lecture 4

Question 1

when examining a karotype which blood cells do we usually look at

Answer 1

we look at the white blood cells because red blood cells do not have nuclei

Question 2

centromere

Answer 2

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)

Question 3

which arm is long and which is short

Answer 3

p = short arm
q = long arm

Question 4

metacentric chromosome

Answer 4

type of chromosome where the centromere is located near the middle, dividing the chromosome into two arms of approximately equal length.

Question 5

acrocentric chromosome

Answer 5

where the centromere is located near one end, resulting in one long arm and one short arm

Question 6

in humans which chromosomes are acrocentric

Answer 6

13, 14, 15, 21 and 22

Question 7

what order is information listed in the standard method when talking about chromosomes

Answer 7

• which chromosome
• which arm
• which band
• which sub-band

Question 8

what does it mean by the ABO gene is on chromosome 9q34

Answer 8

the ABO blood gene is on the 4th sub band of the 3rd band on the long arm of chromosome 9

Question 9

what is the standard description for a karotype

Answer 9

1) number of chromosomes
2) sex chromosomes
3) numerical abnormalities
4) structural abnormalities

Question 10

what do you write for the sex chromosomes of men

Answer 10

XY

Question 11

what do you write for the sex chromosomes of women

Answer 11

XX

Question 12

list 5 different numerical chromosomal abnormalities

Answer 12

trisomy
tetrasomy
double trisomy
monosomy
polyploidy

Question 13

Trisomy

Answer 13

three copies of a chromosome instead of 2

can occur in any chromosome but most common is trisomy 21 (down syndrome)

Question 14

tetrasomy

Answer 14

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

Question 15

double trisomy (48,XXX, +21)

Answer 15

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

Question 16

monosomy

Answer 16

they have 45 chromosomes instead of 46

Question 17

polyploidy

Answer 17

condition where the organism has more then 2 sets of chromosomes

Question 18

triploidy

Answer 18

a cell that has an extra set of chromosomes

(69 chromosomes, three sets all together)

Question 19

tetraploidy

Answer 19

extra 2 sets of chromosomes

(has 4 sets all together, 92)
more common to appear in leukemia cells

Question 20

5 common chromosome abnormalities

Answer 20

down syndrome
patau syndrome
edward syndrome
turner syndrome
klinefelter syndrome

Question 21

what is crucial when looking at structural abnormalities

Answer 21

has the person lost or gained any genetic material

Question 22

pericentric inversion

Answer 22

an inversion that has gone round the centromere

Question 23

paracentric inversion

Answer 23

chromosomal rearrangement that occurs within one arm of the chromosome (it does not involve the centromere)

people are usually fine

Question 24

isochromosome

Answer 24

has two long arms instead of a long arm and a short arm

Question 25

reciprocal translocation

Answer 25

exchange of genetic material where two arms have swapped over

Question 26

result of a reciprocal translocation

Answer 26

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

Question 27

how common is down syndrome

Answer 27

1 in 700 births

Question 28

what are common clinical issues down syndrome people may have

Answer 28

- developmental delays - intestinal atresias - epilepsy - hypothyroidism - deafness - leukemia

Question 29

nullisomic gamete

Answer 29

missing both copies of a particular chromosome pair. lacks one entire chromosome pair out of the usual two sets of chromosomes.

Question 30

what happens is a nullisomic gamete is fertilized with a normal gamete

Answer 30

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

Question 31

what is the chance of the child having down syndrome if the mother is carrying a chromosomal rearrangement

Answer 31

20-25%

Question 32

what is the chance of the child having down syndrome if the father is carrying a chromosomal rearrangement

Answer 32

3-5%

Question 33

Patau's syndrome

Answer 33

also known as trisomy 13, extra chromosome 13

Question 34

neonatal death

Answer 34

death of a newborn within the first 28 days of life

Question 35

Patau syndrome results in

Answer 35

- holoprosencephaly ( a single small forebrain) - cleft lip and palate - congenital heart disease Polydactyly: Extra fingers and/or toes usually neonatal death or stillbirth

Question 36

Edward syndrome other name

Answer 36

trisomy 18 (extra copy of chromosome 18)

Question 37

affects of Edward's syndrome

Answer 37

- growth retardation - clenched hands - rocker bottom feet - congenital heart disease - exomphalos (intestinal contents outside abdomen) usually neonatal or stillborn

Question 38

how common is Edward's syndrome

Answer 38

1 in 3000 births

Question 39

meiotic non dysjunction

Answer 39

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

Question 40

Turner's syndrome

Answer 40

45, X absence of one of the X chromosomes usually found in women

Question 41

turner's syndrome clinical features

Answer 41

- short stature - ovaries do not develop - webbed neck - swollen feet and hands (peripheral lymphoedema)

Question 42

Klinefelter syndrome

Answer 42

47, XXY affects males, they have an extra X chromosome

Question 43

clinical features of Klinefelter syndrome

Answer 43

- hypoganadism: underdeveloped testes - infertility - long limbs - learning difficulties

Question 44

risk of Klinfelter syndrome

Answer 44

1 in 1000 males

Question 45

indications for chromosomal analysis

Answer 45

1. multiple congenital anomalies 2. ambiguous genitalia 3. primary amenorrhea 4. primary male infertility 5, recurrent miscarriages 6. significant unexplained developmental delay 7. prognostic features in leukemia

Question 46

Di George syndrome

Answer 46

also known as 22q11 deletion syndrome 1 in 4000 births