Genetics 2 Flashcards
In notes how are the short arm and long arm of chromosomes written as?
p = short arm and q = long arm
What is an acrocentric chromosome? and what chromosomes are acrocentric?
Chromosomes what don’t really have a short arm. These are chromosomes 13, 14, 15, 21 and 22
What is balanced chromosome rearrangement?
Where all chromosomal material is present but it just isn’t in the correct place
What is unbalanced chromosomal rearrangement
Extra or missing chromosomal material, usually 1 or 3 copies of some of the genome.
What is aneuploidy?
A whole extra chromosome or a missing chromsome
What is 47 XY + 21
A boy who has trisomy 21 which results in down syndrome. The 47 means 47 chromosomes
What is 47 XY + 18
A boy who has trisomy 18 resulting in Edward syndrome
What is 47 XX + 13
A girl who has trisomy 13 resulting in Patau syndrome
What are some of the rapid prenatal diagnosis of genetic disorders
Interphase chromosome counting using FISH (fluorescence In Situ Hybridisation) or comparative genome hybridisation
What is 45 X
A girl with turner syndrome
What aneuploidy’s are better tolerated?
X chromosome aneuploidy due to X inactivation
Describe chromosomal insertions
This is a genetic mutation where part of one chromosome is cut out and gets inserted into another chromosome. Only symptomatic if it cuts through a gene.
What is Robertsonian Translocation
When two acrocentric chromosomes are stuck end to end. (look at an image)
What can result from Robertsonian translocation?
An increased risk of trisomy in pregnancy (50%)
What is 46 XY, der (14;21) + 21
A boy with 46 chromosomes with an inherited (der = derived) robertsonian translocation where an chromosome 21 joined onto chromosome 14 and counted as 1 whole chromosome. Therefore he has three 21 chromosomes worth of genetic material.
What is a reciprocal translocation
The exchange of two acentric fragments (chromosome lacking centromere) and this can occur with any autosomal chromosmes
Explain 46, XX, t(12;17)(p13;p13)
A woman with a translocation between chromosomes 12 and 17. At the short arm position 13 on both.
Explain 46, XY, der(17)t(12;17)(p13;p13)mat
A son who inherited chromosme 17 which has a translocation from chromosme 12 on the short arm at position 13.
What are the reproductive risks with reciprocal translocations
50% normal/balanced and 50% unbalanced. Unbalanced results in miscarriage (large segments) or dysmorphic delayed child (small segments)
What is a Philadelphia chromosome?
This is a reciprocal translocation between chromosomes 9 and 22 that can happen to anyone
What is the clinical significance of philadelphia chromosome
95% of patients with chronic myeloid leukaemia have this genetic mutation
What are some single chromosome mutations?
- Deletion.
- Duplication.
- Inversion
