Chromosome Abnormalities

Question 1

what is the P arm of chromosome?

Answer 1

smaller (petite) arm

Question 2

what is the Q arm of chromosome?

Answer 2

longer arm

Question 3

how are chromosomes ordered on a karyotype?

Answer 3

largest to smallest

Question 4

how do scientists differentiate between chromosomes?

Answer 4

size, banding pattern, centromere position

Question 5

what is a metacentric chromosome?

Answer 5

centromere is roughly in the centre of the chromosome so p and q arms a basically same length. e.g. chromosome 1

Question 6

what is a submetacentric chromosome?

Answer 6

centromere is off centre so p arm and q arm are easily identifiable. e.g. X chromosome

Question 7

what is an acrocentric chromosome

Answer 7

centromere is located at one end of the chromosome so p arm is super short or essentially non-existent e.g. chromosome 21

Question 8

what is the difference between a normal female and a normal male karyotype?

Answer 8

normal male has xy and normal female has xx

Question 9

what is the resolution of a karyotype?

Answer 9

5 million bases. can’t see changes in chromosome smaller than this

Question 10

what abnormalities can be picked up on a karyotype?

Answer 10

abnormal chromosome number, material location, amounts of chromosome material (extra or missing bits).

Question 11

what is aneuploidy?

Answer 11

abnormal number of an individual chromosome e.g. trisomy 21 or monosomy which is 1 chromosome missing

Question 12

what is polyploidy?

Answer 12

abnormal number of sets of chromosomes e.g. monoploid =23, triploid = 69

Question 13

what is triploidy?

Answer 13

3 copies of each chromosome. it’s not compatible with life and usually ends in miscarriage.

Question 14

what causes Down syndrome?

Answer 14

trisomy 21

Question 15

what are typical phenotypes of Down’s syndrome?

Answer 15

intellectual disability, short stature, increased risk of leukaemia and Alzheimer’s, congenital heart disease (AVSD most common), endocrine problems (coeliac + under-active thyroid)

Question 16

what causes Edward syndrome?

Answer 16

trisomy 18

Question 17

what are phenotypic features of Edward’s syndrome?

Answer 17

not compatible with life, very small baby, overlapping fingers, rocker bottom feet (curved like armchair leg), microcephaly, congenital heart/ kidney disease.

Question 18

what causes patau syndrome?

Answer 18

trisomy 13

Question 19

what are phenotypic features of patau syndrome?

Answer 19

one eye, polydactyl, cleft lip/ palate, congenital heart disease, brain abnormalities. most die during pregnancy.

Question 20

what causes klinefelters?

Answer 20

xxy

Question 21

what are phenotypic features of klinefelters?

Answer 21

tall, infertile, little facial or body hair

Question 22

what causes turner syndrome?

Answer 22

xo

Question 23

what are phenotypic features of turner syndrome?

Answer 23

infertility, short, lymphoedema, webbed/broad neck, congenital heart disease, endocrine abnormalities.

Question 24

what is a deletion within chromosomes?

Answer 24

loss of a section of genetic material from a chromosome.

Question 25

what is a duplication within chromosomes?

Answer 25

gain of a section of genetic material from a chromosome.

Question 26

what is a microdeletion?

Answer 26

a loss of a segment of genetic material which is too small to be seen on a karyotype.

Question 27

what is a microduplication?

Answer 27

a gain of a segment of genetic material which is too small to be seen on a karyotype.

Question 28

what causes Di George syndrome?

Answer 28

22q11.2 microdeletion. deletion on the long arm of chromosome 22 at position 11.2

Question 29

what are phenotypic features of Di George syndrome?

Answer 29

congenital heart + kidney disease, problems w/ palate therefore nasal speech, hypocalcaemia, intellectual disability, increased risk of psychiatric disorders.

Question 30

what causes prader willi syndrome?

Answer 30

15q11.2-q13 deletion. deletion on long arm of 15. (if on maternal chromosome then it is angelman's syndrome)

Question 31

what are phenotypic features of Prader Willi syndrome?

Answer 31

low tone at birth, short, hyperphagia (extreme hunger), challenging behaviour, intellectual disability, no/incomplete puberty.

Question 32

what is a chromosome translocation?

Answer 32

relocation of chromosome material to wrong place(s)

Question 33

what is a reciprocal translocation?

Answer 33

2 different chromosomes exchange segments with each other.

Question 34

what is a robertsonian translocation?

Answer 34

an acrocentric chromosome attaches to another at the centromere.

Question 35

what is a balanced translocation?

Answer 35

all chromosome material present but in the wrong place.

Question 36

what is an unbalanced translocation?

Answer 36

loss and/or gain of chromosome material when relocating

Question 37

what causes chronic myeloid leukaemia?

Answer 37

reciprocal translocation between chromosomes 9 and 22 -> results in Philadelphia chromosome. BCR gene from 22 fuses w/ ABL gene from 9 making fusion oncogene BCR::ABL. BCR::ABL causes mutant protein production causing conversion of normal bone marrow stem cells into leukaemic cells.