Chris Grounds CCS
Biology II 10/3/00
Earth?s inhabitants have populated all of the regions of the world, discovered places never dreamed of, and have advanced beyond normal understanding, while man can still be conquered by an object which is immeasurably small. While man has been so busy trying to find a way to get rid of all pain and suffering, he has finally discovered that there are things that cannot be stopped. This relentless phenomenon is called a genetic disorder. A genetic disorder by definition is a medical condition caused by an error in a person?s genetic material . Genetic disorders play an important role in life and must be learned about if humans are going to survive.
To fully comprehend genetic disorders, one must understand the basics of genetics and it?s diseases. Some genetic disorders can already be seen at birth, while others don?t show up until in childhood or adult life. In these instances it is usually harder for them to be identified. These disorders aren?t always serious though, they may cause such a small disease as color blindness or go all the way up to death. There have already been 9000 genetic disorders found and researched by scientists. What makes genetic disorders really stand out is their complexity. Genetic disorders are known for affecting at least more than 3 different parts of the body, thus making them harder to cure and more of a threat.
All genetic disorders involve genes of the nuclei in some way or fashion. Genes are made of DNA, Deoxy Ribo-Nucleic Acid, and are arranged specifically on chromosomes. Chromosomes are tight coils of chromatin, which is made up of DNA. Chromosomes are an instrumental factor in genetic disorders. Chromosomes are made up of a ?p? arm and a ?q? arm. ?P? stands for petite or short, while ?q? is the next letter in the alphabet, it means long. Located in the center of the chromosome is something called a centromere, pinched portion of the chromosome that connects both arms of the chromosome. Normal humans have 46 chromosomes, which means that they have 23 pairs of chromosomes. 44 of these chromosomes are normal, while that last two determine the gender of the individual. To understand chromosomes, a technique was made that could stain chromosomes so that they could be seen. After this innovation was discovered, a new technique rose called banding. There are many variations to chromosome banding. Examples of such variations are Q banding, G banding, and C banding. Each different form uses a separate medium to show the bands of the chromosome. The bands of chromosomes act as fingerprints, and allow humans to organized and recognize them. A visual organized representation of chromosomes is called a karyotype. There are many different variations of karyotypes which go accordingly with the different chromosomes and genetic codes. A spectral karyotype distinguishes between chromosomes by color, while a classic one separates by pairing off in chronological order.
There are four main areas of genetic disorders, Chromosomal, Single-gene disorder, multifactorial, and Mitochondrial. Chromosomal disorders affect approximately seven out of every 1,000 infants. A chromosomal disorder is brought about when a person has too many or too few chromosomes, or when there is a change in the structure of a chromosome. Euploidy is the condition of having a normal number of structurally normal chromosomes. A euploid of any sort has the correct form of product. Aneuploidy is the condition of having less than or more that the normal diploid number of chromosomes. This condition is associated justly with cell genetic abnormalities. There are two common forms of aneuploidy, Monosomy and Trisomy. A monomy is the lack of a pair of chromosomes. An example of a disease caused by a monomy is Turner?s Syndrome. Turner?s syndrome is a monomy of the ?x? chromosome. Instead of having two ?x? chromosomes there is only one functioning chromosome. A Trisomy is having three chromosomes of a specific type. A common trisomy is trisomy 21. Trisomy 21 is Down?s Syndrome. The 21?st pair of chromosomes has three instead of just two. There is another type of aneuploidy called triploidy. A triploid has three of each chromosome. Most, if not all, individuals that are born as triploid are either dead already, or will die very soon. A chromosome deletion is when part of a chromosome has been either deleted or broken off and lost. A deletion may get rid of an entire chromosome, part of one, or a band. An example of a disease caused by a chromosome deletion is cri-du-chat. A chromosome duplication is when a section of a chromosome is duplicated. This is also called a partial trisomy. A new form of chromosome deformation has been discovered. It is called a chromosome ring. This is when one end of the chromosome may stick to the other and form a circle which will cause problems when cell division takes place. Another way this could happen is a form of cell fusion. A chromosomal translocation is when a portion of a chromosome switches with another portion and thus making a mixture of two different chromosomes. There are two different types of translocation, balanced and unbalanced. An unbalanced translocation is more dangerous because there is probably three pieces of one chromosome, and only one of another. On the other hand, a balanced translocation shouldn?t have that much trouble, because all of the genetic material is there, however if the individual seeks to have children, then there are certain risks involved. A chromosome inversion is when there are two breaks in one chromosome, then the two pieces are switched around, and put back into the chromosome. There are two different types of inversions. One is pericentric inversion, which means if the inverted area includes the centromere. If the inverted area does not include the centromere, then it is called a paracentric version. Chromosomal disorders are an important part of genetic disorders.
