Chromosome Structure Flashcards
What is a chromosome composed of?
one very long, double-stranded DNA molecule.
What is a metacentric chromosome?
centromere is close to the middle of DNA molecule
What are the acrocentric chromosomes in humans?
13,14,15,21,22
p arm has a special structure that contains all the ribosomal RNA genes. It is ok to be missing one or more acrocentric short arms and still be perfectly normal.
What is a submetacentric chromosome?
centrosome is off-center.
What is the p-arm? q-arm?
p-arm is the shorter arm of a submetacentric chromosome. Q-arm is the longer one.
During what phase of mitosis are chromosomes analyzed under a microscope?
metaphase. They become more condensed as it continues.
What are balanced abnormalities?
novel rearrangement containing the net normal amount of genetic material. Normal phenotype, but reproductive risk
What is an unbalanced abnormality?
arrangement associated with extra or missing genetic material. High likelihood of phenotypic abnormality.
What is partial trisomy?
a structural abnormality that results in 3 copies of a particular chromosome segment.
What is partial monosomy?
only one copy of a chromosome segment
What does de novo mean?
new. (not from the parent)
What does familial mean?
structural abnormalities that segregate through a pedigree in a balanced form, occasionally creating unbalanced offspring
What does constitutional mean?
present in all cells of the body
What does acquired mean?
arises in somatic cell of single tissue typically applied to cancer lineages
What are Robertsonian translocations?
central fusions of the long arms of acrocentric chromosomes
What are reciprocal translocations?
chromosomes swap pieces. Two breaks, reciprocal exchange of segments between two nonhomologous chromosomes. sometimes results in stable division if each piece ends up with a centromere and telomeric ends.
What would be the chromosome number for a patient with a balanced robertsonian translocation?
45, because two chromosomes that used to be separate are now fused
What is a pericentric inversion?
2 breaks in different arms of a chromosome. Inversion piece includes centromere
What is a paracentric inversion?
2 breaks in same arm and a piece flips and reattaches upside down
What is a n interstitial deletion?
two breaks in the same arm and piece is lost from chromosome
Are deletions balanced or unbalanced changes?
unbalanced.
What is a terminal deletion?
single break and loss of broken terminal segment. Telomeres heal and regenerate
What are isochromosomes?
unbalanced abnormality that is the result of misdivision at the centromere during metaphase/anaphase. Division occurs transversely instead of longitudinally. You get two copies of the p arm in one chromosome and one with 2 q arms.
Causes a partial trisomy and a partial monosomy
What is an important clinical example of isochromosomes?
Turner syndrome 46,X,i(Xq)
Down syndrome 46,,XY,i(21q)
What is duplication?
small segment of chromosome is duplicated in one chromosome, resulting in partial trisomy.
Is duplication a balanced change?
no
Would you expect a phenotype abnormality in a person with a pericentric inversion?
no, inversions do not alter phenotype, but present a reproductive risk
What would a t(9;22) cause?
translocation between 9 and 22 causes CML (chronic myelogenous leukemia)
Which sex has a higher risk of nondisjunction?
female. usually nondisjunction errors are received from the mother
Which trisomies are most likely to produce a live infant with an unbalanced karyotype?
21 most likely.
13 is possible, but very very low risk because pregnancies fail.
Which trisomies are most likely to produce a live infant with an unbalanced karyotype?
21 most likely. 13 also, but results in much more pre-birth deaths
