Cromosmal Mutationsh

Question 1

Define chromosomal mutations.

Answer 1

Refers to alterations in the structure or number of chromosomes, which can have profound effects on an organism’s phenotype.

Question 2

What are the levels of packing to form a chromosome?

Answer 2

DNA
Nucleosome
Chromatin
Chromatin loops
Condensed heterochromatin
Compacted chromosome

Question 3

What are the two arms found in human chromosomes?

Answer 3

P (short) arm
Q (long) arm

Separated from each other only by the centromere

Question 4

Define centromere and its function.

Answer 4

Specialised DNA sequence of a chromosome that links a pair of sister chromatids.

During mitosis, spindle fibres attach to the centromeres via the kinetochore.

Question 5

Define alpha satellite.

Answer 5

Repeats of a 171-base DNA sequence

Question 6

Function of centromere associates proteins.

Answer 6

During cell division centromere associated protein form kinetochore that forms the point of contact for the spindle fibres

Question 7

Define telomeres.

Answer 7

Specialised repeated DNA sequences (TTAGGG) that protect ends of chromosomes

Question 8

Define subtelomeres.

Answer 8

The chromosome parts between protein reach areas and the telomeres

Question 9

Role of telomerase.

Answer 9

During chromosome replication of lagging DNA strand, end is left unreplicated

Telomerase extends these unreplicated ends

Question 10

List the chromosome e classification based on centromere position.

Answer 10

Metacentric
Submetacentric
Acrocentric
Telocentric

Question 11

Which chromosomes are metacentric?

Answer 11

1,3,16,19,20

Question 12

Which chromosomes are acrocentric?

Answer 12

13,14,15,21,22 and Y

Question 13

How many chromosomes are telocentric?

Answer 13

None

Question 14

Define karyotype.

Answer 14

An individuals collection of chromosomes

Human karyotype has 46 chromosomes

Question 15

Method of karyotyping:

Answer 15

5ml venous blood (use WBCs)
Add phytohemagglutinin and culture medium
Culture at 37 degrees for 3 days
Add colchicine and hypotonic saline
Cells fixed
Spread cells into kalide by dropping
Digest with trypsin and stain with Giemsa
Analyse “metaphase spread”

Question 16

Describe G banding technique.

Answer 16

Provides information on the structure of the individual chromosomes.

Technique uses Giemsa dye to stain chromosomes after pre-treatment with a protein degrading enzyme-trypsin

Question 17

Describe FISH

Answer 17

Fluorescence in situ hybridisation is a molecular cytogenetic technique used to identify specific chromosomal aberrations or for chromosomal gene mapping.

Question 18

FISH process

Answer 18

FISH is performed on fixed chromosomes on a microscopic slide.

Once DNA is denatured, two fluorescently labelled DNA probes are used in combination to analyse each complementary location in question

Question 19

Roles of the two probes in FISH

Answer 19

First probe serves as a control and hybridises with the DNA on target chromosome but outside of the targeted region

Second probe hybridises to a target location in the individuals DNA sequence

Question 20

Describe constitutive chromosome abnormalities.

Answer 20

All tissues hold the same anomaly

Question 21

Describe acquired chromosomal abnormalities.

Answer 21

Only one organ is involved, the other tissues are normal.

Question 22

Describe homogenous chromosomal abnormalities.

Answer 22

When all the cells carry the anomaly

Question 23

Describe mosaic chromosome abnormalities

Answer 23

When only some cells carry the anomaly

Question 24

Describe numerical chromosomal abnormalities

Answer 24

When in humans a total number of chromosomes is NOT 46

Question 25

Describe structural chromosomal abnormalities

Answer 25

Defects that include missing, extra, trans located or inverted genetic material within a chromosome.

Question 26

Describe euploidy.

Answer 26

Nirmak number and sets of chromosomes

Question 27

Describe polyploidy.

Answer 27

Presence of three or more complete sets of chromosomes

Question 28

Describe aneuploidy.

Answer 28

Presence of additional or missing individual chromosomes

Question 29

Describe balanced chromosomal rearrangements.

Answer 29

Type of chromosomal structural variant involving chromosomal rearrangements without cytogenetically apparent gain or loss of chromatin e.g. translocations, inversion, insertions

Question 30

Describe unbalanced rearrangements.

Answer 30

Include deletions, duplications, or insertions if a chrimsime segment when there is additional if missing genetic info

Question 31

Types of aneuploidy

Answer 31

Monosomy-one less chromosome Trisomy-one additional chromosome Nullisomy-where a pair of homologous chromosomes is missing

Question 32

Define autosomal aneuploidy

Answer 32

All such abnormalities that do not involve the sex chromsomes

Question 33

Define sex chromosome aneuploidies

Answer 33

All such abnormalities that involve the sex chromosomes

Question 34

Characteristics of Turner syndrome

Answer 34

Monosomy X, Karyotype 45, X0 Normal intelligence Dysmorphic-webbed neck, broad chest with widely spaced nipples Primary amenorrhoea and lack of secondary sexual characteristics Coarctation of the aorta

Question 36

Describe Klinefelter syndrome.

Answer 36

Karyotype 47, XXY Nirmak intelligence Usually taller than average Disproportionally long limbs 30-50%. gynaecomastia Infertility

Question 37

Describe submicroscopic deletions.

Answer 37

Chrimsime deletions that are too a,ll to be deleted by light microscopy using conventional cytogenetic methods (typically ien to three Mb long)

Question 38

Describe reciprocal translocation

Answer 38

Segments from two different (non-homologous) chrimsime bream and swap positions

Question 39

Describe robertsonian translocation

Answer 39

Where two acrocentric chromosomes fuse their centromeres, losing their short arms and forming one large chromosome

Question 40

Describe paracentric inversion

Answer 40

Two breaks occur in the same arm of a chromosome

Question 41

Describe pericentric inversions

Answer 41

An inversion that includes the centromere

Question 42

Describe insertion mutation.

Answer 42

The insertion of a larger sequence into a chromosome.

Question 43

Describe a ring chromosome.

Answer 43

Abnormal circular structures formed when a chrimsime breaks at both ends and fuses, often causing significant genetic material loss

Question 44

Describe isochromosomes and the most frequent one

Answer 44

Abnormal chromosomes with identical arms Isochromosome Xq- found in 15-18% of turner syndrome cases

Question 45

Describe uniparental disomy (chromosome 15) with examples.

Answer 45

Rare genetic phenomenon where an individual inherits both copies of a chromosome pair from one parent instead of one from each E.g. angel an syndrome and prader-Willi syndrome

Question 46

How is ribosomal DNA (rDNA) arranged in human cells?

Answer 46

Arranged in ten clusters of multiple tandem repeats

Question 47

What are the two parts of the rDNA repeats?

Answer 47

13kb long ribosomal part, containing three genes coding for 18S, 5.8S and 28S RNAs of the ribosomal particles 30kb long intergenjc spacer (IGS)

Question 48

What are rDNA clusters known as and where are they found?

Answer 48

Nucleolus Organising Regions (NORS) Situated on the shirt arms of the acrocentric chromosomes

Question 49

Describe transposable element (TE, transposon, or jumping gene)

Answer 49

DNA sequence that can change its position within a genome, sometimes creating or reversing mutations and altering the cells genetic identity and genome size.

Question 50

Role of transposons.

Answer 50

Drive evolution of genomes by facilitating the translocation of genomic sequences, the shuffling of exons, and repair of double stranded breaks

Question 51

Describe synteny

Answer 51

Conservation of the relative order of genes or genetic markers across different species genomes.