Chromosome Aberrations Flashcards
deletion
missing part of a chromosome
Cri du chat
human disorder due to missing part of the short arm of one copy of chromosome 5
terminal deletion
single break in the chromosome so the end is separated from the rest
an acentric fragment will be produced
acentric fragment
piece of chromosome that does not have a centromere
resulting from deletion
these will be lost during cell division
insterstitial deletion
a segment of the chromosome that is not at the end is deleted
requires 2 breaks and then the chromosome is resealed
an acentric fragment will be produced
compensation loop
created during synapsis in meiosis in heterozygous individuals (those with one normal chromosome and one chromosome with a deletion)
one of the chromosomes pokes out (the one without deletion) as this region doesn’t have a homologous region to synapse to
haploinsufficiency
single copy of gene is not enough to allow the wild-type phenotype to occur
pseudodominance
expression of normally recessive phenotype because their is no homologous allele due to deletion
effects of deltions
- acentric fragments are lost
- imbalance in the amount of gene products produced
- deletion of normal allele on one chromosome may allow the recessive allele on the homolog to be visible causing mutant
Normal: AB.CDEFG
Duplication: AB.CDEFDEF
Tandem
Normal: AB.CDEFG
Duplication: AB.CDEFFEDG
Reverse Tandem
Normal: AB.CDEFG
Duplication: AB.CDEFGDEF
Homobrachial Displaced
Normal: AB.CDEFG
Duplication: DEFAB.CDEFG
Heterobrachial Displaced
duplication
extra copies of a part of a chromosome
tandem duplication
the duplicated copy is next to the original with the same gene order
will form compensation loop
reverse tandem duplication
the duplicated segment is next to the original but in backwards order
displaced homobrachial
same arm
the duplicated segment is on the same arm of the chromosome but not next to the original
displaced heterobrachial
not adjacent to the original and on the other arm
unbalanced gene dosage
changes phenotype
ex. Bar eye mutation in drosophila - duplication leads to fewer eye facets and narrower shape
Susumu Ohno
duplications are essential to origin of new genes in a species
- one copy of each gene is essential to survival and therefore cannot accumulate mutation
- however the duplicated can and may develop a different function overtime which may become essential to the species as it evolves
inversions
segment of chromosome is removed, turned 180 degrees, and reinserted into chromosome
paracentric inversion
- inverted area does not include centromere
- doe not change arm ratio of chromosome
pericentric inversion
- inverted area does include centromere
- can alter arm ratio
synapsis of homolog when one has an inversion create a…
inversion loop