Abnormalities of chromosome structure Flashcards
(50 cards)
What are the two types of structural chromosome abnormalities?
Unbalanced and balanced
Unbalanced abnormalities cause a gain or loss of chromosomal material, while balanced do not.
What causes chromosome breakage during meiosis or mitosis?
Improper alignment of homologous chromosomes or harmful agents called clastogens
Clastogens include ionizing radiation, some viral infections, and certain chemicals.
What is a translocation?
The interchange of genetic material between nonhomologous chromosomes
What are the two basic types of translocations?
Reciprocal and Robertsonian
What happens in a reciprocal translocation?
Breaks occur in two different chromosomes and material is mutually exchanged.
What is a derivative chromosome?
The resulting chromosomes from a reciprocal translocation
What is the prevalence of balanced translocations in humans?
1 in every 500 to 1000 individuals
What is a common characteristic of the offspring of a carrier of a reciprocal translocation?
They can be normal, carry the translocation, or have duplications and deletions of genetic material.
What is a Robertsonian translocation?
The short arms of two nonhomologous chromosomes are lost and the long arms fuse at the centromere.
Which chromosomes are involved in Robertsonian translocations?
Acrocentric chromosomes: 13, 14, 15, 21, and 22
What is a terminal deletion?
A deletion caused by a single break that includes the chromosome’s tip.
What is an interstitial deletion?
A deletion resulting from two breaks where the material between the breaks is lost.
What are microdeletion syndromes?
Syndromes caused by small deletions that are often too small to be observed microscopically.
What is Prader–Willi syndrome?
A microdeletion syndrome caused by a deletion of chromosome 15q11-q13.
What is the inheritance difference between Prader–Willi syndrome and Angelman syndrome?
Prader–Willi results from a paternal deletion, while Angelman results from a maternal deletion.
What characterizes Williams syndrome?
Mild intellectual disability, supravalvular aortic stenosis, and characteristic facial features.
What gene is associated with Williams syndrome?
The elastin gene (ELN)
What is the significance of high-resolution banding techniques?
They allow for the detection of small deletions that were previously undetectable.
What types of genetic alterations can produce contiguous gene syndromes?
Microdeletions and microduplications.
Contiguous gene syndromes involve the deletion or duplication of adjacent genes, leading to specific phenotypic outcomes.
What is the significance of low-copy repeats in microdeletion syndromes?
They promote unequal crossing over, which can result in duplications and deletions of chromosomal regions.
Low-copy repeats are sequences that can lead to genomic instability during meiosis.
What are common symptoms of DiGeorge sequence?
- Structural or functional defects of the thymus
- Conotruncal heart defects
- Hypoparathyroidism
- Secondary hypocalcemia
DiGeorge sequence is caused by abnormal migration of neural crest cells during embryonic development.
What is the most common human microdeletion syndrome?
22q11.2 deletion syndrome.
This syndrome is associated with DiGeorge sequence and velocardiofacial syndrome and has a prevalence of 1 in 3000 to 4000 live births.
What gene is implicated in the 22q11.2 deletion syndrome?
TBX1.
The TBX1 gene encodes a transcription factor crucial for the development of facial structures, thymus, and heart.
What is uniparental disomy?
A condition in which one parent contributes two copies of a chromosome while the other parent contributes none.
This can lead to genetic diseases due to the absence of genes from one parent, particularly in imprinted regions.
