inheritance and genetics

The Chromosomal Hypothesis of Descent

The chromosomal hypothesis of descent recognizes genes as being responsible for the carriage of genetic information (“FAQ On Genetic Disorders,” 2017). According to the theory, chromosomes are paired particles as described by Mendelian rules, and they include genes that occupy specific locations within the chromosomes known as loci.

Based on the action of chromosomes during meiosis, the hypothesis clarified that genes are inherited. Chromosomes are thread-like structures composed of DNA, the body’s genetic substance (deoxyribonucleic acid). Per chromosome comprises a number of chromosomes, which are made up of DNA. Chromosomal abnormalities occur when there is a problem in the process of cell division.

The abnormalities can either be numerical or structural aberrations (“FAQ About Genetic Disorders,” 2017). Numerical aberrations result when there is a defect in the chromosomal division which results in a cell with an additional number of chromosomes or a deficiency in the required number e.g. trisomy, monosomy, etc. Structural aberrations occur when genetic material is lost or when its location in the chromosome is altered e.g. duplication, translocation, etc. Since chromosomes are made up of genes, the result is a deficiency or an excess of the genes contained in a chromosome. Consequently, the inheritance of the damaged chromosome results in the transmission of a disease causing gene which is mutated with an altered DNA sequence which results in a genetic disorder.

Sickle Cell Disease

Sickle cell disease is an inherited disorder which affects the oxygen carrying capacity of red blood cells (RBCs). The disease frequency is over 21% in Tropical Africa (“FAQ About Genetic Disorders,” 2017). In the US, it is common among African Americans with the sickle cell trait being prevalent amongst Hispanic Americans (“FAQ About Genetic Disorders,” 2017). It is inherited in an autosomal recessive fashion. It results from a mutation in a gene located on chromosome 11 which codes for the beta globin chain of hemoglobin.

As a result, there is a defective formation of hemoglobin molecules that makes the red blood cells to assume a sickle shape and be rigid instead of their standard round shape and flexibility through blood vessels (“FAQ About Genetic Disorders,” 2017).

Effects of Sickle Cell Disease

Sickle shaped red blood cells get trapped in small capillaries, and they fail to transport oxygen to the tissues adequately. Plugging of the microcirculation in the bones is responsible for severe bone pain among patients with the disease (“FAQ About Genetic Disorders,” 2017). Failure of oxygen delivery to the body organs results in their infarction. The death of the cells that make up the spleen, for example, causes these patients to lose the spleen’s immune function which causes them to have frequent infections (“FAQ About Genetic Disorders,” 2017). These patients have a poor health related quality of life. Infarction of the bone marrow also results in fat emboli which are transported to the lungs causing further lung infarction. Cell death in the lungs causes results ventilator failure which is lethal if not treated.

Anemia and Reduction in Lifespan

Sickled RBCs have a shorter lifespan as they are occasionally sequestered in the spleen which results in reduced hemoglobin count in these patients, called anemia. Damage to the organs and complications arising from the diseases are responsible for a reduction in the lifespan of sicklers by up to 30 years (“FAQ About Genetic Disorders,” 2017). Previously, these patients did not survive past childhood. However, due to treatment aimed at prevention coupled with better health care and aggressive medical researches, half of the patients live beyond 49 years (“FAQ About Genetic Disorders,” 2017). These patients should receive prophylaxis using folic acid and antibiotics to prevent the frequent bacterial infections coupled with regular transfusion to maintain low levels of the abnormal hemoglobin.

Reference

FAQ About Genetic Disorders. (2017). National Human Research Genome Institute (NHGRI). Retrieved 15 July 2017, from https://www.genome.gov/19016930/