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SUBMITTED BY:
Phumelele Ndlovu

What is a chromosome?
 A chromosome is…

 A very long DNA molecule and associated
proteins that carries portions of the hereditary
information of an organism.

 They are composed of DNA and proteins that
are located within the nucleus of our cells.
Chromosomes determine everything from hair
color and eye color to sex.

Chromosomes are described
with the following categories:
 Metacentric
 centromere is median or near median
 chromosome has two well defined arms with
a length ratio varying from 1:1 to 2.5:1
 Submetacentric
 A chromosome whose centromere lies
between its middle and its end but closer to
the middle.

with the following
categories:
 Acrocentric
 centromere is close to one end of the
chromosome
 one arm is substantially smaller than the
other and the arm ratio ranges from 3:1 to
10:1
 Telocentric
 centromere is a strictly terminal entity and the
chromosome is one armed

with the following
categories:

Chromosomes are always
arranged with the short arm
on top:
 Short arm is labeled
P (French for petit)
 Long arm is labeled
Q

Human chromosomes are
divided into 7 groups & sex
chromosomes
 A 1-3 Large metacentric 1,2 or submetacentric
 B 4,5 Large submetacentric, all similar
 C 6-12, X Medium sized, submetacentric -
difficult
 D 13-15 medium-sized acrocentric plus
satellites
 E 16-18 short metacentric 16 or
submetacentric 17,18
 F 19-20 Short metacentrics
 G 21,22,Y Short acrocentrics with satellites. Y
no satellites.

Genetics 120315105011-phpapp01

Karyotype
 An individual's
collection of
chromosomes.
 It refers to the
complement of
chromosomes either
at the species level, or
of individuals.
 Is used to look for
abnormal numbers or
structures of
chromosomes.

Karyotyping
 Also known as Karyotype Test
 A laboratory technique that produces an
image of an individual's chromosomes.
 Is a test to identify and evaluate the
size, shape, and number of
chromosomes in a sample of body cells.
 Extra, missing, or abnormal positions of
chromosome pieces can cause problems
with a person's
growth, development, and body
functions.

Why Karyotyping is
done:
 Determine whether the chromosomes of an
adult have an abnormality that can be
passed on to a child.

 Determine whether a chromosome defect is
preventing a woman from becoming
pregnant or causing miscarriages.

 Determine whether a chromosome defect is
present in a fetus.

Why Karyotyping is
done:
 Determine whether chromosomal problems may
have caused a fetus to be stillborn.

 Determine the cause of a baby's birth defects or
disability.

 Help determine the appropriate treatment for
some types of cancer.

 Identify the sex of a person by determining the
presence of the Y chromosome. This may be done
when a newborn's sex is not clear.

Chromosomal
Aberrations
 Sex chromosome abnormalities occur as a result of
chromosome mutations brought on by mutagens
(like radiation) or problems that occur during
meiosis.

 One type of mutation is caused by chromosome
breakage. The broken chromosome fragment may
be deleted, duplicated, inverted, or translocated to
a non-homologous chromosome.

 Another type of mutation occurs during meiosis
and causes cells to have either too many or not
enough chromosomes.

Klinefelter Syndrome
(XXY) syndrome, also known as the XXY
 Klinefelter
condition, is a term used to describe males who have an
extra X chromosome in most of their cells. Instead of
having the usual XY chromosome pattern that most
males have, these men have an XXY pattern.

 Klinefelter syndrome is named after Dr. Henry
Klinefelter, who first described a group of symptoms
found in some men with the extra X chromosome.

 Scientists believe the XXY condition is one of the most
common chromosome abnormalities in humans.
About one of every 500 males has an extra X
chromosome, but many don’t have any symptoms.

Klinefelter Syndrome
(XXY)
 Common Physical Characteristics:
 small testicles and penis
 Breast enlargement
 sterility
 infertile

Metafemale (XXX)
 A metafemale is a woman who has an extra X
chromosome. It is a condition that is commonly
referred to as Triple X Syndrome and it is thought
to affect around 1 in every 1000 women.

 Triple X Syndrome results during division of a
parent's reproductive cells.

 In most cases there will be no unusual physical
features or medical problems resulting from Triple
X Syndrome. This is because in all female cells
there is only one active X chromosome at any one
time.

Metafemale (XXX)
 Generally normal due to Barr Bodies
 Tall stature
 Behavioral problems
 Clumsiness and poor co-ordination
 Wide-set eyes
 Reduced muscle tone
 Ovarian failure

Turner Syndrome (XO)
 Turner syndrome is a chromosomal condition that
alters development in females.

 This condition occurs in about 1 in 2,500 female
births worldwide, but is much more common
among pregnancies that do not survive to term
(miscarriages and stillbirths).

