Week 10 - Chromosomal Abnormalities

Question 1

What is the long arm of a sub-metacentric chromosone called?

Answer 1

q arm

short = p arm

Question 2

What is a metacentric chromosone?

Answer 2

centromere is in the centre

p and q arms are of equal length

eg human chromosones 1 and 3

Question 3

What is an acrocentric chromosone?

Answer 3

short p arm can be deleted without harm

eg chromosone 14, 21, Y

Question 4

What are autosomes?

Answer 4

chromosones 1-22

Question 5

Where is this gene located?

11p15.5

Answer 5

chromosone 11

short arm

main band 1

sub-band 5

sub-sub band 5

(bands are numbered according to increasing distance from centromere)

Question 6

What is a karyotype?

Answer 6

a description of a chromosone set

eg 46, XX = normal female

Question 7

What syndrome does this individual have?

47, XX, +21

Answer 7

female with Down Syndrome

Question 8

What is the karyotype for an individual with Turner Syndrome?

Answer 8

45, X

Question 9

What is cri du chat syndrome?

Answer 9

an individual with the karyotype

46, XY (or XX), del(5p)

deletion of the short arm of chromosone 5

name comes from the characteristic cry of affected infants

Question 10

What are the two main types of aneuploidy?

aneuploidy - abnormal number of chromosones

Answer 10

trisomy - presence of an extra chromosone

monosomy - absence of a chromosone

(polyploidy - presence of extra set(s) of chromosones)

Normal = 46

consequence is too little/too much protein produced as a result of the extra genes

Question 11

How do aneuploidies arise?

Answer 11

non-disjunction

failure of sister chromatids to separate properly during cell division

can occur at meiosis I or meiosis II

Question 12

What is a disomic gamete?

Answer 12

a gamate with two copies of a chromosone rather than one

if fertilised this gamate will give a trisomy individual

nullisomic gamate - no copies of a specific chromosone

Question 13

What is Patau syndrome?

Answer 13

Trisomy 13

47, XY, +13

Question 14

What are the consequences of males gaining an extra X chromosone?

karyotype - XXY

Answer 14

tall, infertile, possible poorly developed secondary sexual characteristics and slight reduction in IQ

Klinefelter syndrome

Question 15

What is the number of inactive X chromosones in an individual with the karyotype XXX?

Answer 15

2

in female somatic cells only one randomly chosen X chromosone is active

regardless of number present only one X chromosone is active

Question 16

What is an invasive method of diagnosing common aneuploidies prenatally?

Answer 16

amniocentesis and chromosonal analysis

usually definitive, 1% risk of miscarriage

Question 17

Does an inversion of a chromosnone affect the health of the individual?

Answer 17

no medical problems

risk of loss/gain of material during recombinationbetween normal chromosone and chromosone with inversion

Question 18

What is reciprocal translocation?

Answer 18

exchange of material between non-homologous chromosones

no net loss or gain of material

Question 19

What kind of karyotypes do cancer cells have?

Answer 19

very abnormal

structural and numerical changes, aneuploidy is a ubiquitous feature

Question 20

Why do sex chromosone abnormalities cause mild symtoms?

Answer 20

X chromosone inactivation

Question 21

What is the ‘Philadelphia chromosone’?

Answer 21

a reciprocal translocation between chromosone 9 and 22

gives rise to fusion gene bcr-acl

asssociated with chronic myelogenous leukaemia

t(9;22)(q34;q11)

Question 22

What is the effect of the BCR-ABL fusion gene created by the ‘Philadelphia translocation’?

Answer 22

ABL kinase is always switched on resulting in unregulated cell division leading to cancer

Question 23

What is trisomy 18 also known as?

Answer 23

Edwards Syndrome

very severe condition, most babies born with trisomy 18 in every cell in their body will die before infancy