Chromosome Abnormalities Flashcards
Describe the process of GBanding staining and what it shows.
Metaphase chromosomes are exposed to trypsin which digests proteins, and then stained with a romanwaski type dye, the dark bands are known as G+ve bands, which are AT rich and therefore gene poor, the light bands are known as G-ve bands which are GC rich and therefore gene rich
Give some reasons for performing cytogenetic analysis.
For prenatal diagnosis, to assess future reproductive risks, to aloow for better clinical management, and for accurate diagnosis of clinical problems (eg accounting for a phenotype)
What are the two methods of obtaining chromosomes for a prenatal diagnosis?
Chronic villus sampling, which can be performed at 11-12 weeks with a 1.2% risk of miscarriage, and aminocentris, which can be performed after 15 weeks with a 0.8% miscarriage risk.
What is an aneuploidy?
Loss or gain of whole chromosomes
What are the possible causes of aneuploidy?
It can originate from non-disjunction at a meiotic division, or a mitotic division (which leads to mosaicism) forming one gamete with a missing chromosome and one with an extra chromosome.
What is the most common cause of polyploidy?
Polyspermy (when more than one eggs fertilise a sperm)
Give three examples of trisomys
Down Syndrome (trisomy 21) patau syndrome (trisomy 13) and edwards syndrome (trisomy 18)
What is mosacism?
Presence of two or more cell lines in the body
What is uniparental disomy?
The presence of homologus chromosomes from one parent
What is karotyping?
Metaphase chromosomes that are sorted, paired up and grouped together, a systematic sorting of chromosomes that can be used to detect abnormalities.
What is the affect of non-disjunction during meiosis I?
Two trisomys and two monosomy cells
What is the affect of non-disjunction during meiosis II?
1 trisomy, 1 monosomy and 2 normal cells
What is the problem in turner syndrome?
Monosomy X chromosome
Why is a monosomy of the X chromosome a problem?
As there are two psuedoautosomal regions in the X and y chromosome, which contain the genes such as the SHOX gene that is associated with short stature.
What are the different origins of Uni Parental Disomy?
Trisomy rescue, monosomy rescue, mitotic error, gamete complementarity.
What factor determines moscaism?
Non dyjunction in mitosis, if it happens at first mitotic division there will be a non-mosaic karyotype, if it occurs after this there will be a mosaic karyotype.
What is non dysjunction and what might cause it?
A different number of chromosomes being left in a cell in either mitotic or meiotic cell division, may be caused by anaphase lag, where chromosomes are left behind in cell division possibility due to defects in spindle function and attachment to chromosomes.
What is a reciprocal translocation ?
Two breaks in chromosomes, and the different parts on chromosomes swap places.
What are the different segregation types in reciprocal translocations?
3:1 non disjunction, 4:0 non-disjunction, alternate and adjacent 1 and adjacent 2.
What is a robertsoian translocation?
Where two acrocentric chromosomes (13,14,15,21,22) fuse together.
What are the risks associated with robertsonian translocation?
Aneuploidy risk
What are the two types of chromosome deletions?
Terminal, at the ends of chromosomes, and instial within the body of chromosomes
