05b: Chromosomes Flashcards
The short arm of the chromosome is called:
The P arm
The long arm of the chromosome is called:
The q arm
Location of centromere in meta centric chromosome
Middle
Chromosome has nearly equal P and q arms.
Location of centromere in submetacentric chromosome
Closer to one side, so P arms shorter than q arms
Location of centromere in acrocentric chromosome
Very close to one end of chromosome (almost no p arm)
The less condensed the chromosomes are, the (less/more) bands appear.
More
A(n) (X) stain is used to image chromosomal banding patterns.
X = giemsa
Dark chromosomal bands are gene (rich/poor) and has which type of chromatin?
Poor; heterochromatin
Light chromosomal bands are gene (rich/poor) and has which type of chromatin?
Rich (50+ genes per band); euchromatin
(Heterochromatin/euchromatin) is lightly packed and actively transcribed.
Euchromatin
Chromosomes can be profiled based on:
- Size
- Centromere position
- Banding pattern
What are the tissue sources used to profile chromosomes?
- Blood (somatic cells)
- Cheek swab (somatic cells)
- Amniocentesis/CVS (prenatal screen)
A normal male karyotype would have what nomenclature?
46, XY
Multiple fertilization could result in (X)ploidy. Give potential nomenclature for this individual.
X = tetra- (4n)
96, XXXX
Presence of an abnormal number of chromosomes, but does not include a difference of one or more complete sets of chromosomes (just certain genes).
Aneuploidy
Nondisjunction usually associated with (sperm/oocytes/both equally).
Oocytes
At what maternal age does incidence of trisomy start to skyrocket?
34-35
Why would mitotic post-zygotic nondisjunction be (more/less/equally) severe as meiotic nondisjunction?
Less severe! Cell with just one chromosome usually won’t contribute
A male with trisomy 18 would have what nomenclature?
47, XY, +18
In DNA microarray, what’s being compared/assessed?
Compare quantity of DNA between normal control sample and fetal sample
What do the colors in DNA microarray indicate?
Yellow: equal amount DNA
Red: extra amount DNA
Green: missing amount DNA
In DNA microarray, is the sample or probe or neither fixed?
Probes fixed, wash sample over them
Nuclear genome accounts for over (X)% of human genome.
X = 99
Mitochondrial genome allows the organelle to synthesize its own (X), that function in:
X = proteins
Cell respiration (ETC)
Why are (nuclear/mitochondrial) genes especially susceptible to mutation?
Mitochondrial;
Respiration and oxidative phosphorylation produce substantial amounts of reactive oxygen species (ROS), which damage DNA
What’s mitonuclear match?
Nuclear genes match rates of mutation/evolution of mitochondrial genes in order for the proteins to co-evolve and keep machinery in sync
Define heteroplasmy.
Tissues, within same individual, vary with the amount of mutant mitochondria since the segregation isn’t regulates
Why are mitochondria inherited through (paternal/maternal) descent only?
Maternal;
Inherited with the cytoplasm (eggs contain 100,000 and sperm only 100)
T/F: a cell with a few mutant mitochondria may have normal phenotype.
True - must pass threshold for phenotypic expression
Analysis that detects small deletions and duplications (less than 0.5 million bp).
Chromosomal microarray
Analysis that detects deletions and duplications greater than 7-10 million bp.
Karyotype
Which analysis can detect both copy number variation and positioning?
Karyotype (NOT microarray)
Edwards syndrom, aka (X), has which key symptoms?
X = trisomy 18
Clenched fist (2nd finger overlaps 3rd), low-set ears, mental retardation, cardiac malformations
Trisomy 13 is also called:
Patau syndrome
Trisomy 21 is also called (X). A male patient would have the nomenclature:
X = Down syndrome
47, XY, +21
What’s a chromosomal translocation?
Chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes
Example of female with Robertsonian translocation nomenclature:
46, XX, t(14; 21), +21
An individual with chromosomal translocation (i.e. Robertsonian) has how many chromosomes?
46
T/F: You can be an asymptomatic carrier of Robertsonian translocation.
True
T/F: Aneuploidy is only really found in autosomal chromosomes.
False - in sex chromosomes also
How do mammals carry out dosage compensation for sex chromosomes?
X-inactivation
Genes subject to escaping X-inactivation are found on (p/q/both) arm(s).
Primarily on P-arm
T/F: Genes that escape X-inactivation are expressed in two copies for males as well as females.
False - only in females
The only viable monosomy, (X), has the nomenclature:
X = Turner syndrome
45, XO
OR… 46, XX, i(Xq)
Give example of a syndrome that results, despite X-inactivation.
Klinefelter’s syndrome
List the two types of chromosomal inversions.
- Paracentric (not involving centromere)
2. Pericentric (involving centromere)
Consequence of paracentric inversion in offspring.
Unbalanced offspring AND genomic instability (one chromosome has no centromere, the other has two)
Consequence of pericentric inversion in offspring.
Unbalanced offspring
What’s one assay that’s especially useful to look for translocations?
Spectral Karyotyping (SKY) with 24 different color labels for each chromosome
A Philadelphia chromosome is the result of (balanced/unbalanced) (X). What disease associated?
Balanced;
X = reciprocal translocation
Chronic myelogenous leukemia
What defines a balanced translocation?
Cells still diploid (no extra/missing chromosomal material)
(X) fusion protein, a result of a (Y) translocation, is problematic in that it:
X = bcr-abl Y = reciprocal
Acts as kinase in wrong time/place
T/F: Vast majority of reciprocal translocations create Philadelphia chromosome.
False
Principles of X-inactivation:
- Random choice of Xi
2. If one X is defective, choice no longer random
If an X chromosome is defective, how is priority set for the Xi chosen?
- Preserve activity of one entire X chromosome equivalent
2. Preserve autosomal sequences, if possible
What defines an isochromosome?
Structural abnormality in which the chromosome are mirror images of each other
5p15 chromosomal deletion:
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