broad/webbed neck
  • Low hairline at back of neck
  • Visual impairments
  • Ear infection/hearing loss
  • Learning disabilities (no intellectual disabilities)
  • Hypothyroidism
  • Congenital heart defects
  • Ovarian insufficiency
22
Q

What are the two treatments for Turner Syndrome? Explain why each is recommended

A
  • Growth hormone: bone growth genes are found on PAR regions, which are lacking
  • Estrogen replacement: ovarian insufficiency leads to a lack of sex hormones
23
Q

Describe what is happening in terms of gene expression and gene dosage in Klinefelter Syndrome

A

With Klinefelter Syndrome, there is an extra copy of all PAR genes gained on the X chromosome
- Increased gene dosage due to an extra X chromosome

24
Q

What are the 8 characteristics of Klinefelter Syndrome?

A
  • Tall stature with long arms/legs
  • Weaker muscles
  • Poor coordination
  • Gynecomastia
  • Learning disabilities
  • Speech/language problems
  • Infertility
  • Hypogonadism/Androgen deficiency
25
Q

Because characteristics of Klinefelter Syndrome are often subtle, what is the most common (and often only) symptom?

A

Infertility

26
Q

What are the three treatments for Klinefelter Syndrome? Explain why each is recommended

A
  • Testosterone therapy: for hypogonadism and Androgen deficiency
  • Speech therapy: speech and language problems
  • Physical therapy: weaker muscles and poor coordination
27
Q

What normally happens with male chromosomes during recombination? What is the issue with recombination involving XX male and XY females?

A

In males, X and Y chromosomes pair and undergo recombination using the PAR regions - just proximal to the PAR region on Y chromosomes is the SRY gene
- Errors can occur during recombination causing crossover to occur below the SRY gene (transferred to X)

28
Q

Describe what is happening with the SRY gene in XX male and XY females

A
  • In XX males, the SRY gene is present on one of the X chromosomes so there is male development but the SRY gene causes issues on other genes of that X chromosome
  • In XY females, the SRY gene is not present so there is female development
29
Q

What is translocation? What are the two types?

A

Translocation: loss or duplication of PARTS of a chromosome

  • Reciprocal translocations
  • Robertsonian translocations
30
Q

What is a reciprocal translocation, and what does it result in (hint: 2 step process)?

A

Reciprocal translocation: first, there are chromosomal breaks on two different chromosomes, then the broken chromosomes exchange the material that was broken off, resulting in derivative chromosomes

31
Q

What are the two types of reciprocal translocation? How does each present phenotypically?

A
  • Alternate segregation: two normal or two abnormal chromosomes in the gamete (usually no phenotype because all genetic information is present equally)
  • Adjacent segregation: one normal and one abnormal chromosome in the gamete (abnormal phenotype)
32
Q

What is a Robertsonian translocation? What type of chromosomes are involved and what five numbers?

A

Robertsonian translocation: loss of short arms of two acrocentric chromosomes and the fusion of the long arms at the centromere
- Acrocentric chromosomes: 13, 14, 15, 21, 22

33
Q

What is the typical phenotype for Robertsonian translocation? Why is this?

A

Typically, normal phenotype because the short arms contain redundant genetic material

34
Q

What is the typical chromosome count seen with Robertsonian translocation?

A

One fewer chromosome in total (loss of 2 normal chromosomes and gain of 1 Robertsonian chromosome)

35
Q

With translocation, how does the patient with the abnormality typically present phenotypically? What about that patient’s offspring?

A

Often with reciprocal translocation and Robertsonian translocation, the person affected typically does not exhibit a phenotype BUT THEIR OFFSPRING WILL

Biochemistry Exam #4 (10 decks)

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