Translocations Flashcards
Translocations can allow for up to ___% of the genome to be trisomic (depending on the region)
4%
Translocations can allow for up to ___% of the genome to be monosomic (depending on the region)
2%
In translocations it is always recommended to study the ________ chromosomes
parental
Frequency of Robertsonian translocations
1 in 800/1000 (part of the balanced 1in 500 risk)
Acrocentric p arms account for _____ % of the genome
2.2%
Acrocentric chromosome distal satellite p13 arms contain up to 300 copies of _______ genes responsible for organizing the nucleolus
rRNA
Acrocentric chromosome distal satellite p12 region is known as the _________ ______ and comes before the p13 rRNA region
satellite stalk
5 acrocentric chromosomes
13, 14, 15, 21 and 22
_______ satellite family at centromeres of 1, 9, 13, 14, 15, 21, 22 and Y
beta
A ________ translocation (1916) involves two acrocentric chromosomes at the centromere where the derivative p arms are largely lost and two copies of q arms are observed
Robersonian
_____ - _____ % of trisomy 21 are Robertsonian translocations
4-5%
Derivative 21 mostly involve D chromosomes ____, _____ and _____ as the G chromosomes ______ and _____ are not viable
D = 13, 14, 15
G = 21 and 22
Most (75%) Robertsonian translocations involving 13, 14 and 15 are _____ ______ but up to 25% can be _______
de novo -75%
familial - 25%
Segregation of Robertsonian translocations occurs in meiosis ______ and involves the trivalent formation
metaphase I
Adjacent or alternate segregation patterns result in normal and balanced translocations?
Alternate
Almost all DS inherited from a familial der(14;21) is _______ (paternal/maternal) in
origin from error in meiosis ________
maternal, meiosis I
der(14;21) carriers
Risk of fetus with translocation trisomy 21,
− maternal carrier _____% at amniocentesis, about _______% at term
15%
10-12%
der(14;21) carriers
Risk of fetus with translocation trisomy 21,
− Paternal carrier, <____%
<1%
der(14;21) carriers
Risk of UPD14?
<1/2% for both maternal and paternal
True or false? The rare der(21;21) carrier or isochromosome 21q has essentially no chance of a chromosomally normal conception.
True
The rare der(21;21) carrier or isochromosome 21q is mechanistically the result of an error in meiosis _________?
meiosis I
Trisomy 13 incidence in live births?
1 in 16,000
Trisomy 13 life expectancy?
1 year
Trisomy 13 phenotype?
heart defects
urinary malformations
* Dysmorphia:
- Polydactyly; clenched fist
- Small head and eyes
- Cleft lip/palate
- Rocker-bottom feet
– Holoprosencephally
