Chromosomal aberrations

Submitted by:

Claudette Dabu

Lester Santos

AAPD2F

Chromosomal aberration

A

ny change in the normal structure or number of

chromosomes; often results in physical or mental

abnormality.

Euploidy

N

ormal complement of chromosomes, which in

humans, is 2n where n is the haploid number

Chromosomal disorders

Aneuploidy

I

t is an abnormal number of chromosomes.

A

n extra or missing chromosome is a common cause of

genetic disorder

I

t occurs during cell division when the chromosome do not

separate properly between the two cells

Kinds of anueploidy

M

ONOSOMY- missing one chromosome from a pair (2n-1)

T

RISOMY- presence of three copies of a chromosome (2n+1)

T

ETRASOMY- presence of four copies of a chromosome (2n+2)

P

ENTASOMY- presence of additional three chromosomes of one type

in an otherwise diploid cell (2n+3)

klinefelter

I

t is a chromosomal condition that affects male sexual

development. Males with this condition typically have small

testes that do not produce enough testosterone, which is the

hormone that directs male sexual development before birth and

during puberty.

M

ost males with this syndrome have one extra copy of the X

chromosome in each cell.

I

n addition to affecting male sexual development,

variants of Klinefelter syndrome are associated with

intellectual disability, distinctive facial features,

skeletal abnormalities, poor coordination, and severe

problems with speech.

Down syndrome

I

t is also called Trisomy 21, it is a condition in which extra

genetic material delays in the way a child develops, both

mentally and physically.

C

ommon physical signs include:• Decreased muscle tone at birth• Flattened nose• Separate joints between the bones of the skull• Small ears, mouth• Upward slanting eyes; wide short hands with short fingers

Turner syndrome

I

t is a genetic disorder that affects a girl’s development.

The cause is a missing or incomplete X chromosome.

Girls who have it are short, and their ovaries don’t work

properly. Most are infertile. They are at risk for health

difficulties such as high blood pressure, kidney

problems, diabetes, cataracts, osteoporosis, and thyroid

problems.

O

ther physical features:• Short “webbed” neck with folds of skin from tops of

shoulders to sides of neck• Low hairline in the back• Low set ears• Swollen hands and feet

Patau syndrome

I

t is also called Trisomy 13

T

he extra copy of chromosome 13 in Patau syndrome

causes severe neurological and heart defects which

make it difficult for infants to survive.

P

hysical characteristics:• Extra fingers or toes (polydactyl)• Deformed feet (Rocker-bottom feet)• Small head (microcephaly)• Failure of the brain to divide into halves during gestation• Small eyes• Absent or malformed nose• Cleft lip/ cleft palate• Heart defects• Kidney defects

Cri-du-chat syndrome

I

t is a chromosomal condition that results when a piece of

chromosome 5 is missing. Infants with this condition often have

a high-pitched cry that sounds like that of a cat.

T

he disorder is characterized by intellectual disability and

delayed development, small head, low birth weight, weak muscle

tone in infancy, widely set eyes, low set ears, small jaw, rounded

face.

Edwards syndrome

A

lso called Trisomy 18

I

t is a chromosomal condition associated with sever intellectual

disability and abnormalities in may parts of the body.

O

ften have a low birth weight, small abnormally shaped head, small

jaw and mouth, clenched fists with overlapping fingers, heart

defects, and abnormalities of other organs.

Cat eye syndrome

A

rare condition caused by the p arm and a small section of

the q arm of chromosome 21 being present three or four

times instead of the usual two times.

T

he “Cat Eye” syndrome was coined because of the

particular appearance of the vertical colombas in the eyes

of some patients.