Cytogenetics 1 Flashcards
exam 2
short arm and goes up
p
long arm and goes down
q
centromere in the middle
metacentric
centromere in the upper part
submetacentric
centromere at the tip
acrocentric
exchange of material between two or more chromosomes
translocation
loss of material
deletion
gain of material
duplication
alteration within a chromosome
inversion
numbers stay at 46
structural
gain or loss of a chromosome–> number changes from 46
Numerical
trisomies that are compatible with life
13, 18, 21 and X/Y
Is a loss of sex chromosome compatible with life
yes
47, XX/XY, +21
Down
47, XX/XY, +18
Edwards
47, XX/XY, +13
Patau
small size, small head circumference - congenital heart defects - overlapping finger - rocker bottom feet - very poor prognosis, only 5% survive beyond 1 year
Edwards syndrome features
single palmar crease - sandal gap - small ear - nuchal skin fold - clinodactyly - hypotonia - hyperflexibility of joints
Downs’ syndrome: newborn features
intellectual disability - congenital heart disease gastrointestinal abnormalities -atlantoaxial instability -strabismus - thyroid abnormalities -leukemia
Downs syndrome: associated findings
scalp defects, microcephaly, micropthalmia, holoprosencephaly, clef lip and palate - CHD - polydactyly - renal anomalies - very poor prognosis
trisomy 13 features
sex chromosome changes (4)
(1) turner syndrome (2) klinefelter syndrome (3) 47, XYY (4) 47, XXX
only one X chromosome present no other X or Y
turner syndrome
1 in 2,00-2,500 female births - lymphedema in infancy - bicuspid aortic valve, coarctation of aorta - low posterior hairline, webbed neck, widely-spaced hypoplastic nipples-horshoe kidney -cubitous valvus of elbow
turner’s syndrome
45, X
turners ~50%
46, X abnormal X
turners syndrome
1 in 500 - 1,000 male births - tall stature, long limbs -learning differences - gynecomastia - small testicles - infertility due to hypogonadism with oligospermia/ azoospermia
klinefelter syndrome
two x chromosome and one small Y
klinefelter
- 1 in 1,000 female births -speech delay, IQ 10-15 points below siblings -increased risk for infertility - most offspring are chromosomally normal
47, XXX
- 1 in 1,000 male births - IQ 10-15 points below siblings - may be at increased risk for behavioral problems- impulsivity and emotional immaturity - most offspring are chromosomally normal
- risk of infertility issues
47, XYY
compensates for dosage difference between males and females
x- inactivation
is x inactivation reversible?
Yes!
steps involved in X-inactivation (3)
(1) Counting (2) Choice (3) cis inactivation
Counting
mechanism to assess how many X-chromosomes present
Choice
random if both chromosomes normal
Abnormal X
inactivated if has XIST
translocation between X and autosome
normal X inactivated
Unbalanced X translocation
Abnormal X inactivated
counting requires at least one x chromosome is
active
Cis inactivation spreads in
both directions
amount of genes that escape inactivation
15%
XIST locus in
Xq13
cis inactivation in different tissues
variable expression
single chromosome changes are most often
non-disjunction
Diploid
2 copies for every chromosome
haploid
1 copy of every chromosome
triploid
3 copies of every chromosome
cause of triploid (3)
(1) 2 sperms fertilizing 1 egg (2) sometimes found in prenatal analysis (3) frequently seen in missed abortion material
69, XXY
three copies of every chromosome
nondisjunction during meiosis gives rise to
trisomy in the conceptus
meiosis and nondisjunction can occur
with any chromosome not just 13, 18, 21 but conceptus may not be viable
what can occur during fetal development?
trisomic rescue
trisomic rescue
one of the extra chromosomes is lost
trisomic rescue can result in
uniparental disomy
heterodisomy; three different copies of a chromosome
isodosomy; two copies are the same but one is a new different copy
M1 Block
M2 Block
normal

- isodosomy
- heterodosomy
- ok
- ok
- uniparental disomy
- ok
- ok
which X gets inactivated if a fetus has a blananced X- autosome translocation
Normal X is inactivated
infant that presents with oral and/or facial clefts, microphtalamia, cutis aplasia and cardiac abnormalities
Patau