Flashcards in Cytogenetics Deck (31):
What letters represent the short and long arms of a chromosome?
Short arm: p, Long arm: q
What is a metacentric chromosome?
The short and long arm are equal in size
What is a sub-metacentric chromosome?
The short and long arm are unequal in size.
What is an acrocentric chromosome?
The short arm is very small and close to the centromere.
What is the most common technique that is used for blood karyotyping? Describe the process.
G-bandin - Lymphocytes (T-cells) from peripheral blood are stimulated with phyohemaglutinin (PHA) and cultured for 72 hours before being placed in a hypotonic solution (KCl) to arrest division. Cells are then fixed on slides with methanol/acetic acid. Banding is achieved by trypsin treatment for G-bands and staining with Giemsa. Results in GC rich light bands and AT rich dark bands
What do del, dup, mar, stand for?
Deletion, duplication, marker
Describe what the karyotype 46,XY,del(5)(p15.2) indicates.
Male with normal number of chromosomes who has a deletion of part of the short arm of one of his chromosome #5s.
What karyotype does a Turner syndrome patient have?
45,X (females) - this is a monosomy X
What karyotype does a Klinefelter syndrome patient have?
47, XXY (males)
What karyotype does a female with trisomy 21 (Down syndrome) have?
What is euploidy?
Normal, balanced set of chromosomes
What is diploidy?
Normal number of chromosomes in a somatic cell (2n)
What is haploid?
Chromosome number of gametes in mature egg or sperm (1n so it can be 23,X or 23, Y in humans)
What is aneuploidy?
Unbalanced number of chromosomes, where either one is missing or you have an additional chromosome (2n-1 or 2n+1) Ex: trisomy 21
What is triploidy? What are the three ways it can occur?
3 haploid sets (3n)
1) Dispermy - ovum is fertilized by two sperm to yield a triploid zygote (most common cause)
2) Fertilization by diploid sperm
3) Non-disjunction in the egg
What is polyploidy?
Having extra sets of chromosomes
Ex: triploidy: 68,XXX or 69,XXY
What are the two potential consequences of triploidy?
1) 2 maternal + 1 paternal = normal fetal development, small placenta
2) 2 paternal + 1 maternal = abnormal fetal growth, increased placental development
What is nondisjunction?
The aberrant segregation of homologous chromosomes into the same daughter cell - occurs most often in Meiosis I of oogenesis and is associated w/ advanced maternal age
What is mosaicism? What are the two different types?
Mixture of two or more cell lines in an individual (Ex: 45,X/46,XX) May result from error in disjoining of chromatids in mitosis
Constitutional mosaicism - numerical chromosome abnormalities
Gonadal mosaicism - involves testes and ovaries
Describe what yellow, red, and green mean in a Comparative Genomic Hybridization Array (aCGH)/chromosome microarray.
Red - patient has less DNA than the control (deletion)
Green - patient has more DNA than the control (duplication)
Yellow - DNA is equal in patient and control
Describe what the 0 line is in the Array profile and what marks in the negative and positive direction indicate.
0 line = normal
Left of 0 line/negative = deletions
Right of 0 line/positive = duplication
What are some of the limits of microarray methodology?
Cannot detect balanced rearrangements, does not provide information regarding location of additional copy, copy number variations may or may not be pathogenic
What is fluorescence in situ hybridization (FISH)?
Complementary stretch of DNA (probe) is labeled and hybridized onto a cell. FISH can then identify specific chromosomal regions that have been deleted or duplicated - location specific. It is used clinically as a confirmation for diagnoses from microarray studies.
What are the two types of chromosomal deletions? And given an example of each.
Terminal - at ends of chromosomes (Wolf-Hirschorn Syndrome, deletion on chromosome 4)
Interstitial - in middle of chromosomes (Smith-Magenis syndrome, deletion on chromosome 17)
What is a chromosomal duplication and what are the two different types?
Duplication is when a visible chromosomal segment is present twice on the same chromosome.
What is Williams Beuren Syndrome? What happens when a duplication occurs in this same chromosomal region?
Interstitial microdeletion of chromosome 7 - CV disease, distinctive face, overfriendliness, ADD
If duplication occurs in same chromosomal region, result is autism
What are the two types of inversion duplication?
Pericentric - 2 breaks on either side of centromere - results in duplication deficiency chromosomes
Paracentric - 2 breaks on same chromosome arm, not involving centrome - results in acentric and dicentric chromosomes
What are ring chromosomes?
Deletion of terminal short arm and terminal long arm results in the unstable ends rejoining
What is a translocation?
Exchange or transfer of chromosomal segments between two ore more chromosomes.
What is a Robertsonian translocation?
Originates through joining of long arms of acrocentric (centromere is at end of chromosome instead of the middle) chromosomes 13,14,15,21, and 22