Page 144 - 86 human physiology part-2

Genetics and Inheritance

Incomplete penetrates

Some genes are incomplete penetrate. Which means, unless some environmental factors are
present, the effect does not occur. For example, you can inherit the gene for diabetes, but never get the
disease, unless you were greatly stressed, extremely overweight, or didn't get enough sleep at night.

Genetic Disorders

Down Syndrome, also known as Trisomy 21, is a chromosome abnormality that effects one out of
every 800-1000 newborn babies. At birth this defect is recognizable because of the physical features
which are, almond shaped eyes, a flattened face, and less muscle tone than a normal newborn baby.
During pregnancy, it is possible to detect the Down Syndrome defect by doing amniocentesis testing.
There is a risk to the unborn baby and it is not recommended unless the pregnant mother is over the age
of thirty-five.

Any disorder caused totally or in part by a fault (or faults) of the genetic material passed from
parent to child is considered a genetic disorder. Many genetic disorders are noticed at birth, but some
may not be noticed until years later. Many children born with genetic disorders have one or many
family members with the same disorder. But sometimes a child is born with a disorder with no apparent
connection to other family members. This is because the parents may be carriers of the disorder, in that
case the parents would have no signs or symptoms. Genetic disorders are broken down into three
categories: chromosomal abnormalities, unifactorial defects and multifactorial defects.

Chromosomal Abnormalities In most cases with a chromosomal abnormality all the cells are
affected. Defects can have anywhere from little effect to a lethal effect depending on the type of
abnormality. Of the 1 in 200 babies born having some sort of chromosomal abnormality, about 1/3 of
these results in spontaneous abortion. Abnormalities usually form shortly after fertilization and mom or
dad usually has the same abnormality. Types of abnormalities: A complete extra set of chromosomes
per cell which is lethal, one of the 22 pairs of autosomal chromosomes appears in triplicate instead of a
pair which causes things like downs syndrome, and sex chromosome abnormalities which is when a
baby girl (about 1 in 2,500)is born with one x instead of two (xx) this can cause physical abnormalities
and defective reproduction systems. Boys can also be born with extra X's (XXY or XXXY) which will
cause reproductive problems and sometimes mental retardation. There is no cure for these
abnormalities. Tests are possible early in pregnancy and if a problem is detected the parents can choose
to abort the fetus.

Unifactorial Defects These disorders are rare but there is a lot of them, and they usually result in a
considerable amount of disability. They happen because of a defect in one gene or one pair of genes.
The defected gene is dominate and therefore it overrides the normal gene. There is no cure for these
defects, but they can be detected early in pregnancy.

Multifactorial Defects Most disorders fall in to this category. Multifactor disorders result in
asthma, diabetes, schizophrenia, club foot and cleft palate. These disorders are a result of many
different genes being abnormal and there is usually a history in the family. There is no cure for these
but there are surgical and medicinal options to help control them.

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