Chromosomes and Disease Flashcards
week 2
what are the origins of abnormal karyotypes?
Error in meiosis and maternal age
errors in mitosis ( anaphase lag)
polyploidy
The heritable condition of possessing more than two complete sets of chromosomes.
Euploidy
The state of a cell or organism having one or more than one set of the same set of chromosomes, possibly excluding the sex-determining chromosomes
aneuploidy
a genetic disorder where the total number of chromosomes doesn’t equal 46
non- disjunction
homologous chromosomes that fail to separate in anaphase
what are the two classes of chromosome abnormalities?
Acquired (during embryogenesis in a subset of cells = mosaic
Constitutional (found in each cell of body)
What are the five main causes of chromosome abnormalities
Anaphase lag
Chromsome missegregation
Meiotic/ mitotic failure
dispermy
incorrect DNA repair
Anaphase Lag
One chromosome fails to migrate to pole of spindle
Lagging chromosome hence excluded from nuclei of daughter
Trisomy in 10, 15 or 16 is:
early lethal
Gross generic imbalances prevent embryonic tissues from developing correctly
Dosage compensation and an example
Evolutionary mechanism allowing altered gene doseage
genes on X-chromosome evolved so that normal development and cell function can take place with only one X per cell
Barr Bodies
inactive X chromosome that has become hyper-condensed.
Area of heterochromatin representing X chromosome. One X chromosome is randomly and permanently inactive during embryogenesis.
what are the four ways in which polyploidy can occur via meiotic/mitotic failure and Dispermy?
Complete non-disjunction
Error in gamete formation: Chromosome duplicated but cytoplasm and cell as whole fail to divide into daughter cells.
Error in early mitotic cell division: chromosomes duplicate but cytokinesis does not occur.
Errors at fertilization (dispermy): simultaneous fertilization of haploid egg by two haploid sperm = triploid.
What are the two main types of chromsome inversion?
Pericentric and Paracentric
what are the two types of translocations?
Reciprocal and insertion
Philadelpiha Chromosome
90% of patients with Chronic Myelogenous Leukemia
BCR (from Ch-22) fuses with kinase ABL from (Ch-9) = uncontrolled division.
Roberson Translocations
Centric fusion of Ch 13 and 14 = end – end fusion of acrocentric chromosomes (centromere not central).
Normal phenotype as no loss/gain of material
Increased Risk of abnormal child or spontaneous pregnancy loss.
What is Uniparental Disomy and what two events are needed for it to occur?
Inheritance of 2 chromosomes or chromones parts from SAME parents
Due to simultaneous occurrence of two rare events:
Simultaneous non disjunction in sperm AND egg
Trisomy followed by chromosome loss.
What are the symptoms of UPD Prader-Willi Syndrome and what chromosome is affeceted?
Low muscle tone, short stature, incomplete sexual development
Cognitive disabilities, behavioral problems, chronic feeling of hunger = excessive eating and life-threatening obesity
paternal Ch 15g11-q13 lost
How can you tell if nondisjunction occurred in meiosis I or meiosis II?
I= three chromosomes, Non Identical
II- three chromosomes, 2 Identical
Does Pericentric or Paracentric include the centromere in inversion?
Pericentric
triploid vs trisomic?
Triploid= extra SET of chromosomes
Triploid = extra copy of ONE chromosome
What does anaphase lag often result in?
euploidy and monomsy
Describe the ouctome of meiosis I vs Meiosis II errors in Non-disjunction
Meiosis I errors
all gametes abnormal,
50% have trisomy and non-identical,
50% monosomy
Meiosis II errors
50% abnormal,
1 with trisomy, identical
1 monosomy
dispermy
simultaneous fertilsation of haploid egg by 2 haploid sperm = triploidy
