Week 10 - Chromosomal Abnormalities Flashcards
What is the long arm of a sub-metacentric chromosone called?
q arm
short = p arm
What is a metacentric chromosone?
centromere is in the centre
p and q arms are of equal length
eg human chromosones 1 and 3
What is an acrocentric chromosone?
short p arm can be deleted without harm
eg chromosone 14, 21, Y
What are autosomes?
chromosones 1-22
Where is this gene located?
11p15.5
chromosone 11
short arm
main band 1
sub-band 5
sub-sub band 5
(bands are numbered according to increasing distance from centromere)
What is a karyotype?
a description of a chromosone set
eg 46, XX = normal female
What syndrome does this individual have?
47, XX, +21
female with Down Syndrome
What is the karyotype for an individual with Turner Syndrome?
45, X
What is cri du chat syndrome?
an individual with the karyotype
46, XY (or XX), del(5p)
deletion of the short arm of chromosone 5
name comes from the characteristic cry of affected infants
What are the two main types of aneuploidy?
aneuploidy - abnormal number of chromosones
trisomy - presence of an extra chromosone
monosomy - absence of a chromosone
(polyploidy - presence of extra set(s) of chromosones)
Normal = 46
consequence is too little/too much protein produced as a result of the extra genes
How do aneuploidies arise?
non-disjunction
failure of sister chromatids to separate properly during cell division
can occur at meiosis I or meiosis II
What is a disomic gamete?
a gamate with two copies of a chromosone rather than one
if fertilised this gamate will give a trisomy individual
nullisomic gamate - no copies of a specific chromosone
What is Patau syndrome?
Trisomy 13
47, XY, +13
What are the consequences of males gaining an extra X chromosone?
karyotype - XXY
tall, infertile, possible poorly developed secondary sexual characteristics and slight reduction in IQ
Klinefelter syndrome
What is the number of inactive X chromosones in an individual with the karyotype XXX?
2
in female somatic cells only one randomly chosen X chromosone is active
regardless of number present only one X chromosone is active
What is an invasive method of diagnosing common aneuploidies prenatally?
amniocentesis and chromosonal analysis
usually definitive, 1% risk of miscarriage
Does an inversion of a chromosnone affect the health of the individual?
no medical problems
risk of loss/gain of material during recombinationbetween normal chromosone and chromosone with inversion
What is reciprocal translocation?
exchange of material between non-homologous chromosones
no net loss or gain of material
What kind of karyotypes do cancer cells have?
very abnormal
structural and numerical changes, aneuploidy is a ubiquitous feature
Why do sex chromosone abnormalities cause mild symtoms?
X chromosone inactivation
What is the ‘Philadelphia chromosone’?
a reciprocal translocation between chromosone 9 and 22
gives rise to fusion gene bcr-acl
asssociated with chronic myelogenous leukaemia
t(9;22)(q34;q11)
What is the effect of the BCR-ABL fusion gene created by the ‘Philadelphia translocation’?
ABL kinase is always switched on resulting in unregulated cell division leading to cancer
What is trisomy 18 also known as?
Edwards Syndrome
very severe condition, most babies born with trisomy 18 in every cell in their body will die before infancy
