Chromosome Abnormalities/Mutations/Analysis

Question 1

Give the three main types of chromosome abnormalities

Answer 1

Numerical
Structural
Mutational

Question 2

Give types of numerical chromosome abnormalities

Answer 2

Non-disjunction
Autosomal aneuploidy
Sex linked aneuploidy

Question 3

Describe the mechanism of non-disjunction

Answer 3

Problem in meiosis to give a disomy (two copies of a chromosome in a daughter cell/gamete)

Question 4

What does non-disjunction give rise to in offspring?

Answer 4

Trisomy (an extra chromosome in a cell)

Question 5

What is caused by trisomy in chromosome 21?

Answer 5

Down syndrome

Question 6

Trisomy in chromosome 13?

Answer 6

Patau syndrome

Question 7

Chromosome 18?

Answer 7

Edwards syndrome

Question 8

Chromosome 45,X?

Answer 8

Turner syndrome

Question 9

Chromosome 47,XXY?

Answer 9

Klinefelter syndrome

Question 10

Give some features of Patau syndrome

Answer 10

• dysmorphic features

- mental retardation

Question 11

Features of Edwards syndrome?

Answer 11

• developmental problems

Question 12

Features of Turner syndrome?

Answer 12

• female
• short stature
• neck webbing
• widely spaced nipples

Question 13

Features of Klinefelter syndrome?

Answer 13

• male
• infertile
• small testes
• tall
• long limbs

Question 14

Give types of structural chromosome abnormalities

Answer 14

Balanced/unbalanced reciprocal translocation

Robertsonian translocation

Inversion

Deletion

Insertion

Question 15

What is reciprocal translocation?

Answer 15

Chromosome breaks in two and forms two new derivatives

Balanced - same amount of each at the end; phenotypically normal

Unbalanced - from normal parent and another with balanced translocation; gives rise to trisomy/monosomy in offspring

Question 16

What is Robertsonian translocation?

Answer 16

Occurs in acrocentric chromosomes;

• long arms (q) attach to long arms
• short arms (p) attach to short arms

Gives rise to abnormalities in offspring if they receive unequal amounts of a chromosome

Question 17

Give two types of inversion

Answer 17

Paracentric inversion - abnormal fixing, no centromere involvement

Pericentric inversion - abnormal fixing in the centromere region

Question 18

Give the four types of mutational coding abnormalities

Answer 18

Silent
Missense
Nonsense
Frame shift

Question 19

What is the difference between transitions and transversions?

Answer 19

Transitions - purine mutates to purine, pyrimidine mutates to pyrimidine

Transversions - purine mutates to pyrimidine, pyrimidine mutates to purine

Question 20

Give types of mutational chromosome abnormalities

Answer 20

Germline/somatic
Gene disruption
Polymorphism

*All may be coding/non-coding/point mutations

Question 21

Give the main types of abnormality detection

Answer 21

PCR
ARMS
RFLP
DNA sequencing

Question 22

What is PCR?

Answer 22

Polymerase chain reaction

Question 23

What happens during PCR?

Answer 23

• denaturation to create a single-stranded DNA
• annealing (bonding of primers to DNA template
• extension of primers using DNA polymerase to synthesise new DNA strands behind them
• repetition to amplify target DNA
• analysis using gel electrophoresis

Question 24

What is ARMS?

Answer 24

Amplification refractory mutation system

Question 25

What happens during ARMS?

Answer 25

• sequence specific primers will only amplify if the target allele is present
• wild type allele amplified by a normal primer
• mutant allele amplified by a mutant amplification
• then undergoes PCR and gel electrophoresis

Question 26

What is RFLP?

Answer 26

Restriction fragment length polymorphism

Question 27

What happens during RFLP?

Answer 27

• restriction enzyme cuts DNA strand at different lengths

- gel electrophoresis

Question 28

What is DNA sequencing?

Answer 28

the process of determining the precise order of nucleotides within a DNA molecule

Question 29

How does DNA sequencing work?

Answer 29

• double helix denatured
• one strand isolated
• radioactively labelled primer used to replicate strand
• primer elongates to match strand and reform a double strand (stops at ddNTP)
• gel electrophoresis (coloured dye shows up)