Structural Aberrations Flashcards
The 5 types of structural aberrations
Duplication, deletion, inversion, translocation, fragile sites
This usually arises from breaks in the chromosome
Structural aberrations
This is where a part of the genetic material is present more than once in the genome
Duplication
Give a cause of duplication
Unequal crossing over or errors during replication
What is the cause of the bar-eyed (bar-shaped eyes) mutation in drosophila?
Due to x-linked duplication in the bar gene
This reduces the number of facets in the eye of the drosophila
Bar mutation
This is the phenomenon where the chromosomal environment can have an effect on the expression of the specific gene
Position effect
This is where the phenotype of a gene is altered by changes in the position or chromosomal environment of the gene
Position effect
What do you call the normal gene in drosophila?
Wild type
______ crossing over produces bar and double-bar mutations
Unequal
What are the 2 types of deletion?
Terminal, interstitial
In prophase 1 during structural aberrations, the normal chromosome must ____ in order for the homologous sequences to align
Loop out
This is a disorder due to the deletion of a p-arm at chromosome 5, characterized by a high pitch cat-like cry, intellectual disability, delayed development, microcephaly, hypotonia, widely set eyes, low set ears, small jaw, rounded face, and a heart defect
Cri du chat syndrome
This is caused by a deletion of a section on the p-arm at chromosome 4 and is characterized by broad flat nasal bridge, high forehead, short philtrum, microgmathia, poorly formed ears, eyes are spaced and may be protruding, asymmetrical facial features and microcephaly, delayed growth, intellectual disability, and seizures
Wolf-hirschhorn syndrome
Deletion on the long arm at chromosome 15, feeding difficulty at early age, but becoming obese after 1 yr, mild to moderate mental retardation
Prader-willi syndrome
This is an aberration where it is turned 180 degrees within the chromosome
Inversions
What are the types of inversion?
Paracentric, pericentric
What does inversions result to?
Reduced fertility
In _______, the chromosomes form an inversion loop which allows the homologous sequences to align
Prophase 1
A type of inversion where the centromere is not included
Paracentric
A type of inversion where the centromere is included
Pericentric
What is present in a paracentric inversion?
Bridge formation and breakage effect
1 normal gene sequence, 1 inverted segment
Inversion heterozygote
Movement of a chromosome segment into a new location in the genome
Translocation
3 types of translocation
Nonreciprocal intrachromosomal translocation, nonreciprocal interchromosomal translocation, reciprocal interchromosomal translocation
Translocation that occurs in the same chromosome
Nonreciprocal intrachromosomal translocation
Translocation occurs between one of the chromatid of non homologous chromosomes
Nonreciprocal interchromosomal translocation
Translocation where a pair of non homologous chromosomes are both affected
Reciprocal interchromosomal translocation
Non-homologous chromosomes are not suppose to _____ genes
Share
This results from a reciprocal translocation where the configuration forms a tetravalent
Tetravalent configuration
2 types of disjunction in reciprocal translocation
Adjacent and alternate
This is defined by the fusion of the long arms of 2 acrocentric chromosomes near their centromeric region
Robertsonian chromosome translocation
This occurs because of robertsonian translocation
Translocation down syndrome
These are chromosomal regions susceptible to gaps or breaks
Fragile sites
How many fragile sites in the human genome?
120 and is associated with mental retardation
This is a common form of mental retardation, affects 1/1250 males and 1/2500 females, behaves as a dominant trait, shows variable expressibility, males show long and narrow faces with protruding chins, enlarged ears, increase in testicular size
Fragile-x syndrome/martin bell syndrome
What is variable expressibility?
Only 30% of fragile x females are retarded but 80% of males are retarded
What gene spans the fragile site?
FMR-1 gene
What sequence of three nucleotides is repeated many times in the fragile-x syndrome gene?
CGG
(Fragile-x syndrome) 6-54 cgg repeats
Normal
(Fragile-x syndrome) more than 200 cgg repeats
Affected
(Fragile-x syndrome) 55-200 cgg repeats
Carrier
This is when heritable disorders exhibit a progressively early age of onset and increased severity of disorder in each successive generation
Genetic anticipation
Fragile-x syndrome is more common in?
Men
This is characterized by long face, large jaw, large prominent ears, high arched palate, microcephaly, autism, adhd, prader-willi phenotype, intellectual disability, broad forehead
Fragile-x syndrome
