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37 Cards in this Set

  • Front
  • Back
Differentiate between constitutional and acquired chromosome abnormalities.
constitutional: arise before, at, or very shortly after conception

acquired: in somatic cells, some time after conception, in child or adult)
Define aneuploidy.
added or missing chromosomes
Define metacentric, submetacentric, and acrocentric.
metacentric- if two arms of chromatids are of relatively equal length

submetacentric- if one arm is distinctly shorter than the other

acrocentric- very short p arms which contain specialized structures, called STALKS
What is unique to acrocentric chromosomes and which chromosomes are they?
contain stalks, tandem repeats of ribosomal DNA sequences.

13, 14, 15, 21, 22
Define nucleolar organizing regions (NOR).
also known the stalk regions, because they interact to form the nucleolus
What are satellites?
They are distal to the stalk and contain highly repetitive DNA (with no known coding sequences).
List several sample types that one can obtain for clinical cytogenetics.
bone marrow, peripheral blood, fibroblast, amniotic fluid, chorionic villus (extraembryonic tissue)
What are the two requirements of a cell type for their chromosomes to be studied?
1. a nucleus is present
2. the cells are actively dividing
Name the various banding methods. Which banding method is the most commonly used for cytogenetics?
Q-banding, G-banding, C-banding.

G-banding most commonly used.
What is Q-banding, include the name of the dye.
Quinacrine, a dye, is used to produce a banding pattern of chromosomes--requires fluorescence microscopy with UV light. A-T rich sequences stain brightly.
What is G-banding and what is used in this staining?
trypsin used to give staining pattern for each chromosome. Giemsa produces pattern of alternating light and dark bands
What is C-banding mainly used for and how does it stain?
used mainly for staining centromeres of chromosomes; heterochromatin (highly repetitive DNA with no coding sequences) stained dark and euchromatin (regions of coding sequences) stained light.
What is fluoresence in situ hybridization (FISH) and what is it the method of choice for?
DNA probe labelled with biotin or digoxigenin to identify chromosomes or to identify deletions for a particular syndrome.

Method of choice for diagnosis of microdeletion and microduplication syndromes.
Name the different types of probes used and briefly describe them.
SINGLE COPY/LOCUS SPECIFIC PROBES- used for specific questions regarding number, presence, integrity, absence or location of a unique DNA sequence

SUB-TELOMERE-SPECIFIC PROBE- LOOKS FOR TELOMERES?

ALPHOID/CENTROMERIC REPEAT PROBE- help identify specific chromosomes with a satellite DNA (

WHOLE CHROMOSOME PROBES- used to "paint" a whole chromosome or whole chr. arm
New molecular cytogenics allows for what? What is it useful for?
simultaneous "painting" of all chromosomes, each with a distinct color--- allows inspection of the entire genome and useful for the study of complex chromosomal rearrangements in cancer patients.
What is comparative genome microarray analysis?
targets the detection of chromosomal abnormalities by performing hundreds of DNA hybridizations at once to detect small chromosome imbalances in one experiment
Name the different types of numerical chromosome abnormalities.
trisomies (47 chr.), monosomies (45 chr.), triploidy (69 chr.), tetraploidy (92 chr.)
What is the most common trisomy at conception?
trisomy 16
What is the most common monosomy? What is this syndrome called?
45, X (Turner Syndrome)
Define the concept of mosaicism. Often seen in numerical chromosome abnormalities or structural chromosome abnormalities?
When two or more cell lines in an individual get mixed together, as a result of mitotic nondisjunction. Somatic mosaicism leads to an abnormal phenotype.

Often seen on numerical chr. abn.
Most cancers are initiated by which type of chromosome abnormality? (constitutional or acquired)
acquired
Define terminal deletion.
one break in one chromosome arm.
What is the most common and first described terminal deletion in humans?
5p-syndrome (Cri-du-chat syndrome)
Define interstitial deletions. Name some common microdeletion syndromes.
two breaks in one chromosome arm. then the two sticky ends rejoin.

common syndromes: Prader-Willi syndrome, DiGeorge syndrome, Williams syndrome, Smith-Magenis syndrome
Define reciprocal translocations
if two breaks occur in two different chromosomes at same time-- broken ends exchange and rejoin
Does a balanced rearrangement (alternate segregation) have phenotypic consequences?
no, but these individuals are at risk for producing abnormal gametes through segregation errors in meiosis
What is malsegregation?
adjacent segregation where adjacent centromeres of chromosomes that have undergone reciprocal translocations travel together (adjacent-1 or adjacent-2). These typically have more severe consequences.
What is a Robertsonian translocation?
special class of translocations that form between two acrocentric chromosomes (13, 14, 15, 21, 22).
What is the genetic defect in Down's Syndrome?
Trisomy 21
What is an inversion?
two breaks in one chromosome. The piece between the breaks inverts and rejoins.
In an inversion, what is the clinical outcome?
since it is balanced rearrangement and no chromosomal material is gained/lost, this produces no abnormal phenotype.
What is the major factor contributing to numerical abnormalities? What syndrome is the one exception?
Advanced maternal age

exception: Turner syndrome (chromosome being lost most likely from father)
Define non-disjunction
aberrant segregation of homologous chromosomes into the same daughter cell (ie. at meiosis I or II)
Dispermy is the most common cause of triploidy. What is dispermy?
when an ovum is fertilized by TWO SPERM to yield a triploid zygote
In terms of inversions, what is pericentric and paracentric?
pericentric- 2 breaks on either side of the centromere; involves centromere

paracentric- does not involve centromere bc two breaks on same arm of chromosome
What are the results of recombination in pericentric vs. paracentric inversions? Talk about viability of products.
pericentric- duplication deficiency chromosomes; LARGER THE INVERSION, THE MORE VIABLE IT IS

paracentric- acentric (no centromeres) and dicentric (two centromeres) chromosomes; PRODUCTS NOT VIABLE (MISCARRIAGE)
Define cryptic chromosome abnormalities
telomeric rearrangements that lead to mental retardation