Chapter Fourteen: Chromosomal Rearrangements Flashcards
two events that reshape genomes
- rearrangements
- changes in chromosome number
DNA sequences are reorganized within one or more chromosome
chromosomal rearrangement
loss or gain of entire chromosomes or sets of chromosomes
changes in chromosome number
karyotypes usually remain ___ within a species
constant
most genetic imbalances result in a ___
selective disadvantage
related species usually have ___ karyotypes
different
closely-related species differ by ___
a few rearrangements
distantly-related species differ by ___
many rearrangements
there is a correlation between karyotypic rearrangements and ___
speciation
four types of chromosomal rearrangements
- deletion
- duplication
- inversion
- reciprocal translocation
rearrangements that add or remove base pairs
deletion and duplication
rearrangements that relocate chromosomal regions without changing the number of base pairs
inversion and reciprocal translocation
___ and ___ can cause all four types of rearrangement
DNA breakage and aberrant crossing over
mistakes in rearranging antibody genes can lead to ___
cancer
___ can detect large chromosomal rearrangements
fluorescent in situ hybridization (FISH)
___ has probes specific for two different chromosomes to show chromosomal translocation
spectral karyotyping (SKY)
___ is produced by using FISH probes for particular regions of chromosomes
multicolor banding
what is the ultimate way to determine if any chromosomal rearrangements are present
sequencing
in an organism with a deletion, ___ reads would be detected in that section; in an organism with a duplication, ___ reads would be detected in that section
fewer
more
whole genome sequencing can detect all rearrangements because ___
it will point out sequences that are not normally next to each other
the precise base pairs at which rearranged chromosome segments begin and end
rearrangement breakpoints
rearrangement breakpoints can be identified by ___
PCR and sequencing
PCR analysis for rearrangement breakpoints is ___ and ___
inexpensive and sensitive
deletion on both chromosomes
deletion homozygosity
homozygosity for deletions is often ___ or ___
lethal or harmful
the effect of a homozygous deletion depends on ___ and ___
size of deletion and affected genes
deletion on one chromosome
deletion heterozygosity
deletion heterozygotes can have a mutant phenotype due to ___
gene dosage effects (haploinsufficiency)
what is haploinsufficiency
only one functional gene does not produce enough protein for the normal phenotype
in deletion heterozygotes cells become vulnerable to ___ that will impact the ___
mutations
remaining normal chromosome
if a deletion heterozygote carries a recessive allele on the normal chromosome, the organism will display the ___ phenotype
recessive mutant
deletions can be used to locate ___
genes
examining the phenotype of a deletion heterozygote can tell you ___
where a specific gene is
if the phenotype of the gene is mutant, you know the gene must lie ___ the deleted region; if the phenotype is wild-type, you know the gene must lie ___ the deleted region
inside
outside
edits genes by precisely cutting DNA and then letting natural DNA repair take over
CRISPR
___ form in the chromosomes of deletion heterozygotes
deletion loops
recombination between homologs can occur only at regions of ___
similarity
no ___ can occur within a deletion loop
recombination
because of deletion loops, ___ will not be accurate
genetic map distances
why do deletion loops form in deletion heterozygotes
genes on the normal homolog don’t have a sequence to match up with on the chromosome with the deletion
most duplications have ___ phenotypic consequences
no
why do most duplications produce normal phenotypes
increased gene copy number or altered expression in new chromosomal environment
homozygosity or heterozygosity for a duplication can be ___ or ___ depending on ___ and ___
lethal or harmful
size of duplication and affected genes
unequal crossing over between duplicated regions on homologous chromosomes can result in ___ and ___ copy number
increased and decreased
repeats of a chromosomal region that lie next to each other, either in the same order or reverse order
tandem duplications
repeats of a chromosomal region that are not next to each other
nonrandom duplications
nonrandom duplications can be on the ___ or ___ from the original copy
same chromosome or a different chromosome
with some genes, an abnormal phenotype can be caused by an imbalance in ___
gene dosage
the ___ gene in drosophila is extremely dosage sensitive
notch+
haploinsufficient and duplication heterozygotes for the notch+ gene have a ___
mutant phenotype
in unequal crossing over, one chromosome ends up with a ___ and the other ends up with a ___
duplication
deletion
most inversions result in ___
normal phenotype
two reasons inversions can result in an abnormal phenotype
- inversion disrupts a gene
- inversion takes place near regulatory sequences for other genes or near heterochromatin
inversions can act as crossover ___
suppressors
in inversion heterozygotes, no viable offspring are produced that carry chromosomes resulting from ___
recombination int he inverted region
___ can produce inversions
chromosome breakage
inversion in which the centromere is within the inverted segment
pericentric inversion
inversion in which the centromere is not within the inverted segment
paracentric inversion
___ form in inversion heterozygotes
inversion loops
in an inversion loop, one chromosomal region rotates to conform to the ___
sequence of its homolog
formation of inversion loops in meiosis allows the ___ of homologous regions
tightest possible alignment
crossing over within the inversion loop produces ___
aberrant recombination chromatids
paracentric and pericentric inversion heterozygotes both result in ___
reduced fertility
in pericentric inversion heterozygotes, each recombinant chromatid ___, but each will be ___
has a centromere
genetically imbalanced
zygotes formed from normal chromosomes with chromosomes with these recombinant chromatids will be ___
nonviable
in paracentric inversion hetrozygotes, one chromosome ___ and the other ___
lacks a centromere
has two centromeres
zygotes formed from normal chromosomes with chromosomes with these dicentric recombinant chromatids will be ___
