Chromosomal Structural Abnormalities Flashcards
(28 cards)
What is an isochromosome?
A duplication of a single chromosome’slong arm and loss of its short arm.
What is a Robertsonian translocation?
Fusion of the king arms of two different chromosomes with loss of each chromosomes short arms.
What two causes can result in a chromosomal deletion?
1) double stranded breakage and subsequent loss of a acentric fragment
2) unequal crossing over between misaligned homologues
What disease does a chromosomal deletion of of the PMP22 gene result in?
HNLPP ( the chromosome that got the duplicated gene leads to CMT)
What disease results from a deletion of part of chromosome 5’s p region and how is this deletion acquired?
Cri-du-chat is mostly due to sporadic cases, but about 10% are due to parental translocations.
Which of the following is not a symptom of cri-du-chat? Moderate to severe mental retardation Microencephaly Hypertelorism Epicanthal folds Low set ears Heart defects Renal anomalies Childhood death likely Low IQ in adults
Renal anomalies are seen in Turner syndrome
True or false: the genes in chrom 5p that’s result in cri-du-chat symptoms when deleted are unknown.
False: many of the genes responsible for the symptoms are known.
What syndrome does a deletion in chrom (4)(p16) result in and how does this deletion come about?
Wolf-Hirschhorn syndrome results mostly from sporadic cases, bit about 10% are a consequence of parental translocations.
Which of he following is not a symptom of Wolf-Hirschhorn syndrome? Mental retardation Growth retardation Hypertelorism Long protruding forehead Cleft lip and palate Broad nasal bridge Microcephaly Heart defects Seizures
Long protruding foreheads are seen in Patau syndrome (trisomy 13)
What is the problem that deletion or insertion mutations cause?
It can result in a partial trisomy.
What leads to a duplication mutation?
Unequal crossing over between misaligned homologues.
What results in an insertion mutation?
Breakage and subsequent insertion of an acentric fragment into another chromosome or itself in a non-adjacent area.
What structure is formed when homologues line up during metaphase if one homologue has an inversion mutation?
Inversion loop
True or false: paracentric inversions cannot be detected with CGH hybridization; banding or FISH must be used.
True
True or false: most inversion mutations are detected at birth.
False: inversion mutations usually do not result in viable offspring due to an imbalance in genes.
True or false: pericentric inversions do not result in gene duplications or deletion a on the chromosomes that underwent crossing over.
False
True or false: crossing over outside of inversions do not result in unbalanced genes.
True
Define translocation and the two types of it.
Exchange of chromosome segments between two (usually) nonhomologous chromosomes.
Reciprocal translocation: exchange of DNA between Nonhomologous chromsomes
Robertsonian translocation: fusion of two acrocentric chromosomes.
True or false: Translocations usually result in a balanced chromosome complement.
True
Usual segregation of translocation chromosomes is in the ratio of __:__, but sometimes it can be __:__, which produces ____ (rarely) or _____.
2:1
3:1
Monosomy
Trisomy
3:1 segregation is seen in 5-20% of sperm (frequency depending on translocation present)
Human Robertsonian translocations occur between which acrocentric chromosome?
13,14, 15, 21, 22
Why is the loss of short arms in Robertsonian translocations tolerated?
Because most of the DNA in the short arms is redundant in the genome.
What are the three most common Robertsonian translocations?
rob(13;14) ~33%
rob(14;21) ~30% (produces down syndrome)
rob(21;21) ~17% (aka an isosomal chromosome)
True or false: During the combination of a normal gamete plus a gamete with a Robertsonian translocation, the chromosome number will be normal (46) and the genes will be balanced.
False: the chromosome number will be 45.
