MGD 10 - chromosomal abnormalities

Question 1

what is karyotyping?

Answer 1

pairing of metaphase chromosomes for analysis by:
G-banding (AT tich regions dark)
C-banding (centromeres)
Q-banding (fluorescence)

Question 2

what is the standard way of reporting results?

Answer 2

number of chromosomes, sex, +/- chromosomes

Question 3

what are the referral reasons for karryotyping?

Answer 3

constitutional: recurrent miscarriage, infertility, altered development, prenatal diagnosis
acquired: leukaemia, lymphoma, myeloma, solid tumours, muscular dystrophy (MDS)

Question 4

what is aneuploidy?

Answer 4

abnormal number of chromosomes

e.g. an extra chromosome - 45/47 and not 46

Question 5

what is polyploidy?

Answer 5

an entire new set of chromosomes (haploid become triploid)
(XXX, 69 chromosomes)
can form gamete with extra chromosome e.g. down syndrome (trisomy)

Question 6

what is monosomy?

Answer 6

forming gamete with missing chromosome (monosomy - only 1 set) e.g. Turner’s syndrome (don’t survive)

Question 7

what can aneuploidy be caused by?

Answer 7

a non-disjunction event during meiosis or early mitosis (mosaicism - 2nd cell population in an individual - cases where mother isn’t mother of child)
can also be result of anaphase lag (1 chromatid in mitosis fail to attach to spindle)

Question 8

what is polyspermy?

Answer 8

the most common cause of polyploidy (triploidy, tetraploidy) - more chromosomes than normal
e.g. fertilised by multiple sperm

Question 9

what is uniparental disomy?

Answer 9

when a chromosome pair originates from a single parent, made possible through trisomy rescue (trisomy zygote looses 1 copy of chromosome to become diploid - normal), monosomy rescue or polyspermy

Question 10

what is reciprocal translocation?

Answer 10

chromosome fragments translocate reciprocally (exchange of materials between non-homologous pairs) from 1 chromosome to another
depending on the segregation pattern during meiosis

Question 11

how is the offspring produced from reciprocal translocation like?

Answer 11

the offspring can be balanced (change doesn’t cause any missing info), or unbalanced (change causes missing / extra genetic info) depending on which chromosome pair you inherit
associate with specific disease e.g. CML/AML

Question 12

what is robertsonian translocation

Answer 12

a translocation involving the fusion of the q arms (long) of 2 different acrocentric chromosomes, during which the smaller p arm fusion often becomes lost
balanced (45,XX) or unbalanced (46,XX,+21)

Question 13

why can the p arms be disposable in robertsonian translocation?

Answer 13

small arms code for some rRNA elements which are disposable as they are repeated throughout the genome (whole human genetic info)