 Turner syndrome is a chromosomal condition
related to the X chromosome

 Researchers have not yet determined which genes
on the X chromosome are responsible for most
signs and symptoms of Turner syndrome.

Turner Syndrome (XO)
 extra skin on the neck (webbed neck)
 puffiness or swelling (lymphedema) of the
hands and feet
 skeletal abnormalities
 heart defects
 kidney problems

Jacobs Syndrome (XYY)
 Jacob's syndrome is a rare chromosomal
disorder that affects males. It is caused by the
presence of an extra Y chromosome. Males
normally have one X and one Y chromosome.
However, individuals with Jacob's syndrome
have one X and two Y chromosome.
 Males with Jacob's syndrome, also called XYY
males.
 Jacob's syndrome occurs when a male inherits
two Y chromosomes from his father instead of
one. He is an XYY male. Most males are XY.
 The exact cause of the XYY aberration is
unknown.

Jacobs Syndrome (XYY)
 With uncontrolled temper and antisocial
 Severe acne problems
 Tall and thin
 High testosterone levels

Autosomal Aberrations
 Syndrome or disorder of interest is
pertaining to a chromosome that is NOT
a sex chromosome, either X or Y but of
body chromosomes.

Down Syndrome
(Trisomy 21)
 Down syndrome (also called Trisomy 21) is
a genetic disorder that occurs in
approximately 1 of 800 live births.

 Down syndrome is named after Doctor
Langdon Down, who in 1866 first described
the syndrome as a disorder.

 It is the leading cause of cognitive
impairment.

Down Syndrome
(Trisomy 21)
 Oblique eye features
 mild to moderate learning disabilities
 Developmental delays
 Characteristic facial features,
 Low muscle tone in early infancy.
 Epicanthal fold
 Simian crease

Edward Syndrome
(Trisomy 18)
 The Edward's syndrome, which got its
name after the famous doctor, Dr. John
Edward.
 A genetic chromosomal disorder caused by
an error in cell division resulting on
additional third chromosome 18.
 Edward's syndrome, a result of one of the
genetic disorders and most common after
Down syndrome, occurs in approximately
one among 3000 to 6000 births.

Edward Syndrome
(Trisomy 18)
 Upturned nose
 Growth Deficiency
 Abnormal skull shape and facial features
 Clenched hands
 Rocker bottom feet
 Cardiac and renal abnormalities

Patau Syndrome
(Trisomy 13)
 Patau syndrome, also referred to
as, 'Trisomy 13.
 A form of genetic disorder in which all or a
portion of the person's chromosome
thirteen appears three times instead of
twice in the cells of their body.
 The extra material interferes with the
person's regular process of
development, which leads to severe
intellectual disability and physical
abnormalities in a number of parts of their
body.

Patau Syndrome
(Trisomy 13)
 Polydactyl and cleft palate
 Low-set ears
 Scalp defects
 Clenched hands
 Small lower jaw
 Mental retardation
 Single palmar crease
 Undescended testicle
 Skeletal abnormalities
 Close-set eyes - eyes may actually fuse together

Angelman Syndrome
 A neuro-genetic disorder that it is usually
caused by deletion or inactivation of genes on
the maternally inherited chromosome 15 while
the paternal copy, which may be of normal
sequence, is imprinted and therefore silenced.
 AS is named after a British pediatrician, Dr.
Harry Angelman, who first described the
syndrome in 1965.
 People with AS are sometimes known as
"angels", both because of the syndrome's name
and because of their youthful, happy
appearance.

Angelman Syndrome
 Intellectual and developmental delay
 Sleep disturbance
 Seizures
 Jerky movements (especially hand-flapping)
 Frequent laughter or smiling
 Usually a happy demeanor.

Angelman Syndrome

Note: The deletion in
Chromosome 15 is so small
and is almost not visible

Prader–Willi syndrome
 Is a rare genetic disorder in which seven genes
(or some subset thereof) on chromosome 15 (q
11–13) are deleted or unexpressed (chromosome
15q partial deletion) on the paternal
chromosome.

 It was first described in 1956 by Andrea Prader
(1919–2001), Heinrich Willi (1900–1971), Alexis
Labhart (1916), Andrew Ziegler, and Guido
Fanconi of Switzerland.

Prader–Willi syndrome
 Low muscle tone
 Short stature
 Incomplete sexual development
 Cognitive disabilities
 Problem behaviors
 Chronic feeling of hunger that can lead to
excessive eating and life-threatening obesity

-The chromosome's structure is altered

Structural Aberrations
 Deletions
 A portion of the chromosome is missing or deleted.
Known disorders in humans include Wolf-
Hirschhorn syndrome, which is caused by partial
deletion of the short arm of chromosome 4; and
Jacobsen syndrome, also called the terminal 11q
deletion disorder.
 Duplications
 A portion of the chromosome is duplicated, resulting
in extra genetic material. Known human disorders
include Charcot-Marie-Tooth disease type 1A which
may be caused by duplication of the gene encoding
peripheral myelin protein 22 (PMP22) on
chromosome 17.

