Chromosomal Abnormalities

Question 1

What is cytogenetics?

Answer 1

Study of the genetic constitution of cells through the visualisation and analysis of chromosomes

Question 2

Why would someone be referred to cytogenetics?

Answer 2

• Prenatal diagnosis
• Birth defects
• Abnormal sexual development
• Infertility
• Recurrent fetal loss (3 or more)

Question 3

What is involved in chromosome analysis?

Answer 3

• Count the number of chromosoms
• Identify each chromosome pair
• Assess if there is any missing/extra material

Question 4

What is aneuploidy?

Answer 4

Loss/gain of whole chromosomes - abnormal number of chromosomes in a cell

Question 5

How does aneuploidy arise?

Answer 5

Errors in meiosis

Question 6

What is Down syndrome?

Answer 6

Trisomy 21

Question 7

What is Patau syndrome?

Answer 7

Trisomy 13

Question 8

What is Edwards syndrome?

Answer 8

Trisomy 18

Question 9

What is Turner syndrome?

Answer 9

45, X

Only one normal X chromosome, rather than two

Question 10

What is polyploidy?

Answer 10

Gain of a whole haploid set of chromosomes
Triploidy 3n
Usually spontaneously aborts

Question 11

What is the main cause of polyploidy?

Answer 11

Fertilisation of an egg by more than one sperm

Question 12

How is aneuploidy caused?

Answer 12

Originates from non-disjunction at one of the meiotic cell divisions, forming gametes with a missing chromsome and an extra chromosome

Question 13

What happens when aneuploidy occurs during mitotic cell division?

Answer 13

Causes mosaicism (two cell populations in an individual)

Question 14

What is anaphase lag?

Answer 14

Chromosomes can be left behind at cell division because of defects in spindle function or attachment of chromosomes leading to the loss of a chromosome

Question 15

What are some characteristics of individuals with Down syndrome?

Answer 15

Characteristic facial features, intellectual disability, heart defects, early alzheimers

Question 16

What are some characteristics of individuals with Edward syndrome?

Answer 16

Small lower jaw, rocker bottom feet, overlapping fingers

Question 17

What are some characteristics of individuals with Patau syndrome?

Answer 17

Multiple congential abnormalities, polydactyly, holoprosencephaly

Question 18

Why is a single X chromosome a problem?

Answer 18

Turner syndrome patients will be monosomic for genes in the PARs. SHOX gene (within PAR) associated with short stature.

Question 19

What are some characteristics of individuals with Turner syndrome?

Answer 19

Short sstature, heart defects, mild learning disabilities, neck webbing, infertility

Question 20

What is mosaicism?

Answer 20

Presence of 2 or more cell lines in an individual, usually caused by mitotic non-disjunction

Question 21

What does the degree of mosaicism depend on?

Answer 21

When mitotic error occured:
First post zygotic division
-no mosaicism looks like a meiotic event
Subsequent divisions
-3 cell lines, monosomy cell line usually lost

Question 22

What are reciprocal translocations?

Answer 22

Reciprocal translocations are usually an exchange of material between nonhomologous chromosomes. No loss of genetic material.

Question 23

What chromosome mutations are there within one chromosome?

Answer 23

Deletion, duplication, inversion, ring chromosome, isochromosome

Question 24

What is an isochromosome?

Answer 24

Creation of two non identical chromosomes, one is a combination of the two short arms and the other is a combination of the two long arms

Question 25

What is a ring chromosome?

Answer 25

Loss of telomeres or ends of both arms and formation of a ring

Question 26

What chromosome mutations are there within two chromosomes?

Answer 26

Inversion, reciprocal translocation and robertsonian translocation

Question 27

What are robertsonian translocations?

Answer 27

Rearrangement of genetic material between two chromosomes; the q arm of two acrocentric chromosomes combine to form one ‘super chromosome’ with the loss of both p arms

Question 28

What is the largest and smallest chromosome?

Answer 28

Largest = 1
Smallest = 22

Question 29

On which chromosomes can robertsonian translocations occur?

Answer 29

13, 14, 15, 21, 22

Question 30

What is microarray comparative genomic hybridisation?

Answer 30

Examine the whole genome at high resolution