Cytogenetics Flashcards
of chromosomes in human
46; 23 pairs; 22 pairs of autosomes (1-22 largest-smallest) and 1 pair of sex chromosomes
karyotype
3 elements: total # of chromosomes, sex chromosomes, any abnormalities; can refer to chromosome status - how many? which sex chromosomes? any abnormalities? can refer to pic of ind’s actual chromosomes
male w down syndrome
47 (extra chromosome 21) chromosomes, XY
female w turner syndrome
45 (missing X chromosome), X
male missing one chromosome 6
45, XY, -6
g banding
gives each chromosome arm unique combination of black, white, and grey bands; allows for detection of chromosome rearrangements; grow cells in culture and halt mitosis in metaphase when chrs are densest and easiest to see under a microscope
fluorescence in situ hybridization (FISH)
relies on the fact that complementary seqs bind to each other
probes
single stranded DNA mols that have been labelled w fluorescent molecule used by hybridization techniques
metaphase spread
when cells and nuclei burst and chromosomes spill out after dropping culture onto glass slides
aneuploidy
not having the “standard” # of chromosomes for your species (having wild type # of chromosomes = euploid)
polyploidy
having one or more extra full sets of chromosomes (ex: triploidy = having 3 full sets) occurs in 10% of spontaneous abortion in humans
aneusomy
increase or decrease in the # of a specific chromosomes (not entire sets as in polyploidy)
nullisomy
no copies of a specific chromosome
monosomy
1 copy of a specific chromosome (di, tri, tetra)
partial aneusomies
deletion and duplications that include a portion of a chromosome
chromosome nondisjunctions
leads to aneusomies; can happen as somatic mutation during mitosis - present in only a subset of the ind’s cells; mosaicism; increases w age (reduced ability to recombine during prometaphase I)
mosaicism
all people are mosaics because all people have somatic mutations
trisomy 21
only trisomy that produces viable offspring; other trisomies are usually lethal; in other organisms trisomies are viable (ex: Jimson weed)
polyploidy in plants
common; strawberries are hexaploid; commercially desirable: larger cells larger fruits, veggies, leaves; usually sterile w poorly developed seeds which makes them easier to eat
autopolyploidy
all chromosomes are from the same species; results from wholesale nondisjunction of all chromosomes or failure of the cell to split; 3 specific mechanisms*; sterility bc of unbalanced gametes
allopolyploidy
ind inherits chromosomes from 2 different species (species must be similar enough to each other for sperm and egg to be compatible); results from hybridization of gametes from 2 diff species
early mitotic nondisjunction
creates diploid cells that can undergo meiosis
euploid
having wild type # of chromosomes; non of us are completely euploid
centromere deletion
chromosome will be post during next cell division; transposable elements can cause deletions*
pseudodominance
ind loses dominant allele phenotypic characteristics reflects presence of recessive allele as only allele present
haploinsufficiency
one copy of gene is lost and causes abnormal phenotype bc one working copy of the gene cannot make enough of the protein
using deletions to map genes responsible for diseases
people w deletions in specific area = some have disease some don’t both narrow down location of disease causing mutation
displaced duplication
not side by side
reverse duplication
inverted duplication
duplication & new genes
possible for mutation to affect duplicate w/o harming org
insertion (nonreciprocal translocations)
piece of one chromosome is broken out and inserted into another chromosome
reciprocal translocations
2 chromosomes break and exchange pieces
balanced reciprocal translocation
no DNA lost; possible to have normal phenotype; can produce unbalanced gametes
unbalanced reciprocal translocation
DNA lost; possible but less likely to have normal phenotype
position effect
some genes expressed in specific order = moving one away from cluster may silence it; translocation can move normally active gene close to heterochromatic region = silencing the gene
Robertsonian translocations
result from fusion of 2 acrocentric chromosomes (13, 14, 15, 21); single chromosome; do not usually produce abnormal phenotypes* (so many copies of rRNA gene in acrocentric chrs you can afford to lose some); can result in trisomies bc cell recognizes RT as single chr
Rob(14q;21q)
one of the more common causes of down syndrome
pericentric
if inversion breakpoints lie on either side of centromere
paracentric
if both breakpoints lie w/i same chromosome arm
transposable elements
can cause inversions (balanced vs. unbalanced)
inversion
segment of chromosome is turned 180 degrees; balanced vs. unbalanced; position effects
inversion loop
in heterozygotes homologous chromosomes must form inversion loop during meiosis so all regions of chromosome can align properly
heterozygous pericentric inversion
result in reciprocal duplications/deletions*
ring chromosomes
lose material from both p and q arm then form a ring
