Genomics and chromosomal diseases

Question 1

What is genomics?

Answer 1

The study of the whole genome of organisms. (It incorporates elements form genetics.) Includes both heritable mutations/diseases and mutations/diseases occuring “de novo”.

Question 2

What is chromatin?

Answer 2

DNA and packaging proteins.

Question 3

What is meant by exome?

Answer 3

The exome includes all the exons in the genome (= all the genes.)

Question 4

What is copy number?

Answer 4

The number of copies of a particular gene in the genome of an individual.

Question 5

Name some laboratory tests used in chromosomal analysis.

Answer 5

Traditional (G-band) chromosomal analysis.
FISH.
Quantitative Fluorescence - Polymerase Chain Reaction (QF-PCR).
Chromosomal microarray.
Copy number variations in exome sequencing.

Question 6

True or false: Mitosis gives rise to two diploid cells.

Answer 6

True. (The daughter cells are identical diploids.)

Question 7

True or false: Meiosis gives rise to four genetically identical daughter cells.

Answer 7

False. Meiosis gives rise to four genetically distinct daughter cells.

Question 8

At which times are the chromosomes in cells visible?

Answer 8

The chromosomes are only visible during cell division.

Question 9

At which stage of cell division are the cells arrested when doing a standard G-band chromosome analysis.

Answer 9

Metaphase: The stage in which the chromosomes are in their second-most coiled and condensed form.

Question 10

What is a karyogram?

Answer 10

A graphical presentation of a person’s chromosomes.

Question 11

What is meant by karyotype?

Answer 11

A person’s individual collection of chromosomes, commonly used to described/identify abnormal structures or numbers of chromosomes.

Question 12

What is the normal karyotype for a female? What is the normal karyotype for a male?

Answer 12

46, XX is the normal karyotype for a female.

46, XY is the normal karyotype for a male.

Question 13

What laboratory test for chromosomal analysis is referred to as a rapid test/”hurtigtest” for aneuplodies?

Answer 13

Qualitative Fluorescence - Polymerase Chain Reaction (QF-PCR).

Question 14

What is meant by aneuploidy?

Answer 14

The over- or under-representation of one (or a few) chromosome(s) or one (or a few) chromosomal segment(s).

Question 15

For which laboratory test for chromosomal analysis is the following statement true: “The test only detects unbalanced abnormalities”?

Answer 15

Chromosomal microarrays.

Question 16

What are some indications for conducting a standard G-band chromosome analysis?

Answer 16

Three or more spontaneous abortions.
Suspected structural chromosomal aberration.
Suspected sex chromosome abnormality (growth, pubertal development).

Question 17

What are some indications for conducting a QF-PCR?

Answer 17

Prenatal diagnostics.

Learning difficulties.

Question 18

What are some indications for conducting a SNP-array?

Answer 18

Intellectual disability, severe autism.

Major or several minor congenital malformations.

Question 19

What is the normal number of chromosomes in gametes?

Answer 19

Gametes are haploids and normally have 23 chromosomes.

Question 20

What is non-disjunction?

Answer 20

The failure of homologous chromosomes or sister chromatids to separate properly during cell division.

There are three forms of non-disjunction:

1) Failure of separation of homologous chromosomes during meiosis 1
2) Failure of separation of sister chromatids during meiosis 2
3) Failure of separation of sister chromatids during mitosis.

Question 21

What is Klinefelter syndrome?

Answer 21

Over-representation of the X-chromosome in males. Karyotype 47, XXY (or 48 XXXY and so on …).

Question 22

What are some clinical features associated with XYY syndrome?

Answer 22

Tall stature.
Acne.
Learning difficulties (are more common than in the general population. Delays in speech and language development may occur.)

Question 23

What is the karyotype for Turner syndrome? What are some clinical features associated with Turner syndrome?

Answer 23

45, X.
Short stature, webbed neck, shield chest, underdeveloped breasts, widely spaced nipples, rudimentary ovaries, infertility.

Question 24

What are the three most commmon trisomies?

Answer 24

Trisomy 21 (Down’s syndrome), trisomy 13 (Patau syndrome) and trisomy 18 (Edwards syndrome).

Question 25

What is a reciprocal translocation?

Answer 25

A chromosome abnormality caused by an exchange of parts between non-homologous chromosomes. Two detached fragments from non-homologous chromosomes are switched.

Question 26

What is a Robertsonian translocation?

Answer 26

A translocation occuring in two of five acrocentric chromosome pairs, namely chromosome pair 13, 14, 15, 21 and 22. The participating chromosomes break at their centromeres and the q-arms fuse to form a single, large chromosome with a single centromere. (The p-arms are lost.)

It is the most common form of structural chromosome abnormality in humans and may cause genetic disorders as trisomy 21 (Down’s syndrome) or trisomy 13 (Patau syndrome).

Question 27

What is the difference between a balanced and an unbalanced chromosomal translocation?

Answer 27

In a balanced translocation there is an even exchange of material with no genetic information extra or missing, and ideally full functionality.

In an unbalanced translocation the exchange of chromosome material is unequal resulting in extra or missing genes.

Question 28

What is an acrocentric chromosome?

Answer 28

A chromosome in which the centromere in located near the end of the chromosome.

Question 29

What are the two main types of chromosomal translocations?

Answer 29

Reciprocal translocation and Robertsonian translocation.

Question 30

Name some examples of microdeletion syndromes.

Answer 30

Smith Magenis syndrome.
Williams syndrome.
DiGeorge syndrome.

Question 31

What are the types of chromosomal inversions?

Answer 31

Paracentric inversion and pericentric inversion.

Question 32

What is a paracentric inversion?

Answer 32

A paracentric inversion does not include the centromere of the chromosme. Both breaks occur in one arm of the chromosome.

Question 33

What is a pericentric inversion?

Answer 33

A pericentric inverson includes the centromere. There is a break point in each arm of the chromosome.