Chromosome Syndromes Flashcards
Define Non-Dysjunction
Process of mis-division during meiosis & mitosis that brings about Aneuploidy in a cell.
Define Aneuploidy
An abnormal number of chromosomes in a cell.
Define Chromatin
Unwound Chromosome, ready for meiosis or mitosis.
Define Homologous pair of Chromosomes
A pair of chromosomes that contain the same genes but different alleles due to one being paternal and the other maternal.
Define centrosomes
An organelle near the nucleus that contains centrioles that forms the spindle fibres during cell division. (Also replicates like chromosomes before division)
What occurs in Interphase?
Homologous chromosomes replicate and are attached together by centromere. Organelles (centrosomes) also replicate.
What occurs during Prophase l?
Nuclear envelope disappears and spindle fibres form, homologous pairs line up and genetic recombination occurs.
What occurs during Metaphase l?
Spindle fibres attach to kinetochore (complex of proteins associated with centromere) of each chromosome.
What occurs during Anaphase l?
Just the homologous pairs separate from eachother (stay attached to replicate by centromere). Move to opposite pole of the cell.
What occurs during Telophase l?
The microtubules (spindle fibres) disassemble. Cytokinesis occurs (cytoplasm splits). Nuclear envelope forms again. Each of the two cells has half the number of chromosomes, still attached by centromere.
What occurs in Prophase ll?
Nuclear envelope disintegrates again. Centrosomes push apart in separate directions to form spindles.
What occurs during Metaphase ll?
Spindle fibres attach to centromeres. The chromosomes line up.
What occurs in Anaphase ll?
The spindle fibres splits the sister chromatids from the centromere to opposite poles = single chromosomes.
Define Uniparental disomy
2 copies of a chromosome come from same parent instead of one from each (maternal & paternal).
Describe the symptoms of Down’s Syndrome (Trisomy 21).
Hypotonic (floppy when baby) Poor reflexes Joints are hyper flexible Pelvic dysplasia Flat face Small ears Large tongue Simian Crease (single crease down palm)
What’s the risk of incidence of Down’s?
1/600-1/700
What’s the percentage risk for Down’s?
94% regular
- 5% translocation from 13,15,21
- 5% mosaic
Describe the symptoms of Edward’s Syndrome.
Feeble foetal activity Pelvic dysplasia "Rocker bottom" feet Neurological disorders Survive up to 2 years Maximum
What’s the risk of incidence in Edward’s syndrome?
1/3000-1/4000 live births
3 females: 1 male
What’s the life expectancy of a patient with Edward’s syndrome?
3-6 months unless mosaic
What’s the percentage risk of Edward’s syndrome?
90% regular
10% mosaic
Describe the symptoms of Patau’s Syndrome.
Severe neurological deficiencies Cardiac abnormality Retinal dysplasia Severe cleft lip and palate Deafness
What’s the risk of incidence for Patau’s syndrome?
1/5000 live births
What’s the percentage risk of Patau’s syndrome?
75% regular
20% translocation
5% mosaic
Name the other non-dysjunctions
Trisomy 16- lethal, spontaneous abortion at 13 weeks
Trisomy 8- very rare, lethal unless mosaic
Trisomy 9- very rare, majority die in early post natal
What is Turners syndrome?
Monosomy X (X inactivation)
Describe the symptoms of Turner’s syndrome
Short stature Lack of secondary sexual characteristics Infertile Webbed neck Variable IQ Can be colourblind
What’s the risk of incidence of Turner’s syndrome?
1/4000 live female births
List the prenatal diagnostic methods for chromosomal disorders
Amniocentesis Chronic villus biopsy IVF/ pre implantation diagnosis Bart's test- maternal blood sample, testing for proteins Mucosal membrane scan Colourblindness as a marker
What’s the percentage of sex chromosome abnormalities?
70% paternal
30% maternal
What’s the percentage of autosomal abnormalities?
90% maternal
10% paternal
