lecture 6 - analysis of chromosomal disorders 1 Flashcards
What a karyotype, what do the bands represent?
Regions of heterochromatin (less active) or euchromatin (more active) DNA
What do the dark bands of a stained chromosome represent?
Inactive DNA - heterochromatin
What do the light bands of a stained chromosome represent?
Active DNA - euchromatin
What are the 2 classifications of chromosome based on their centromere position?
Acrocentric, metacentric
What is an acrocentric chromosome?
Chromosome with the centromere near the end, so has a long and short arm
What is a metacentric chromosome?
Chromosome with a central centromere and 2 equally sized arms
What is a telomere?
A region of replicated material at the end of the arm of a chromosome
What is the name for the long arm of a chromosome?
q arm
What is the name for the short arm of a chromosome?
p arm
What technique is used to provide a genome-wide survey for imbalances?
Chromosomal microarray
What are the clinical indication for assessing chromosomal structure?
Abnormality of growth or development, intellectual disability, recurrent miscarriage, cancer investigation
What sex does Turner Syndrome affect?
Girls
What are the presentations of Turner Syndrome?
webbed neck, coarction of aorta, growth delay, amenorrhoea, short stature
What are the chromosomal causes of Turner Syndrome?
Missing X chromosome or structural abnormality to X chromosome
What is mosaic Turner Syndrome?
Abnormality where not all cells in the body are missing an X chromosome
Why is Turner Syndrome often mosaic?
Because the loss of an X chromosome is often post-zygotic (not a result of non-disjunction in meiosis) so some cells have X and some don’t
Why does Turner Syndrome cause abnormalities when females normally have one X inactivated anyway?
Because the inactivated X chromosome in normal females is only 80% inactivated, and the 20% of genes still expressed are important to normal function
Is Turner Syndrome recurrent for mothers?
No
What is the karyotype for Turner Syndrome?
45,X
What is the karyotype of Klinefelter Syndrome?
47,XXY
What are the presentations of Klinefelter Syndrome?
Reduced Testicular function, tall stature, low IQ
What is the cause of Klinefelter Syndrome?
Meiotic non-disjunction leading to an extra X chromosome
What is chromosomal non-disjunction?
Failure of homologous chromosome to seperate during meiosis 1 or 2
What is the karyotype for Down Syndrome?
47,XX,+21 (additional chromosome 21 - trisomy 21)