 Translocations
 When a portion of one chromosome is
transferred to another chromosome. There are
two main types of translocations. In a reciprocal
translocation, segments from two different
chromosomes have been exchanged. In a
Robertsonian translocation, an entire
chromosome has attached to another at the
Centromere - in humans these only occur with
chromosomes 13, 14, 15, 21 and 22.
 Inversions
 A portion of the chromosome has broken
off, turned upside down and
reattached, therefore the genetic material is
inverted.

 Insertions
 A portion of one chromosome has been
removed from its normal place and inserted into
another chromosome.
 Rings
 A portion of a chromosome has broken off and
formed a circle or ring. This can happen with or
without loss of genetic material.
 Isochromosome
 Formed by the mirror image copy of a
chromosome segment including the centromere.

Wolf-Hirschhorn
Syndrome
 A syndrome is due to a specific
chromosomal deletion which is the cause of
typical facial features and developmental
delays.
 The anomalies are due to the lack of
chromosomal material from the top of one
of the number 4 chromosomes.
 This results in missing genes which
account for the anomalies. The degree of
deletions and scope of symptoms vary
widely and reflect the amount of genetic
material that is missing.

Wolf-Hirschhorn
Syndrome
 Short philtrum
 Small head size (microcephaly)
 "Greek helmet like" nose shape
 Wide spaced eyes (hypertelorism)
 Mental retardation

Cri-du-chat Syndrome
 Also known as chromosome 5p deletion
syndrome, 5p minus syndrome or Lejeune’s
syndrome
 A rare genetic disorder due to a missing part of
chromosome 5. Its name is a French term (cat-
cry or call of the cat) referring to the
characteristic cat-like cry of affected children.
 It was first described by Jérôme Lejeune in
1963. The condition affects an estimated 1 in
50,000 live births, strikes all ethnicities, and is
more common in females by a 4:3 ratio.

Cri-du-chat Syndrome
 Excessive drooling
 Feeding problems because of difficulty
swallowing and sucking.
 Low birth weight and poor growth
 Severe cognitive, speech, and motor delays
 Behavioral problems such as
hyperactivity, aggression, tantrums, and
repetitive movements.
 Unusual facial features which may change over
time

Cat eye Syndrome
 A rare condition caused by the short arm (p) and a
small section of the long arm (q) of human
Chromosome 22 being present three (trisomic) or
four times (tetrasomic) instead of the usual two
times.
 The term "Cat Eye" syndrome was coined because of
the particular appearance of the vertical colobomas
in the eyes of some patients.
 However, over half of the CES patients in the
literature do not present with this trait. There is no
significant reduction in life expectancy in patients
who are not afflicted with one of CES' life
threatening abnormalities.

Cat eye Syndrome
 Iris coloboma
 Anal atresia (abnormal obstruction of the anus)
 Unilateral or bilateral iris coloboma (absence of
tissue from the colored part of the eyes)
 Palpebral fissures (downward slanting openings
between the upper and lower eyelids)
 Preauricular pits/tags (small depressions/growths of
skin on the outer ears)
 Cardiac defects (such as TAPVR)
 Kidney problems (missing, extra, or underdeveloped
kidneys)
 Short stature
 Scoliosis/Skeletal problems

Velo-Cardio-Facial
Syndrome
 Velocardiofacial syndrome is a genetic disorder
that is present from birth and can be characterized
by a variety (over thirty) different signs and
symptoms.

 Although the gene or genes that cause
velocardiofacial syndrome have not been
identified, most of the children who have been
diagnosed with this syndrome are missing a small
part of chromosome 22.

Velo-Cardio-Facial
Syndrome
 cleft palate (opening in the roof of the
mouth)
 heart defects, certain facial features
 minor learning problems
 speech and feeding problems

Charcot-Marie-Tooth
Disease
 Also known also as Morbus Charcot-Marie-
Tooth, Charcot-Marie-Tooth
neuropathy, hereditary motor and sensory
neuropathy (HMSN), hereditary sensorimotor
neuropathy (HSMN), or peroneal muscular
atrophy.
 An inherited disorder of nerves (neuropathy)
that takes different forms.
 It is caused by duplication of the gene
encoding peripheral myelin protein 22
(PMP22) on chromosome 17.

Charcot-Marie-Tooth
Disease
 Foot drop which is the dropping of the
forefoot due to weakness, damage to the
peroneal nerve or paralysis of the muscles
in the anterior portion of the lower leg.
 Scoliosis
 Malformed hip sockets
 Gastrointestinal problems can be part of
CMT, as can chewing, swallowing, and
speaking (as vocal cords atrophy).

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Genetics 120315105011-phpapp01

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