Other Aberrations Flashcards
A _____ is an individual w/ 2 or more cell lines that were derived from a single zygote.
mosaic
About ____ of patients with trisomy 21 are mosaics w/ normal & trisomic cell lines.
1%
Mosaic arises after fertilization. In this case, the initial zygote has trisomy 21 and a normal cell line is produced at a subsequent mitosis by _____.
anaphase lag
T/F. Mosaic may also arise, albeit less frequent , when the initial zygote is normal & a trisomic cell line arises at a subsequent mitosis by non - disjunction. In this event, a cell line w/ monosomy 21 will also be produced, w/c will tend to be lost.
True.
The presence of the normal cell line tends to ameliorate the clinical picture, & if the abnormal cell line is confined to the gonad, _____ then an outwardly normal parent may have a high risk of producing abnormal children.
gonadal mosaic
A ____ is an individual with two cell lines that were derived from two separate zygotes.
chimaera
This could arise by the early fusion of fraternal twin zygotes, by double fertilization of the egg & a polar body or, more commonly, by exchange of haemopoietic stem cells in utero by dizygotic twins.
Chimaera
T/F. Chimaerism is not confirmed if a double contribution of maternal and paternal alleles can be demonstrated in the two cell lines.
False. Confirmed
Normally, each parent contributes one member of each pair of autosomes and one sex chromosome, but occasionally both homologues of an autosome are from one parent w/ loss of the corresponding homologue from the other parent. This can arise if the conception is trisomic for the homologue and one homologue is lost from the zygote by ____ at an early cell division to leave the 2 copies of the homologue that came from the same parent. This process is called ____.
anaphase lag; trisomic rescue
If the trisomy occured post-fertilization, _____ then occurs by loss of the third copy of that chromosome, _____ will result in the patient
trisomic rescue; uniparental disomy
If the trisomy resulted from non - disjunction at the second meiotic division, then the two homologues in the disomic gamete will be identical and ____ will be found in the patient after trisomic rescue
uniparental isodisomy
T/F. Uniparental disomy and isodisomy result in a abnormal karyotype, and can be detected by DNA marker analysis.
False. Normal karyotype
Where does the clinical consequence of uniparental disomy and isodisomy arise?
Genomic imprinting of certain chromosomal regions w/ consequent parent - specific expression of alleles in these regions.
Prader – Willi syndrome is usually caused by a paternal deletion of the _____, but occasional patients with the same clinical appearance have no deletion but have ____.
proximal long arm of chromosome 15; maternal uniparental disomy for chromosome 15
T/F. Uniparental isodisomy can also lead to homozygosity for mutant genes on the involved chromosome and so result in an autosomal recessive single - gene disorder in a child with only one parent being a carrier.
True
