Week 6- Chromosomal Abnormality Flashcards
How is DNA formed into chromosomes?
It is wrapped around histone proteins to form nucleosomes and these coil to form chromatin fibers which condense to form a chromosome
What are G dark bands on chromosomes?
Areas of the chromosome that are darker, tightly bound and DNA poor. G light bands are the opposite of this (loosely bound, light and DNA rich)
What are the p and q arms of chromosomes?
P= short arm Q= long arm
How is a normal karyotype written?
46, XX
How is a karyotype with a translocation written?
46, XX, t(5;10), (q 13.4; q 11.2)
t= translocation
second bracket= location of the translocation
How is a karyotype with a deletion written?
46, XX, del (5), (q 21, q 23)
How is a karyotype with monosomy written?
46, XX, -7
Loss of chromosome 7
How is a karyotype with trisomy written?
47, XX +8
Gain or whole chromosome
What is a haploinsufficient gene?
Needs to be present on both chromosomes to be expressed
What is an imprinted gene?
A gene present only on maternal or paternal not both
What is the aim of mitosis?
To create genetically identical daughter cells for growth and repair or to replace exhausted cells (2n goes to 2n)
What is the aim of meiosis?
To achieve reduction from diploid to haploid so there can genetic variation (2n goes to n)
What 2 processes does meiosis achieve?
Random assortment of homologues
Genetic recombination
What is the main risk of the maternal age effect?
Non disjunction at meiosis
At meiosis 1: 2 gametes have trisomy, 2 have monosomy
At meiosis 2: 2 gametes are normal, 1 has trisomy, 1 has monosomy
Why may cells in female meiosis be more vulnerable than cells in male meiosis?
Female meiosis is paused in utero till puberty
What syndrome arises due to trisomy 13?
Patau’s
What syndrome arises due to trisomy 18?
Edward’s
What syndrome arises due to trisomy 21?
Down’s
Which trisomy most often causes miscarriage?
16
What is quantitative fluorescence PCR? What are the different results and what do they indicate
When polymorphisms are amplified and quantified (everyone has different ones)
A= uninformative B= 1:1 (normal) C= 1:1:1 (trisomy at meiosis I) D= 1:2 (trisomy at meiosis II)
What are some risks associated with the paternal age effect?
Inversions, deletions, translocation
What is usually more tolerated out or trisomy and monosomy?
Trisomy
What are observable features in those with William’s syndrome?
Very social personality, long philtrum, arched eyebrows, short+upturned nose
What is array comparative genome hybridization used for and how is it carried out?
It is a genome wide scan for genetic imbalance carried out by hybridizing DNA after labeling it w colors, then a computer array analyzing colors that overlap to identify imbalances
