Genetic Disorders
A variety of human genetic disorders follow Mendelian inheritance patterns. Some of which are autosomal (located on a non-sex chromosome), some are sex-linked, some are dominant, and some are recessive. Let's have a look.
Colourblindness (X-linked recessive): An affected individual cannot properly distinguish colours from each other. The degree of colourblindness varies greatly among those affected. It is likely to be the most common genetic disorder. Its effects are relatively minor, which is perhaps why it persists in the population in high proportions.
Cystic Fibrosis (autosomal recessive): Dysfunctional enzymes are unable to correctly produce chloride ion channels. As a result, the chloride accumulates outside cells and makes their mucous coating thicker. The buildup of mucous affects multiple organs and leads to an array of health disorders (pleiotropy). The affected individual usually dies before reaching sexual maturity.
Duchenne Muscular Dystrophy (X-linked recessive): The muscular system of affected individuals deteriorates during their childhood and teenage years, inevitably leading to death before or around their 20's.
Hemophilia (X-linked recessive): The inability to produce blood-clotting proteins makes the affected individual more susceptible to prolonged bleeding, as it takes a long time for blood clots to form. Large cuts or internal bleeding can prove to be fatal, so extra caution is required in the individual's daily activities. Interestingly, because this disease was very common among members of the European royal families, it used to be dubbed as the "Royal Disease".
Huntington's Disease (autosomal dominant): The affected individual's nervous system undergoes gradual deterioration starting from their 30's or 40's; the process is inevitably fatal. However, the individual may have reproduced before then and unwittingly passed on his/her lethal gene to their offspring.
Mitochondrial Myopathy (mitochondrial): Inherited exclusively from their mothers, individuals with this disorder have lower ATP production and are therefore more vulnerable to energy deprivation. This most commonly affects the nervous and muscular systems.
Phenylketonuria (autosomal recessive): Also abbreviated as PKU, an affected person cannot metabolism the amino acid phenylalanine. Accumulation of this can cause mental retardation. Fortunately, the adverse effects of this disease can be avoided through administering a diet low in phenylalanine.
Polydactyly (autosomal dominant): An affected individual have more than five digits on their hands or feet. These extra digits are usually not functional and are removed shortly after birth.
Sicke-Cell Disease (autosomal recessive): Caused by an incorrect amino acid in their hemoglobin proteins, people with this disease have blood cells which turn into a cresent shape when their blood oxygen levels are low; such oddly shaped cells can clump together, which clogs up blood vessels. This disease is more common among people of African descent because those with at least one allele are more immune to malaria, which gives them a selective advantage.
Tay Sachs (autosomal recessive): Brain cells cannot metabolize certain lipids because a protein involved in the pathway is dysfunctional. This is a lethal disease which leads to death in early childhood. The occurrence of this disease is disproportionately higher among Jewish families.
Colourblindness (X-linked recessive): An affected individual cannot properly distinguish colours from each other. The degree of colourblindness varies greatly among those affected. It is likely to be the most common genetic disorder. Its effects are relatively minor, which is perhaps why it persists in the population in high proportions.
Cystic Fibrosis (autosomal recessive): Dysfunctional enzymes are unable to correctly produce chloride ion channels. As a result, the chloride accumulates outside cells and makes their mucous coating thicker. The buildup of mucous affects multiple organs and leads to an array of health disorders (pleiotropy). The affected individual usually dies before reaching sexual maturity.
Duchenne Muscular Dystrophy (X-linked recessive): The muscular system of affected individuals deteriorates during their childhood and teenage years, inevitably leading to death before or around their 20's.
Hemophilia (X-linked recessive): The inability to produce blood-clotting proteins makes the affected individual more susceptible to prolonged bleeding, as it takes a long time for blood clots to form. Large cuts or internal bleeding can prove to be fatal, so extra caution is required in the individual's daily activities. Interestingly, because this disease was very common among members of the European royal families, it used to be dubbed as the "Royal Disease".
Huntington's Disease (autosomal dominant): The affected individual's nervous system undergoes gradual deterioration starting from their 30's or 40's; the process is inevitably fatal. However, the individual may have reproduced before then and unwittingly passed on his/her lethal gene to their offspring.
Mitochondrial Myopathy (mitochondrial): Inherited exclusively from their mothers, individuals with this disorder have lower ATP production and are therefore more vulnerable to energy deprivation. This most commonly affects the nervous and muscular systems.
Phenylketonuria (autosomal recessive): Also abbreviated as PKU, an affected person cannot metabolism the amino acid phenylalanine. Accumulation of this can cause mental retardation. Fortunately, the adverse effects of this disease can be avoided through administering a diet low in phenylalanine.
Polydactyly (autosomal dominant): An affected individual have more than five digits on their hands or feet. These extra digits are usually not functional and are removed shortly after birth.
Sicke-Cell Disease (autosomal recessive): Caused by an incorrect amino acid in their hemoglobin proteins, people with this disease have blood cells which turn into a cresent shape when their blood oxygen levels are low; such oddly shaped cells can clump together, which clogs up blood vessels. This disease is more common among people of African descent because those with at least one allele are more immune to malaria, which gives them a selective advantage.
Tay Sachs (autosomal recessive): Brain cells cannot metabolize certain lipids because a protein involved in the pathway is dysfunctional. This is a lethal disease which leads to death in early childhood. The occurrence of this disease is disproportionately higher among Jewish families.