Single Gene disorders, inborn errors of metabolism or Mendelian disorders, are caused by non-working genes. Every gene has information used by cells used to manufacture a specific protein, or a component of a protein. A mistake in the DNA may cause a person?s cells to fail to produce the correct number of a certain protein, or to make the protein wrong. These kinds of proteins will most likely not work correctly. In some instances, a faulty gene may have a dominant effect, in which the person has one faulty gene and one good one, and will have a disorder show up. If it has a recessive effect, then nothing will happen unless the individual gets two of those genes. Have of all single gene disorders are autosomal dominant. That means that the messed up gene is carried on an autosomal chromosome, a normal chromosome numbered one to forty four and excluding the sex chromosomes. People with this disorder have a fifty percent chance of continuing their disease onto their children. An example of this disorder would be Huntington?s Disease, which doesn?t show up until an individual is thirty or forty. There are also autosomal recessive disorders. This happens when a person has two faulty copies of the gene. These parents would have a 25 percent chance of passing it on to their children if they were both carriers of this disorder. An example of this disorder is cystic fibrosis. This disorder affects many different regions of the body. Some single gene disorders are not entirely dominant or recessive and are just called co-dominant. An example of this disorder is Sickle Cell Anemia. This is when the red blood cells are misshapen and don?t carry enough oxygen and don?t move as fast through the vessels.
There is a single gene disorder which is x-linked. These stem from a gene located only on the x chromosome. Males have a better chance of receiving these disorders than women. An example of this disease is Hemophilia, where the body can?t clot blood or produce platelets.
Multifactorial disorders are caused by gene variations as well as a person?s environment. An example of a multifactorial disorder is neural tube. This is when the structure that develops the spinal chord and brain is damaged. Some diseases that run in families, but aren?t obviously inherited are thought to be multifactorial disorders. An example of one of these diseases is coronary heart disease. In these cases a person is predisposed to get the disease, but a change in lifestyle could affect it and stop it from happening.
Mitochondrial disorders result from problems with the mitochondria?s DNA inside the cell. Sperm and eggs have mitochondria, but a sperm only gives it?s nucleus to the egg, so mitochondrial disorders are passed solely by the mother. Both males and females may be affected, but an affected male will not pass it on to his children. Conditions involving mitochondrial inheritance are rare, though one example is called Leber?s hereditary optic neuropathy. This is a vision disorder that shrinks the optic nerve.
There are many different ways to tell if someone may have a genetic disorder, these techniques are called genetic screening. A test that can be done at the earliest part of life is called the pre-implantation diagnosis, which works with in vitro fertilization, joining a sperm and egg outside of a woman?s body. Physicians can remove a cell from the embryo to test for a disorder. Prenatal screening, screening done during pregnancy, is used to identify fetuses that run a risk of getting a genetic disorder. This is done by testing the woman?s blood for specific substances known to be involved in genetic disorders. Genetic screening of newborn children is necessary to see if the child may have a disorder that must be dealt with immediately. If diagnosed early enough, an infant may be treated and have a chance of being cured. Carrier screening is done to see if a couple are carriers of a disorder before they have children. There are many different races that run different risks of different disorders. Some receive the disorder more readily. A family history screening helps identify healthy individuals who may have a risk of getting a disorder, or passing it along to their children. A doctor takes information from as far as three generations back to produce a pedigree. The pedigree is able to help identify the risks of genetic disorders. There is a new form of detection tool in genetics right now, it is called FISH. This stands for fluorescent in situ hybridisation. These methods work well and are becoming more popular in detecting disorders.
It is necessary the genetic disorders must continue to be studied if man is ever to have a chance against such a formidable enemy. Currently there are no permanent cures for genetic disorders. In order to find these cures, there still must be considerable leaps in the fields of genetic screening and genetic therapy. There is no way that people can just stumble upon something in such a complex subject as genetic disorders. Although people still die as a result of man not knowing enough, there is the fact that he never will. No matter how hard man tries, he can never fully understand something so complex and perfect as genetics.