MGD S10 - Chromosome Abnormalities Flashcards Preview

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Flashcards in MGD S10 - Chromosome Abnormalities Deck (29):
1

What are chromosomes made up off?

Chromosomes are made up of chromatin Chromatin is made up of:

- DNA

- Non-histone proteins

- RNA

- Histones (H1, H2A, H2B, H3, H4)

2

What components make up chromatin?

Histones, RNA, DNA and non-histone protein

3

List the types of histone and their characteristics

H1, H2A, H2B, H3, H4 H1 - Varies between species

H2A, H2B, H3 and H4 directly interact with the DNA H3 and H4 are highly conserved and are responsible for bead on a string structure

4

What is euchromatin?

Lightly packed chromatin, often under active transcription

5

What is heterochromatin?

Tightly packed chromatin and not under active transcription

6

What are numerical chromosomal abnormalities?

Number of chromosomes other than 46

7

What are the two types of numerical chromosomal abnormalities?

Polyploidy - cells containing more than two paired (homologous) sets of all chromosomes. Caused by polyspermy

Aneuploidy - (an abnormal number that is not a multiple of the haploid number) Monosomy is a loss of one chromosome i.e one chromosome pair missing Trisomy is a gain of one chromosome i.e one “chromosome pair” exists as a triplet

8

What are structural chromosomal abnormalities?

Physical changes to one or more chromosome

9

What are two types of structure abnormalities?

Balanced - Change does not result in missing or extra genetic information

Unbalanced - Change results in missing or extra genetic information

10

List all the mutations that can occur within one chromosome

1) Deletion

2) Duplication

3) Inversion

4) Ring chromosome

5) Isochromosome; balanced - the arms are mirror images

11

How does a ring chromosome form?

Loss of the telomeres at ends of both arms forming a ring

12

List the mutations that occur between two chromosomes?

1) Inversion

2) Reciprocal Translocation

3) Robertsonian Translocation

13

What is an inversion mutation?

No loss of genetic material, but as rearrangement of genetic material to a non-homologous chromosome

14

What is reciprocal translocation (chromosome abnormality)?

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

15

What is a robertsonian translocation?

Rearrangement of genetic material between two chromosomes; the q- arms (long arms) of two afrocentric chromosomes combine to form one 'super-chromosome' with the loss of both p-arms

16

What is the difference between reciprocal and robertsonian translocation

Reciprocal is the exchange of genetic material between two non-homologous chromosomes whereas Robertsonian involves the exchange of genetic material produced two q arms from two acrocentric chromosomes to form a super chromosome and loss of the two small p arms

17

What is a karyotype?

Picture of the systematic assortment of the complete set of chromosomes of an individual, starting with chromosome 1 and ending with the sex chromosomes

18

How is a karyotype produced?

Produced by ‘cut and paste’ of chromosome pictures by hand or computer to make organised set of metaphase chromosomes

19

Describe chromosome nomenclature

Number of chromosomes-comma-X chromosomes-Y chromosomes + or – for loss or gain of genetic material State whether in p or q arm

E.g. Normal Female = 46,XX and a Normal Male is 46,XY

E.g. 5p- means ‘missing a segment of the p-arm on chromosome 5

20

Why would a patient be referred for karyotyping?

Congenital: - Prenatal screening e.g. family history

- Recurrent foetal loss

- Infertility

- Birth defects e.g. mental retardation

- Abnormal sexual development e.g. Klienfelter’s Syndrome

- Acquired Abnormalities - Leukaemia and related diseases

21

What can be identified from FISH?

Rearranged chromosomes, marker chromosomes and microduplications and microdeletions

22

What is microarray used for?

High resolution of 5-10 megabases means that microarray can be used to test for submicroscopic chromosome abnormalities Used for individuals with suspected unbalanced chromosomal abnormalities

23

What is uniparental disomy? (UPD)

Uniparental disomy (UPD) occurs when a person receives two copies of a chromosome, or of part of a chromosome, from one parent and no copy from the other paren

24

Why is imprinting significant to UPD?

Imprinted chromosomes show differential expression of specific genes depending on the parental origin of the chromosome If chromosome involved is not imprinted then UDP has no phenotypic effect

25

Name a UPD syndrome

Prader-Willi (15)

26

What is the most common mechanism to generate UDP?

Trisomy rescue

27

Describe non-invasive pre-natal testing (NIPT)

Cell free DNA is present in plasma fraction of maternal blood

28

What can NIPT be used to test for?

Chromosome aneuploidy, foetal sex, single gene disorders

29

What is the advantage of NIPT compared to invasive pre-natal testing

Removes miscarriage risk