3 - Chromosomal abnormalities

Question 1

cytogenetics

Answer 1

The study of the structure and function of chromosomes

Question 2

what is cytogenetics used for?

Answer 2

Used for the screening and diagnosis of inherited chromosomal disorders

Question 3

Karyotype

Answer 3

a preparation of chromosomes arranged in size order

Question 4

how to make a karyotype

Answer 4

blood sample treated with chemical that stimulates mitosis

another chemical added to stop mitosis at metaphase (double chromosomes but not separated yet)

Question 5

what are the 3 ways to identify a chromosome?

Answer 5

1. length
2. banding pattern
3. centromere placement

Question 6

metacentric

Answer 6

centromere in centre

Question 7

sub-metacentric

Answer 7

centromere is off-centre

Question 8

acrocentric

Answer 8

centromere very close to end

Question 9

What is karyotyping used for?

Answer 9

to detect changes in chromosome number and shape

Question 10

polyploidy

Answer 10

Extra whole sets of chromosomes

Question 11

aneuploidy

Answer 11

Some additional or missing chromosomes

Question 12

monosomy

Answer 12

1 chromosome missing

Question 13

trisomy

Answer 13

1 extra chromosome

Question 14

what is aneuploidy caused by?

Answer 14

non-disjunction of homologous chromosomes

Question 15

what is the only autosomal aneuploidy that permits survival into adulthood?

Answer 15

Down’s Syndrome

Question 16

what is trisomy 21 commonly known as?

Answer 16

Down’s syndrome: 47,XX,+21

Question 17

characteristics of down’s syndrome

Answer 17

• short
• sterile
• mental retardation
• heart defects

Question 18

screening for chromosomal abnormalities

Answer 18

1. amniocentesis and karyotyping
2. blood tests
3. ultrasounds

Question 19

what is the only viable human monosomy?

Answer 19

Turner syndrome: 45,XO

Question 20

characteristics of turner’s syndrome

Answer 20

• phenotypically female
• sterile, as sex organs immature
• treatment via oestrogen replacement

Question 21

Klinefelter syndrome

Answer 21

47, XXY

Question 22

characteristics of Klinefelter’s syndrome

Answer 22

• male with female characteristics
• tall
• sterile

– treated with testosterone replacement

Question 23

What is a deletion mutation?

Answer 23

one nucleotide is taken away from a gene or DNA sequence

Question 24

What is a duplication mutation?

Answer 24

When one or more bases are repeated

Question 25

what is an inversion mutation?

Answer 25

when part of a chromosome breaks off and reattaches backwards

Question 26

what is reciprocal translocation?

Answer 26

The breakage and rejoining of 2 non-homologous chromosomes, with a reciprocal exchange of the broken segments.

Question 27

What is cri du chat syndrome?

Answer 27

absence of short arm of 5th chromosome

Question 28

characteristics of cri du chat syndrome

Answer 28

- cat-like cry - defects in larynx - retardation

Question 29

Prader-Willi Syndrome

Answer 29

Deletion in long arm of chr 15 (15q1.12) | - only occurs when the affected chromosome is inherited from the father, due to genomic imprinting

Question 30

prader willi characteristics

Answer 30

- poor suckling reflex - uncontrollable eating - poor male sexual development

Question 31

Angelman Syndrome

Answer 31

deletion of maternal chromosome 15

Question 32

characteristics of angelman's syndrome

Answer 32

- happy demeanor - innapropriate outbursts of laughter - mental retardation

Question 33

which conditions are caused by translocations

Answer 33

familial down's syndrome and chronic myelotic leukaemia

Question 34

Familial Down’s Syndrome

Answer 34

- accounts for ~5% of Down’s cases | - Translocation carrier t(14;21): one of the chr 21’s is attached to one of the chr 14s

Question 35

Chronic myelocytic leukaemia (CML)

Answer 35

- spontaneous, not heritable - Occurs in 1 per 50-100,000 of the population, most common in middle-aged/elderly - Accounts for 15-20% of all cases of leukaemia

Question 36

what causes Chronic myelocytic leukaemia

Answer 36

22-9 translocation creating BCR-ABL fusion gene

Question 37

BCR-ABL fusion gene

Answer 37

an oncogene that stimulates over-production of white blood cells