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Albinism
The word "albinism" refers to a group of inherited conditions. People with albinism
have little or no pigment in their eyes, skin, or hair. They have inherited genes that do not
make the usual amounts of a pigment called melanin. One person in 17,000 has some type of albinism. Albinism affects people from all races. Most children with albinism are born to parents who have normal hair and eye color for their ethnic backgrounds. Albinism is found on the eleventh chromosome, section q, loci 14-21.
Oculocutaneous albinism involves the eyes, hair, and skin. Ocular albinism involves
primarily the eye. People with ocular albinism may have slight lightening of hair and skin
colors as well, compared to other family members. At present researchers have found 10
different types of oculocutaneous albinism, and five types of ocular albinism. Newer
laboratory research studying DNA has shown that there are numerous types of changes in
the genes of those with albinism, including within families.
The most common types of oculocutaneous albinism are called "ty-negative" and
"ty-positive". Persons with ty-negative albinism have no melanin pigmentation, and more
difficulty with vision. Those with ty-positive albinism have very slight pigmentation, and
generally less severe visual difficulties. Tests were done on the hair roots of individuals
with albinism, to tell these types of albinism apart. However, these hair tests cannot
identify types of albinism, particularly in young children, whose pigment systems are immature. Therefore hair tests are not helpful in predicting the extent of visual disability of a child. "Ty-Neg" (also called Type 1A) albinism results from a genetic defect in an enzyme called tyrosinase. Tyrosinase helps the body to change the amino acid tyrosine into pigment. The genetic defect that causes albinism in other types of albinism is unknown, but it is speculated that it involves other enzymes used to make pigment.
Albinism is passed from parents to their children through genes. For nearly all
types of albinism both parents must carry an albinism gene to have a child with albinism.
Parents may have normal pigmentation but still carry the gene. When both parents carry
the gene, and neither parent has albinism, there is a one in four chance at each pregnancy
that the baby will be born with albinism. This type of inheritance is called autosomal
recessive inheritance.
If a parent has a child with albinism, it means the parent must carry the albinism
gene. Until recently, unless a person has albinism or has a child with albinism, there was no way of knowing whether he or she carries the gene for albinism. Recently a test has been developed to identify carriers of the gene for ty-negative albinism and for other types in
which the tyrosinase enzyme does not function. The test uses a sample of blood to identify
the gene for the tryrosinase enzyme by its DNA code. A similar test can identify ty-negative or similar albinism in unborn babies, by aminiocentesis.
People with albinism have very normal lives. They play sports, have normal
intelligence, and can have babies. The only difference between normal people and albino
is that they don't have pigment in their skin.BACK TO DIRECTORY | BACK TO SUB DIRECTORY: BIOLOGY
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