Download Chromosomal Abnormalities




Each newborn begins its existence at the point
of conception when a sperm cell from a male
unites with an ovum from a female to form a
single cell called a zygote.
At the moment of conception an individuals
characteristics are determined, these
characteristics are laid down in structures known
as chromosomes.
Chromosomes are thread like structures called
genes.

Each chromosome carries hundreds of genes
and these determine individual
characteristics such as hair, eye colour, sex,
height, body shape, size, blood group and all
aspects of development e.g. Puberty
At conception human beings receive 46
chromosome – 23 from the sperm and 23 from
the ovum. At the moment of conception the
chromosomes from the male sperm pair off with
the chromosomes from the female ovum.
 One way in which the genes on the chromosome
interact and create characteristics is determined
by dominant and recessive genes.
 A dominant gene will always express itself – this
mean that it will be seen. A recessive gene will
over powered by a dominate gene, this means
that you will not be able to see the characteristic

Dominant Gene
Recessive Gene
Dark Hair
Blonde Hair
Curly Hair
Straight Hair
Brown, hazel or green eyes
Blue or grey eyes
Blood groups A, B AB
Blood group O
High Blood Pressure
Normal Blood Pressure





22 pairs of chromosomes control the development of
most of the body. The twenty third pair of chromosomes –
the X and Y chromosomes determine the individuals sex.
A female only produces ova which contain X
chromosomes but males produce sperm which carry X or Y
chromosomes.
Half of the sperm produced carry X chromosomes and half
of the sperm produced carry a Y chromosome.
If a sperm carrying an X chromosome fertilises the ovum
first, then an XX combination will result producing a
female child. Therefore it is the male partner who
determines the sex of the child
(see attached diagram)

Sometimes at conception the resulting
zygote is genetically abnormal. In many
cases, these will be aborted spontaneously
and the woman may never know she was
pregnant and many others die later in
pregnancy. (approx 1 % of children born in
Aus has a chromosomal abnormality,
genetically inherited disorder or genetically
influenced defect).

There are conditions where abnormalities in
chromosomes are known to cause specific
syndromes or diseases

Turner’s syndrome is a random genetic
disorder that affects females. The main
characteristics include short stature and
infertility. Usually, a female has two X
chromosomes. However, in females with
Turner’s syndrome, one of these
chromosomes is missing or abnormal. The
missing genes cause the abnormalities and
features found in women with Turner’s
syndrome.





The condition may be diagnosed at various life stages:
Before birth (prenatally) - usually if an amniocentesis
has been performed or abnormalities are seen during
an ultrasound
At birth - due to certain physical features
In childhood - when the young girl doesn’t grow at a
similar rate to her peers
During the teenage years - when puberty fails to
arrive
In adulthood - during investigations for infertility.









Significant features
The most significant features of Turner’s syndrome
include: Short stature - average adult height is 143cm
(4’8”)
Infertility - due to underdeveloped ovaries
Congenital heart defects
Spatial awareness issues - problems with tasks such as
maths
Absence of menstruation (amenorrhoea)
Hearing problems.
Less significant features may include: Sunken, wide chest
with broadly spaced nipples
Extra skin on the neck
Puffy hands and feet






Turner’s syndrome is a lifelong condition. However, many
treatment options are available to help affected girls and women
reach their potential in all aspects of life. Treatment aims to
correct any physical defects and help bring about puberty. Options
include: Surgery to correct any heart defects
Growth hormone therapy to increase height
Hormone replacement therapy to trigger menstruation and the
development of secondary sexual characteristics such as breasts
Regular monitoring to check hormone levels
Regular follow-up and management of medical conditions
Treatment for the management of complications such as high
blood pressure
Assisted reproduction.
People with Down syndrome have an extra
chromosome 21 in their genetic make-up.
 Down syndrome is the most common genetic
condition and occurs in all races and cultures at
around the same rate. In Victoria, between 45 and 60
babies will be born with Down syndrome each year.
Some level of intellectual disability is the only feature
common to all people who have Down syndrome,
although a range of other features are also associated
with the condition. These include characteristic
physical features and a number of health and
developmental indications.





Down syndrome is usually recognisable at
birth and confirmed by a blood test. A doctor
can usually tell if a baby has Down syndrome
from their physical appearance.
Prenatal tests that can help to detect Down
syndrome in a foetus include:
Ultrasound scans
Amniocentesis
Chorionic villi sampling.





There are a number of physical characteristics associated with Down syndrome,
although each person with Down syndrome may display only a few of these. The
most common physical characteristics include: Eyes – nearly all people with
Down syndrome have a slight upward slant of the eyes. There can also be a small
fold of skin on the inside of the eye.
Face – this is often rounded and tends to have a flat profile.
Stature – Babies are usually smaller and weigh less at birth than others. Children
tend to grow more slowly and are commonly smaller than other children their
age. Adults with Down syndrome are commonly smaller than in the general
population.
Despite some common physical characteristics, people with Down syndrome
resemble other members of their family more than they resemble each other.
Babies with Down syndrome reach the same developmental milestones (such as
smiling, sitting up, crawling, walking, talking and toileting) as all babies, but with
some degree of delay. Speech and language development is often the area of
greatest delay.



Occurs in approx 1 in every 2500 births
Children with the disease have excessive
amounts of salt in their sweat and procude
thick mucus which block the pancreas and
lungs causing many long term problems
Their lifespan are considerably reduced



Is a blood clotting disorder where one of the
essential clotting factors is deficient.
Haemophiliacs have differing degrees of
severity.
It almost exclusively affects males and is
passed on through unaffected females who
carry the defective gene.
There is no cure and it is a lifelong condition.

Activity ‘Act Now’. Read article and answer
questions.