Topic 7: Chromosome Alterations Flashcards
___________: contain a single chromosome within an arbitrary region that is not bound by any membranes
chromosomal territories
how do we visualize our chromosomes?
with a karyotype! (an individual’s complete set of chromosomes- can now be made into a picture!)
chromosomes 1-22 are ________
autosomes
chromsome 23 is a ___________
sex chromosome (X or Y)
chromosomes are divided at the centromere into _______________
chromosome arms (usually unequal lengths)
short arm = (________)
p arm
long arm = (________)
q arm
_________ chromosomes have a centromere near the middle
metacentric
______ chromosomes have a centromere nearer to one end
submetacentric
_________ chromosomes have centromeres at one end
acrocentric
_________ chromosomes have a terminal centromere
telocentric
________ condensation results in the banding patterns on chromosomes
chromatin
_______: regions of lesser compaction, actively transcribed chromatin
_________: regions of higher compaction, less gene transcription
euchromatin
heterochromatin
_________: when chromosomes and sister chromatids fail to separate properly
nondisjunction
chromosome numbers that are a multiple of the haploid number (2n, 3n, 4n…) are ______
euploid
if we add or remove a chromosome, it alters the euploid number and generates an _______
aneuploid
____________in germ-line cells causes aneuploidy
nondisjunction
nondisjunction in germ-line cells results in the failure of homologous chromosome separation in ________
meiosis I
________ (2n+1): three of one chromosome instead of a homologous pair
trisomy (trisomic)
_______ (2n-1): a single copy of the chromosomes instead of a homologous pair
monosomic
nondisjunction in germ-line cells results in the failure of sister chromatid separation in _______
meiosis II (typically follows after a normal meiosis I)
aneuploidy alters gene dosage, which two men worked on this concept? and with what plant?
Albert Francis Blakeslee and John Belling worked on the Jimson Weed
true/false: aneuploidy changes the gene dosage of ALL the genes on the affected chromosome
true!
in diploid organisms, gene dosage is ____%
monosomic: ______%
trisomic: _________%
100
50
150
true/false: plants aren’t as tolerant to changes in gene dosage compared to animals
false! they are!
where are the three most common chromosomes for trisomy in humans? How many total opportunities for trisomy are there?
trisomy 13, 18, 21
potential for 24 different kinds of trisomy (often see them in sex chromosomes!!)
when does trisomy 21 (Down Syndrome) occur? in what meiotic stage?
what is trisomy 21 linked to?
reaches synapsis in prophase I, then stops (90% of trisomy 21 cases were a result of meiosis I nondisjunction)
linked to the age of the mother
children have two copies of maternal C21, and one copy of paternal C21
what are two examples of gene dosage differences in humans with missing/extra sex chromosomes? (female)
turner syndrome (X0)
triple X syndrome (XXX)
X-inactivation mosaicism occurs from ______ nondisjunction: occurs during embryogenesis early in development
mitotic (example: Turner syndrome)
____________ disomy: both copies of the homologous chromosome pair are derived from the same parent
uniparental (requires nondisjunction of the same chromosome in both the eggs and the sperm!! (super rare!!))
________: the presence of three or more sets of chromosomes
polyploidy (very common in plants!!)
________: have chromosomes derived from a single species
autopolyploids
______: have chromosomes derived from multiple species
allopolyploids
polyploidy results from….
meiotic nondisjunction (2n egg + 1n sperm)
mitotic nondisjunction (doubles chromosome number)
what are the consequences of commercial polyploidy in food?
fruit and flower size increases, reduced fertility (seedless fruits), increase in heterozygotes relative to diploids
development of wheat: the union of diploid genomes of _____ ancestral species
three
true/false: changes to chromosome structure can result in the loss/addition of genes
true! causes gene dosage imbalances, animals are greatly affected by these abnormalities
why are chromosome mutations important?
a common source of genetic variation, a major cause of genetic disorders and conditions, a cause of infertility
what are the main four kinds of mutations?
deletions, duplications, inversions, translocations
what are three things that can lead to chromosome breaks during DNA synthesis/crossing over in meiosis?
external mutagens/chemicals/radiation
transposable bits of DNA (mobile)
recombination errors
true/false: when a break happens, segments of the chromosome can be lost
true
partial chromosome deletion: both strands of DNA are severed at the _____________
chromosome breakpoint (they retain their chromatin structure, can re-adhere to each other)
______ deletion: chromosome end breaks off, containing telomere and additional genetic material
terminal deletion
terminal deletion leaves a chromosome fragment ______
acentric (without a centromere)
cri-du-chat syndrome results in a partial __________
partial deletion heterozygote (one chromosome is wildtype, and the homolog has a terminal deletion)
_____________: The pattern of inheritance in which a single recessive allele is inherited but is still expressed
pseudodominance
________ syndrome displays pseudodominance because the allele on the normal homolog will be phenotypically expressed, instead of the partial deletion
cri-du-chat
_________ deletion: two chromosomal breaks, resulting in the loss of an internal segment
interstitial deletion (results in a shorter than normal chromosome)
what is the human example of interstitial deletion?
WAGR syndrome
if a segment is deleted from both homologous chromosomes, it is a _______
deletion homozygote
_________- are repeated segments on a chromosome, can arise form unequal crossing over
duplications
unequal crossovers result in what two main categories?
partial duplication
partial deletion
an individual with one wildtype chromosome and one with duplicated material is a partial _________
duplication heterozygote
true/false: unequal crossover isn’t rare and occurs when homologs misalign during prophase I
false! it is rare!
what is an example of human duplications?
Williams-Beuren syndrome
in Williams-Beuren syndrome, what are the effects of the shortened partial deletion chromosome? the lengthened partial duplication chromosome?
shortened: causes the phenotypic effects in the disorder
lengthened: has no negative phenotypic effects
how do we detect deletions and duplications? two ways
using a microscope, can usually see them if they’re 100 000- 200 000 basepairs or more
look for unpaired loops
how/when do unpaired loops form?
form during the mismatch of homologous pairs during prophase I
when do chromosome inversions happen?
when two “sticky ends” join back to the broken chromosome, but in the wrong orientation
__________ inversion: beside the centromere
paracentric inversion (doesn’t include the centromere)
_________ inversion: around the centromere
pericentric inversion (includes the centromere)
_________ heterozygotes have one wildtype chromosome and one inverted chromosome
inversion heterozygotes
true/false: inversions usually only affect one member of the homologous pair
true!
________: has two centromeres
dicentric
_______: has no centromeres
acentric
during ___________, a dicentric bridge forms as the dicentric chromosome is pulling towards both poles of the cell (breaking it due to tension)
anaphase I
in a pericentric inversion, crossing over occurs…
inside the region of the inversion loop
inversions create _______ suppression
crossover suppression
when a chromosome breaks and the fragment reattaches to a different chromosome, or to a new spot on the same chromosome, ________ has occurred
translocation
________ heterozygotes have one wildtype chromosome and one altered chromosome
translocation
_________ translocation: reattachment to a new chromosome (a one-way event)
unbalanced
_________ translocation: two chromosome swap fragments with each other (a two-way event)
reciprocal
________ translocation (chromosome fusion): two nonhomologous chromosomes fuse together, with the loss of one of the centromeres
Robertsonian translocation
_____________: will move chromosomes I and IV to one poles, and II and III to the other pole
alternate segregation
________: will move chromosomes I and III to one pole, and chromosomes II and IV to the other
adjacent segregation
________ are associated with many types of cancer, and genomic instabilities
translocations
