Structural Chromosomal Abnormalities Flashcards
What are some examples of structural abnormalities?
Translocation Inversion Deletion Duplication Rings Robertsonian
What are the two types of translocational abnormalities?
Reciprocal and robertsonian
What is translocation?
Exchange of two segments between non homologous chromosomes
What is the main reason translocation takes place?
Inappropriate non-homologous end joining
What is non-homologous end joining?
DNA repair mechanism that repairs double stranded breaks by literally just sticking them back together
How is a derivative chromosome created?
Broken bits of chromosome being stuck back on the wrong chromosome
What is balanced translocation?
There is non-homologous end joining but because the net amount of DNA in a cell hasn’t changed, it doesnt matter
What is the philadelphia chromosome?
Derivative chromosome 22
What does the philadelphia chromosome cause?
The activation of the oncogene nature of the gene
Leads to types of leukaemia and myeloma
What is the philadelphia chromosome formed from?
Non-homologous end joining between a proto-onco gene on chromosome 9 and a gene on chromosome 22
How are unbalanced individuals produced?
Tetravalent structure formed instead of a bivalent structure
What is a tetravalent structure formed from?
Two normal chromosomes and two chromosomes that have undergone inappropriate non-homologous end joining
What do unbalanced individuals cause?
Essentially trisomic for one end of the chromosome and monosomic at the other end
What are the results of unbalanced reciprocal translocation?
May lead to miscarriage
Learning difficulties/physical difficulties
Very person-specific so clinical features vary
Where is the only place robertsonian translocation can happen?
With acrocentric chromosomes that carry specific sets of copies of rRNA