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
Does crossing over occur in inversion?
crossing over still occurs in an inversion lopp, but recombinant products are inviable
duplication and deletion result
dicentric bridges
- common in anaphase I when crossover occurs in a paracentric inversion loop
- occur when a chromosome has 2 centromeres
What leads to speciation?
Inversions
- individuals who are homozygous for either the original or the inverted produce more viable gametes than the heterozygote.
- this favors both extremes leading to disruptive selection
Evoutionary significance of inversion
- suppress crossover as the result are often not viable
- may lead to speciation
reciprocal translocation
two nonhomologous chromosome exchange are or parts of arms
there is no gain or loss of DNA
non-reciprocal translocation
a segment from one chromosome is moved to a nonhomologous chromosome
no overt gain or loss of DNA
Robertsonian translocations
two telocentric/nearly telocentric chomosomes combine to make one large, more metacentric chromosome
lose a bit of DNA that is not usually noticeable
isochromosome
two chromosomes joined are homologs
An individual who is a translocation carrier produces…
half viable gametes
half non-viable gametes
An example of robertsonian translocation
familial down syndrome
joining of chromosome 14 and 21 or compound chromosome of 21
The individual with familial down syndrome has…
46 chromosomes
3 copies of information from chromosome 21
The parent with robertsonian translocation has…
45 chromsomes
normal phenotype
2 copies of chromosome 21
Chronic Myelogenous Leukemia
fatal, uncontrolled replication of myeloid stem cells
reciprocal translocation involving chromosome 9 and 22 results in fusion of 2 oncogenes whose protein product causes uncontrolled replication
ex of impact of reciprocal translocation
Burkitt’s Lymphoma
abnormal function of B cells
reciprocal translocation between 8 and 14 places c-myc next to an enhancer which normally stimulates production of immunoglobin
position effect
same genes are present but chromosomal location alters the phenotype
