Term Papers on Birth Defects

Term Paper Title	Birth Defects
# of Words	753
# of Pages (250 words per page double spaced)	3.01

Birth Defects

Birth defects, or congenital
malformations, are the faulty formation of
structures or body parts present at birth.
Sporadic, hereditary, or acquired defects may be
immediately observed or may become manifest
later in life; they may be visible on the body
surface or present internally. Birth defects may be
life threatening and require surgical correction, or
they may interfere with function or appearance. It
is estimated that about 3% of all children are born
with major defects; minor defects or variations are
estimated to occur in 10% to 15% of births.
Malformations may be single or multiple. Multiple
malformations that occur in a regular recognizable
pattern are referred to as syndromes--for
example, the FETAL ALCOHOL SYNDROME
sometimes observed in infants of mothers who
drank heavily when pregnant. Birth defects may
result from the action of genes, chromosomes, or
the environment on the developing fetus, but often
the cause cannot be determined. Inherited Defects
Abnormal genes cause a significant number of
different birth defects. Some can be identified as a
single-gene disorder that is inherited in a simple
Mendelian mode, that is, either a dominant or a
recessive pattern. For example, lobster claw
deformity of the hands and feet (split hands or
feet) is inherited and results from the effect of a
single dominant gene. A person who has this
deformity runs a 50% risk (1 in 2) of bearing
offspring who will inherit the gene and will
therefore also be affected. Autosomal recessive
inheritance and X-linked recessive inheritance
account for the other forms of single-gene
inheritance that cause birth defects. In cases of
autosomal recessive inheritance, both parents are
normal but each carries a silent, or recessive, gene
that, if matched in an offspring, causes the birth
defect. Because both parents are so-called
carriers (heterozygotes) of the same abnormal
gene, they run a 25% risk (1 in 4) of having a child
with the birth defect caused by that particular
gene. Examples of birth defects inherited in this
autosomal recessive manner are TAY-SACHS
DISEASE and SICKLE-CELL ANEMIA. In
cases of X-linked recessive inheritance the
abnormal gene is located on the X chromosome.
The normal mother has two X chromosomes, one
of which carries the gene for the abnormal
condition; but if her son inherits her X
chromosome with the abnormal gene, he will be
affected with the condition. HEMOPHILIA is
inherited in this matter. Multifactorial Defects
Many common birth defects do not occur in a
pattern that indicates simple Mendelian
inheritance. They seem to result from an
interaction of genes and the environment, including
the intrauterine environment, and each factor
includes a number of different hereditary and...

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