Exam 2: Cytogenetic Abnormalities Flashcards
chromosomes are constantly being…
broken and rejoined
sometimes in the wrong way
full breaks of both stands in dsDNA are called
double-strand breaks
the cell has mechanisms for ___ repair
double-strand break
rejoins broken ends
how do chromosome rearrangements arise?
when the wrong ends of broken chromosomes are rejoined
major types of chromosome rearrangement
inversion
translocation
fusion
which rearrangements only happen in G1 when chromosomes consist of only 1 chromatid
inversion
translocation
fusion
breakage
what is an inversion
a piece gets turned around backwards
what is a translocation
two pieces get traded between chromosomes
what is breakage
a piece gets lost (lethal)
what is fusion
two broken chromosomes fuse
what does an inversion result from
two breaks in one chromosome with sequence reversal
what happens if an inversion occurs inside an essential gene?
cell death
do genes function if the DNA they’re located on is in either direction?
yes
when does inversion cause a problem?
during meiosis b/c inversion loops
inversion loop
pairing between inverted and normal segments
permits alignment of all homologous loci
is an inversion loop in a bivalent a problem?
not unless a crossover happens inside the loop
this causes duplications and deletions
if there is a crossover inside the inversion loop, each crossover chromatid will be…
duplicated for everything on one side, outside the loop
and deleted for everything on the other side, outside the loop
everything in the loop will still be present only once
paracentric inversion
centromere outside loop
dicentric and acentric chromosome
pericentric inversion
centromere inside loop
one centromere on each chromosome
how are translocations like inversions
may have no bad effects, if no genes interrupted by breaks
cell could continue to grow and undergo mitosis
meiosis is where problems happen
pairing at meiosis causes a…
pachytene cross
adjacent disjunction types
I: homologous centromeres separate at MI (normal)
II: nonhomologous centromeres separate at MI (abnormal)
adjacent disjunction always gives
1 good and 1 bad chromosome
gametes with duplications and deletions
alternate disjunction
pachytene cross
creates 2 normal gametes and 2 balanced translocation gametes
balanced gametes pass on the…
translocation
offspring are carriers of the translocation
why are they called alternate and adjacent disjunction?
b/c chromosomes involved are either alternate or adjacent to each other in the pachytene cross
when an individual has a balanced translocation he/she will produce
some gametes with duplications/deletions (lethal/highly abnormal)
some completely normal gametes
some gametes with the whole balanced translocation (normal phenotype)
about 7% of families with 2 or more spontaneous abortions have…
a balanced translocation
when a translocation first occurs all the original DNA is…
still there so it’s automatically “balanced”
alternate disjunction can transmit the balanced translocation in normal appearing offspring…
forever
some families pass on balanced translocations for…
generations
ring chromosome
another two-break rearrangement only in G1
both tips broken off and ends are fused (forms a ring)
rare
does a ring chromosome have all the original genes?
yes
can a cell with a ring chromosome be completely normal?
yes, until it divides
what is the problem with ring chromosomes
when sister chromatids exchange in mitosis the ring cannot divide
the centromeres oppose each other causing cell self-destruction
do ring chromosomes retard normal growth?
yes, b/c in cell division the daughters often die
people with ring chromosomes are small
