Chromosome Abnormalaties

Question 0

Describe polyploidy and its cause

Answer 0

Gain of a whole haploid set of chromosomes

Due to polyspermy

Question 1

Explain how genetic information in a cell is organaised into chromosomes

Answer 1

DNA is wrapped around an octamer of histones 2xH2A,H2B,H3,H4
166 bp per octamer and histone H1 stabilises
Higher order structure is a solenoid, which is stabilised by hanging loops of DNA onto a protein scaffold - chromatin

Question 2

Describe aneuploidy and its cause

Answer 2

Any variation in chromosome number

Due to non-disjunction at one of the meiotic cell divisions, failure of sister chromosomes to properly seperate

Question 3

What is meant by a balanced mutation?

Answer 3

Exchange or rearrangement of genetic material that doesnt cause any missing or extra genetic information

Question 4

What is meant by an unbalanced mutation?

Answer 4

Structural chromosomal changes cause missing or extra genetic information

Question 5

Describe ‘inversion’ chromosome abnormality

Answer 5

No loss, but re-arrangement of genetic information

Question 6

Describe ‘ring chromosome’ abnormality

Answer 6

Loss of telomeres or end of both arms, forming ring

Question 7

Describe ‘isochromosome’ abnormality

Answer 7

Creation of 2 non-identical chromosomes, one a combination of two short arms, one too long

Question 8

Describe ‘translocation’ chromosome abnormality

Answer 8

No loss of genetic material, but rearrangement if genetic material to a non-homologus chromosome

Question 9

Describe reciprocal transllcation chromosome abnormality

Answer 9

No loss of genetic material, but an exchange of genetic material between two non-homologus chromosomes

Question 10

Describe a robertsonian translocation

Answer 10

Re-arrangement of genetic material between two chromosomes; the q arms of two acrocentric chromosomes combine to form one super chromosome with the loss of both p arms

Question 11

What is karyotyping and why is it used?

Answer 11

It is a test to determine the number of chromosomes in a sample of cells
Produced by cut and paste of chromosome pictures knto a systematically organaised set of metaphase paired chromosomes
Chromosomes are numbered and grouped according to size and position of centromere
Allows us to check for structural changes in disease

Question 12

Outline reasons for referral of patients for karyotyping

Answer 12

Congenital abnormalaties:

• prenatal screening - downs, family history of chromosomal abnormalaty, abnormal ultrasound
• birth defects - malformations, mental retardation
• abnormal sexual development - klienfellers syndrome
• inferitlity
• recurrent fetal loss

Aquired: leukaemia

Question 13

What is the importance of FISH when detecting chromosomal abnormalities

Answer 13

Through nucleic acid hybridaisation the degree kd sequence identity can be determined and specefic sequences (genes) can be detected and located on a given chromosome