lecture 4 Flashcards
when examining a karotype which blood cells do we usually look at
we look at the white blood cells because red blood cells do not have nuclei
centromere
a constriction in the chromosome involved in chromosome replication
(region of a chromosome that serves as a point of attachment for spindle fibers during cell division)
which arm is long and which is short
p = short arm
q = long arm
metacentric chromosome
type of chromosome where the centromere is located near the middle, dividing the chromosome into two arms of approximately equal length.
acrocentric chromosome
where the centromere is located near one end, resulting in one long arm and one short arm
in humans which chromosomes are acrocentric
13, 14, 15, 21 and 22
what order is information listed in the standard method when talking about chromosomes
- which chromosome
- which arm
- which band
- which sub-band
what does it mean by the ABO gene is on chromosome 9q34
the ABO blood gene is on the 4th sub band of the 3rd band on the long arm of chromosome 9
what is the standard description for a karotype
1) number of chromosomes
2) sex chromosomes
3) numerical abnormalities
4) structural abnormalities
what do you write for the sex chromosomes of men
XY
what do you write for the sex chromosomes of women
XX
list 5 different numerical chromosomal abnormalities
trisomy
tetrasomy
double trisomy
monosomy
polyploidy
Trisomy
three copies of a chromosome instead of 2
can occur in any chromosome but most common is trisomy 21 (down syndrome)
tetrasomy
four copies of a particular chromosome instead of 2
most common case is tetrasomy X, which involves four copies of the X chromosome in females
double trisomy (48,XXX, +21)
double trisomy refers to having an extra copy of two different chromosomes
in this case they have an extra X chromosome and an extra chromosome 21
monosomy
they have 45 chromosomes instead of 46
polyploidy
condition where the organism has more then 2 sets of chromosomes
triploidy
a cell that has an extra set of chromosomes
(69 chromosomes, three sets all together)
tetraploidy
extra 2 sets of chromosomes
(has 4 sets all together, 92)
more common to appear in leukemia cells
5 common chromosome abnormalities
down syndrome
patau syndrome
edward syndrome
turner syndrome
klinefelter syndrome
what is crucial when looking at structural abnormalities
has the person lost or gained any genetic material
pericentric inversion
an inversion that has gone round the centromere
paracentric inversion
chromosomal rearrangement that occurs within one arm of the chromosome (it does not involve the centromere)
people are usually fine
isochromosome
has two long arms instead of a long arm and a short arm
reciprocal translocation
exchange of genetic material where two arms have swapped over
result of a reciprocal translocation
the person is usually fine because it is a balanced rearrangement and most of the breaks are liking to happen in a non coding region
how common is down syndrome
1 in 700 births
what are common clinical issues down syndrome people may have
- developmental delays
- intestinal atresias
- epilepsy
- hypothyroidism
- deafness
- leukemia
nullisomic gamete
missing both copies of a particular chromosome pair.
lacks one entire chromosome pair out of the usual two sets of chromosomes.
what happens is a nullisomic gamete is fertilized with a normal gamete
resulting zygote would have one copy of the chromosome pair
would not give rise to a baby, does not implant or is miscarried very early
what is the chance of the child having down syndrome if the mother is carrying a chromosomal rearrangement
20-25%
what is the chance of the child having down syndrome if the father is carrying a chromosomal rearrangement
3-5%
Patau’s syndrome
also known as trisomy 13, extra chromosome 13
neonatal death
death of a newborn within the first 28 days of life
Patau syndrome results in
- holoprosencephaly ( a single small forebrain)
- cleft lip and palate
- congenital heart disease
Polydactyly: Extra fingers and/or toes
usually neonatal death or stillbirth
Edward syndrome other name
trisomy 18 (extra copy of chromosome 18)
affects of Edward’s syndrome
- growth retardation
- clenched hands
- rocker bottom feet
- congenital heart disease
- exomphalos (intestinal contents outside abdomen)
usually neonatal or stillborn
how common is Edward’s syndrome
1 in 3000 births
meiotic non dysjunction
when homologous chromosomes fail to separate properly during meiosis, leading to an imbalance of chromosomes in the resulting gametes.
can occur during either the first or second meiotic division
Turner’s syndrome
45, X
absence of one of the X chromosomes usually found in women
turner’s syndrome clinical features
- short stature
- ovaries do not develop
- webbed neck
- swollen feet and hands (peripheral lymphoedema)
Klinefelter syndrome
47, XXY
affects males, they have an extra X chromosome
clinical features of Klinefelter syndrome
- hypoganadism: underdeveloped testes
- infertility
- long limbs
- learning difficulties
risk of Klinfelter syndrome
1 in 1000 males
indications for chromosomal analysis
- multiple congenital anomalies
- ambiguous genitalia
- primary amenorrhea
- primary male infertility
5, recurrent miscarriages - significant unexplained developmental delay
- prognostic features in leukemia
Di George syndrome
also known as 22q11 deletion syndrome
1 in 4000 births
