The focus of genetics is on the study of the impact of genetic blueprints called genotypes and the observable characteristics or phenotypes. Human and animal genes are the unit of hereditary transmission. They are encoded in the Dioxyribonucleic Acid (DNA) carried in the nucleus of each cell. The chances of sharing certain characteristics between relatives is often dubbed as biological inheritance. Parents and their children are related by 50% and grandparents by 25% and lower degree of relatedness.
Yet there are certain chances of genetic mutation or chromosome abnormality that commonly leads to genetic disorders. Most of these disorders are quite rare and may or may not be heritable or passed down from the parent to the offspring.
1. Diabetes Mellitus. This is an insulin deficiency caused by recessive genes. Though this disease can also be acquired by environmental causes such as unhealthy lifestyle, type 1 diabetes can be inherited genetically. The probability of transmission of this defect depends on several factors like the gender of the parent carrying the genes, the age when the parent developed the disease, and several other aspects.
2. Spina Bifida. A neural tube defect in which the spine remains unclosed at the bottom or a part of skull or brain is absent. This disease can affect the child's development both physically and mentally. Its risk can possibly be lowered by adding folic acid to the mother's nutritional intake before and during pregnancy. And for the infected patients, there are several surgical procedures to fix the gap.
3. Huntington chorea. A lethal disease characterized by the degeneration of the nervous system caused by dominant chromosomes. This disorder induces involuntary muscle contractions, distress, and notable changes in personality. It usually shows up at early adulthood, can start at any age, and affects both gender.
4. Tay Sachs disease (TSD). This is an enzyme disorder that leads to the brain incapacitance to breakdown particular fats. The Tay Sach gene can only be acquired by the offspring if both parents carry the genes and the chances whether the child will have the disease or not varies greatly. Children born with this disease usually die within three years after birth.
The following types of genetic disorder are due to recessive chromosomes:
5. Sickle-cell anemia. This is often carried by recessive genes. Patients with this disease have red blood cells with unusual shape caused by abnormal hemoglobin and multiply with oxygen insufficiency.
6. Phenylketonuria (PKU). The existence of two recessive genes. The liver enzyme bound to break down excess phenylalanine generates poison that impairs the nervous system and leads to mental retardation. For a child to be affected by this disorder, both parents must be carriers of the mutated gene/s. This disorder can be detected easily at birth and though it can't be completely cured, the effects can be minimized through a controlled diet and medication.
7. Muscular Dystrophy (MD). This is a degenerative disorder linked to recessive genes and characterized by gradual loss of strength and inability to walk. There are no known cure for this disease yet, but there are several procedures and programs that help MD patients to live better lives.
The next chromosomal disorders are not genetically related. These are associated with chromosomal failure caused by erroneous divisions and synthesis during meiosis.
8. Fragile X syndrome. Distorted or broken chromosomes more frequent in males than females. Mental retardation is usually manifested during adolescence. But there are physical and emotional signs shown at childhood.
9. XYY syndrome. A disorder that affects males caused by an extra Y chromosome. Men with this disease are likely to have exaggerating height. There were no recorded cases of mental retardation in people with this disease, but some of them had learning difficulties.There were some instances of aggression linked to this disease but not evident enough.
10. Cri-du chat syndrome. Also known as chromosome 5p deletion syndrome. Characterized by cat-like cries, facial anomalies, gastrointestinal defects, serious mental retardation, and throat malformation. Because of these physical defects, patients had eating difficulties that results to malnutrition and therefore worsening the situation.
11. Prader Willi syndrome. Removal in the long arm chromosome 15 between band of Q 11 and 13. Usual indications are poor sucking reflex, uncontrollable appetite, poor sexual development, peculiar facial form, mental impairment, and behavioral problems. Because of their compulsive eating habits and poor muscle tone, patients are very much likely to eat and sleep excessively.
12. Down syndrome. Caused by the presence of all or part of and extra 21st chromosome (Trisomy, 21); known as Mongolism, is associated with delayed physical growth, a vast skull that is flat in the back, narrow and tilted eyes, fissured tongue, mental incapabilities, and some congenital heart defects. This is the most typical type of disease related to chromosomal error.
13. Turner Syndrome. A female disorder characterized by the absence of X chromosomes (45 X); common features are short and wide chest, underdeveloped secondary traits, narrowing aorta, and amenorrhea. Other than alleviating the symptoms, there are no known medicine or medical procedure to cure TS. However, this disease doesn't cause serious mental impairment except for spatial recognition.
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