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MHG - Exam 2 > Lecture 22-Cytogenetics 1 > Flashcards

Lecture 22-Cytogenetics 1 Flashcards

1
Q

Euchromatin is largely composed of ______ sequences vs. heterochromatin which is largely composed of _______ sequences.

A
  • coding

- non-coding

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2
Q

Heterochromatin is largely found where?

A
  • centromeres

- distal end of Y

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3
Q

Each centromere has how many bps?

A

171

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4
Q

Are all centromeres the same?

A

no, they can differ from chromosome to chromosome

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5
Q

Chromosomes 13, 14, 15, 21, 22 all have what structure?

A

acrocentric

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6
Q

Describe an acrocentric chromosome.

A
  • no euchromatin on P arm
  • has many repeats of rRNA genes so it can be very large or non-existant
  • these genes are redundant among acrocentric chromosomes
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7
Q

If someone has trisomy they have ____ chromosomes.

A

47

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8
Q

If someone has monosomy they have ____ chromosomes.

A

45

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9
Q

What are 3 ways to get cells from a fetus in order of lowest to highest rate of miscarriage?

A
  • amniocentesis
  • CVS
  • PUBS (percutaneous umbilical blood sample)
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10
Q

When is peripheral blood not used for diagnosis of congenital abnormalities?

A
  • PUBS

- Acquired abnormalities like leukemia

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11
Q

Phytohemagglutinin (PHA)

A

mitogen to stimulate WBCs in peripheral blood to divide so they can get to metaphase for analysis

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12
Q

What is bone marrow tissue used for with respect to diagnostic testing?

A

leukemia

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13
Q

When is a skin biopsy usually used? What is it’s caveat?

A
  • to compare karyotypes between skin and blood

- takes a long time to growth them in culture and therefore before preparation can be done

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14
Q

If you draw someones blood you could expect their WBCs to be in what phase?

A
  • G0
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15
Q

What are the chromatid counts (per chromosome) at the end of each phase of the cell cycle?

A
  • G1: 1
  • S: 2
  • G2: 2
  • M: 1
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16
Q

What happens during prometahpase?

A

nuclear envelope disappears

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17
Q

What is the difference between the nuclear spindle attachments between prophase and prophase I?

A
  • prophase: one chromosome/spindle

- prophase I: homologous chromosomes/spindle

18
Q

colcemid

A

spindle fiber poison that freezes cells in metaphase

19
Q

What do you need to do with cell samples prior to Giemsa staining?

A
  • trypsin digest of some chromosomal proteins
20
Q

When does independent assortment take place?

A
  • meiosis 1
21
Q

reduction division

A
  • occurs during meiosis 1

- is the halving of chromosomes from 46–>23

22
Q

What is the law of independent assortment?

A

largely maternal chromosomes and largely paternal chromosomes can be grouped together in the same gamete

23
Q

At least 1 _____ is required for regular orientation of the chromosomes on the spindle during meiosis I.

A

chiasma

24
Q

Other than mixing of genes, chiasmata do what?

A
  • stabilize chromosomes on the spindles and decrease the risk of nondisjunction
25
Q

Where are chiasmata not seen?

A

on acrocentric chromosomes

26
Q

How do the number of meiotic divisions differ between males and females?

A

men have more divisions that are subdivisions of prophase 1. This is where crossing over occurs

27
Q

Female gamete synthesis stops where first? When does it resume?

A
  • prophase 1, resumes in the 1st half of the menstrual cycle

- meiosis completes at fertilization

28
Q

What is the difference in outcomes of meiosis in females vs. males?

A
  • females have 1 gamete made/meiosis

- males make 4/meiosis

29
Q

Constitutional abnormalities (cytogenic abnormalities present at CONCEPTION) are associated with ____ (2)

A
  • birth defects

- miscarriages

30
Q

What is the most common and clinically significant type of chromosome disorder? What is it’s frequency?

A
  • aneuploidy

- 3-4%

31
Q

How does aneuploidy arise?

A
  • nondisjunction
32
Q

How can you tell which parent gave the aneuploidy in trisomies?

A
  • you can’t tell
33
Q

Majority of aneuploidies are from _____, when?

A

the mom during meiosis 1, nondisjunction is more common in females

34
Q

Downs syndrome accounts for what percent of chromosomal abnormalities at birth?

A

50%

35
Q

Kids with downs are at increased risks for what 2 things?

A
  • leukemias

- congenital heart defects

36
Q

Do you need 47 chromosomes to have a trisomy 21?

A

no, you can have a translocation so the third copy of 21 is attached to another chromosome

37
Q

Describe the viability of Trisomy 18 and 13.

A
  • 5% live to 1 year old
38
Q

Which trisomy is associated with midline defects?

A
  • Trisomy 13
39
Q

What are the phenotypes associated with autosomal abnormalities? (4)

A
  • developmental delay/MR
  • facial features more characteristic fo the syndrom than of family members
  • growth delay
  • congenital malformations
40
Q

Why do the phenotypes associated with sex chromosome abnormalities tend to be milder than autosomal abnormalities?

A
  • fewer genes on sex chromosomes and most have to do sex development
41
Q

Which sex chromosome abnormalities do not result in infertility? Are they pretty harmful to those affected?

A
  • XXX, XYY

- fairly benign: just the typical abnormal heigh, lower IQ

42
Q

What can aberrant crossover between sex chromosomes cause? How?

A
  • sex reversal: if the SRY gene gets translocated it results in sex reversal

MHG - Exam 2 (11 decks)

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