nonviable
which is worse: pericentric or paracentric inversion
paracentric
inversions act as crossover ___
suppressors
only gametes that did not recombine with inversion loop are ___
viable
crossover suppression is used to make ___
balancer chromosomes
balancer chromosomes are used for ___
genetic analysis
balancer chromosomes have ___, ___ inversions
multiple, overlapping
in balancer heterozygotes, no viable recombinant progeny will be produced because of ___
crossover suppression
attach part of one chromosome to a non homologous chromosome
translocation
parts of two nonhomologous chromosomes switch places
reciprocal translocation
reciprocal translocations result in ___ of genetic material
no loss
reciprocal translocations usually result in ___ phenotype
normal
reciprocal translocations may result in mutant phenotype if breakpoint is ___
within or near a gene
reciprocal translocations may result in decreased ___
fertility
a reciprocal translocation is the genetic basis for chronic ___
myelogenous leukemia
leukemia patients have too many ___
white blood cells
in a translocation homozygote, chromosomes segregate ___ during meiosis I
normally
is the breakpoints of a reciprocal translocation do not affect gene function, there are no ___ in homozygotes
genetic consequences
in a translocation heterozygote, the two haploid sets of chromosomes carry ___ arrangements of DNA
different
chromosome pairing during prophase I of meiosis is maximized by formation of a ___
cruciform structure
three chromosome segregation patterns are possible for translocation heterozygotes
- alternate
- adjacent-1
- adjacent-2
balanced gametes are produced only by ___ segregation
alternate
in reciprocal translocation heterozygote, only the ___ segregation pattern results in viable progeny
alternate
___ is observed in heterozygotes with reciprocal translocation
pseudolinkage
translocation arising from breaks at or near the centromeres of two acrocentric chromosomes
robertsonian translocation
in robertsonian translocations, the small chromosome may be ___
lost from the organism
___ can arise from a robertsonian translocation between chromosomes 21 and 14
down syndrome
any segment of DNA that evolves the ability to move from place to place within a genome
transposable elements (TE)
Marcus Rhoades and Barbara McClintock inferred existence of TEs from genetic studies of ___
corn
TEs have been found in ___
all organisms
TEs were previously considered to be selfish DNA because they ___
carried no genetic information useful to the host
it is now know that some TEs have evolved ___
functions beneficial to the host
TE length ranges from ___ to ___
50bp to 10kb
TEs can be present in ___copies per genome
hundreds of thousands
discoverer of TEs
Barbara McClintock
molting of corn kernels is caused by ___
movements of a TE into and out of pigment gene
two types of TEs
- retrotransposons
- DNA transposons
three types of retrotransposons
- long interspersed elements (LINEs)
- short interspersed elements (SINEs)
- human endogenous retroviruses (HERVs)
LINEs and SINEs have ___
poly-A tails
HERVs have ___
long terminal repeats
HERVs are similar in structure to ___
retroviruses
retrotransposons move via ___
RNA intermediates
LINEs and HERVs have a gene encoding ___
reverse transcriptase
the reverse transcriptase gene is a clue that LINEs and HERVs ___
move via an RNA intermediate
retrotransposons move via ___
RNA intermediates
experiment done with ___ proved that retrotransposons move via RNA intermediates
Ty1 retrotransposon of yeast
Ty1 with an intron was cloned into a ___
plasmid
all new insertions of the Ty1 into the genome ___
lacked the intron
the intron must have been removed by ___
splicing from an RNA
five steps of how an LTR retrotransposon moves
- transcription of retrotransposons
- synthesis of cDNA by reverse transcriptase
- staggered cut made in genomic target site
- retrotransposon cDNA inserts into target site
- original copy remains while new copy inserts into another genomic location
TEs whose movement does not rely on an RNA intermediate
transposon
most DNA transposons contain ___ and ___
inverted repeats of 10-200bp long at each end and a gene encoding transposase
recognizes inverted repeats (IRs) and cuts at the border between the IR and genomic DNA
transposase
transposase catalyzes the movement of ___
DNA transposons
genes often contain ___ copies of TEs
defective
many TEs sustain ___ during the process of transpositions or after transposition
deletions
if a deletion removes the promoter for retrotransposon transcription, ___
it cannot generate the RNA intermediate for future movements
if the deletion removes one of the inverted repeats at the end of a transposon, ___
transposase will be unable to catalyze transcription
deletions can create ___ TEs that cannot ___
defective
transpose again
non-deleted TEs that can transpose on their own
autonomous TEs
defective TEs that require the activity of non-deleted copies for the TE for movement
nonautonomous TEs
TEs can disrupt ___ and alter ___
genes
genomes
TE insertion can result in an altered phenotype if ___ or ___
it is inserted within the coding region of a gene or if is inserted near a gene
TE associated alleles can be ___
unstable
TEs can trigger spontaneous ___
chromosomal rearrangements
there can be ___ between two copies of the same TE pair
unequal crossing over
transposition can cause gene ___
relocation
mutations in eye color of drosophila because of TE insertions depend on ___ and ___
which TE is inserted and where it is inserted
gene relocation due to transposition can occur when two copies of a TE integrate in ___
nearby locations on the same chromosome
alternative splicing of transposase gene limits ___
TE movement
one splice produces ___, another splice produces ___; these two compete to ___
transposase
repressor of transposition
bind to the inverted repeats
chromosome rearrangements are sources of ___
variation
genes at or near rearrangement breakpoints may have new ___ or be ___
patterns of expression
fused with another gene
transposable elements can alter ___ or ___
patterns of expression or inactivate a gene
sets of related genes with slightly different functions
gene families
gene families most likely arose from ___
gene duplications
