fbs 4 9-chromosome aberration

8/12/2019 Fbs 4 9-Chromosome Aberration

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Fig.20.20


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Chromosomes are the factors which distinguish

one species from another.

Enable transmission of genetic information from

one generation to the next.

The study of chromosomes and cell division is

referred to as cytogenetics

Chromosome consist of two identical strandsknown as chromatids or sister chromatids.

The sister chromatids joined at a constriction

known as centromere


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DNA

chromatin

chromatin fibers

fibers connected to

chromosome scaffold

Condenced scaffold

Chromosome


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Centromere consist of repetitive DNA, are

responsible for movement of chromosomes.

Centromere divides chromosomes into short arms

(p=petite) and into long arms (q= grande).

The tip of each chromosome arms is telomere.

According to the position of the centromere,

chromosomes are clasified a metacentric,

submetacentric and acrocentric.


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Metacentric : the centromere is located centraly.

Submetacentric : the centromere is located

between the central and the terminal.Acrocentric : telomere is located in the terminal.

Sometimes acrosentric have apendages called

satellite.

Satellite consists of very large series of simple

short tandemly repeated DNA sequences which are

transcriptionally inactive.

Satellite are clustered around the centromere of

certain chromosomes.


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Chromosome disorder

Numerical

change in number ofchromosome

Structure

change in structure ofchromosome


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Changes in the numbers of chromosomes

Polyploidy

Extra complete sets of chromosomes

3N, 4N, 5N, etc.

Suffix: -ploid or -ploidy

3N = triploid

4N = tetraploid


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Aneuploidy

Extra or missing single chromosomes

2N + 1

2N -1

Suffix: -somy or -somic

2N + 1 = trisomy

2N - 1 = monosomy2N + 2 = tetrasomy


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Down Syndrometrisomy 21

Pataus syndrometrisomy13 Edwards syndrometrisomy18

Trisomy 16 in first trimester spontaneous

miscarriages

1.Trisomy

Numerical abnormality


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Derives its name from Dr.Langdon Down who first

described.

The incidence is approximately 1 in 650

There are extra chromosome of number 21

Non disjunction

Translocation between 14 and 21

The most explanation is maternal age.


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Clinical feature

Hypotonia low muscle tone

The facial characteristics of upward sloping

Small ears

Protruding tongue

Single palmer crease

Congenital cardiac abnormalities.


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The incidence approximately 1 :5000

This syndrome affected infant dying in the first few

week of life.

Cardiac abnormalities

Mental retardation.

Trisomy 13 :

Non disjunction

Mosaicism

Robertsonian translocation.


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Mosaicism

Somatic origin mitotic non

disjunction

Meiotic origin meiotic nondisjunction

Chromosome 46/47

mosaic type


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Somatic originMeiotic origin


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Robertsonian translocation

Chromosomal rearrangement that in humans

occurs in the five acrocentric chromosome pairs,

namely 13, 14, 15, 21, and 22

Robertsonian translocations are between

chromosomes 13 and 14, 14 and 21, and 14

and 15 the long arms of two acrocentric

chromosomes fuse at the centromere and

the two short arms are lost

Balanced translocation no extra material

form chromosome 13 affected in

offspring


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Nervous system

Mental and motor challenged

Microcephaly

Holoprosencephaly(failure of the forebrain todivide properly).

Structural eye defects,

Musculoskeletal and cutaneous

Polydactyly (extra digits) Low-set ears

Prominent heel

Deformed feet


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Abnormal palm pattern

Overlapping of fingers over thumb

Cutis aplasia (missing portion of the skin/hair)

Cleft palate

Urogenital

Abnormal genitalia

Kidney defects

Other Heart defects (ventricular septal defect)

Single umbilical artery[4]
http://en.wikipedia.org/wiki/Patau_syndromehttp://en.wikipedia.org/wiki/Patau_syndrome


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Structural chromosome rearrangements result from

chromosome breakage with subsequent reunion in

different configuration.

Balance rearrangements the chromosome

complement is complete with no loss or gain of

genetic material.

Unbalance rearrangements the chromosomalcomplement contains an incorrect amount of

chromosome material.


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Translocations refers to the transfer of geneticmaterial from one chromosome to another.

Reciprocal translocation is formed when a breakoccurs in each of two chromosomes with the

segments being exchanged to form two new

derivative chromosomes or two nonhomologous

chromosomes exchange pieces,

Translocations


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Robertsonian translocation is a particulartype of reciprocal translocation which the

break-points are located at or close thecentromeres of two areocentricchromosomes

Translocation balanced

unbalanced


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A deletion involves loss of part of a

chromosome and results in monosomy for the

segment of the chromosome.

Wolf-Hirsch horndeletion short arm

chromosome 4

Cri du chat syndromeslosing of materialfrom the short arms of chromosomes 5


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Cri du chatsyndrome


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- A ring chromosome is a type of deletionchromosome from which both ends have beenlost, and the broken ends have rejoined to forma ring-shaped chromosome. Ring chromosomesare very rare but they have been found for allchromosomes.


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An insertion occurs when a segment of onechromosome inserted into another

chromosome.

An insertion can causes an unbalanced

chromosome complement.

Carriers of a balanced deletion-insertionrearrangement are at a 50% risk of producing

unbalanced gametesaffected offspring


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An inversion is a two-break rearrangement involving a

single chromosome in which a segment is reversed in

position, i.e. inverted.

A pericentric inversion occurs if the inversion segment

involves the centromere. A paracentric inversion occurs if it involves only one arm

of the chromosome.

Inversion is rarely cause problems in carries, unless one of

the break-points has disrupted an important gene.


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Is a presence of a chromosomal segment morethan once in the same chromosome. There is

additional of chromosome part.

The way of duplication can occur when a

broken segment from one chromosome

attached to its homologous.

It can be an unequal crossing-over, leading to

duplication and deletion.

Chromosome duplications are usually lethal.


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Types of chromosomal mutations

Inversion occurs when a piece of

chromosome breaks loose and then

rejoins in the reversed direction.

Translocation is the exchange ofchromosome pieces non

homologous pairs.

Deletion is the loose of a

chromosome piece.

Duplication occurs when the same

piece is repeated within the

chromosome


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Detection with FISH Fluorescence In Situ

Hybridisation

Prader-Willi syndrome (PWS) and

Angelman syndrome (AS) deletionchromosome 15 q12 genetic imprinting

depend on transmitting parent

T l


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Two examples are :

-Prader-Willi syndrome (PWS), a sporadically

occurring disorder associated with short stature,mild mental retardation, obesity, hyperphagia

(overeating), and hypogonadism (inadequate

gonadal function).-Angelman syndrome (AS), characterized by

severe mental retardation, microcephaly,

brachycephaly (shortness of head), seizures, andataxic (jerky) movements of the limbs and trunk.


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ISOCHROMOSOMES


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ISOCHROMOSOMES

The abnormality resulting in these

chromosomes occurs when the centromerdivides transversely instead of

longitudinally.

An isochromosome is a chromosome in

which one arm is missing and the other

duplicated. It appears to be the mostcommon structural abnormality of the X

chromosome.


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Persons with this chromosomal

abnormality are often short instature and have other stigmata of

Turner syndrome. These

characteristics are related to theloss of an arm of an X chromosome.


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fbs 4 9-chromosome aberration

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