Chromosome Abnormalities

Question 1

Chromosomes are made up of

Answer 1

Chromatin

Question 2

Euchromatin is…

Answer 2

Lightly packed chromatin

Often under transcription

Question 3

Heterochromatin is….

Answer 3

Densely packed chromatin

Question 4

2 types of numerical chromosomes abnormalities

Answer 4

Polyploidy

Aneuploidy

Question 5

What is polyploidy

Answer 5

Containing more than 2 (paired) homologous sets of chromosomes
Eg triploidy, tetraploidy
Often caused by fertilisation by more than 1 sperm

Question 6

What is aneuploidy

Answer 6

Abnormal number of chromosomes - not a multiple of the haploid number
Either :
* monosomy - loss of 1 chromosome
*trisomy - gain of 1 chromosome

Question 7

What causes aneuploidy ?

Answer 7

Originates from non-disjunction at meiotic division, where there is failure of chromosomes to separate properly at meiosis 1or2, specifically in anaphase

Question 8

What is anaphase lag?

Answer 8

Chromosomes are left behind at cell division because of defects in spindle function or chromosome attachment

Question 9

What does non disjunction in mitosis cause?

Answer 9

2 populations of cells with different karyotypes, so person is mosaic

Question 10

Structural chromosome abnormalities can either be ….

Answer 10

Balanced - no extra / missing genetic material

Unbalanced - extra/missing genetic material

Question 11

Mutations within one chromosome are….

Answer 11

Deletion
Duplication
Inversion (rearrangement)
Ring chromosome (loss of tetromeres or both arms and formation of a ring)
Isochromosome (creation of 2 non identical chromosomes, 1 = combination or 2 short arms other = combination of 2 long arms)

Question 12

Mutations within 2 chromosomes

Answer 12

Inversion = no loss of genetic material- rearrangement of genetic material to a non-homologous chromosome
Reciprocal translocation - no loss of genetic info, exchange of genetic material between 2 non homologous chromosomes
Robertsonian translocation = rearrangement of genetic material between 2 chromosomes the q arms of 2 acrocentric chromosomes combine to form one super chromosome - loss of both p arms. Occurs mostly between 13:14/14:21/14:15

Question 13

FISH is good as….

Answer 13

Is a technique in which a single stranded nucleic acids are permitted to interact so that complexes or hybrids with sufficiently similar complementary sequences.
Degree of sequence identity can be determined, specific sequences detected and located on a given chromosome

Question 14

Reasons for referring patients for karyotyping

Answer 14

Prenatal screening (downs syndrome/ family history of chromosome abnormalities) 
Birth defects 
Abnormal sexual development
Infertility 
Recurrent foetal loss
Leukaemia and related disorders