Genetic Disorders Health Article

Genetic Disorders

Conditions with a link to the individual's genetic make-up.

Genetic disorders are conditions that can be traced to an individual's heredity. Many of these disorders are inherited and are governed by the same genetic rules that determine dimples and red hair. However, some genetic disorders result from a spontaneous mutation during embryonic development. If one parent can transmit the genetic information (in genes) that causes a child's disorder, then the disorder is said to be genetically dominant. However, if both parents lack the disorder and pass the disorder's gene to a child, then the genetic disorder is said to be recessive. But not all genetic diseases are completely determined by genes alone; some are promoted by environmental factors such as diet. Disorders that result from both genes and environment are called multi-factorial genetic diseases. In addition, some genetic disorders occur predominantly in males or females, due to the nature of the sex chromosomes, X and Y. Although many genetic diseases, such as cystic fibrosis and sickle-cell anemia, do not occur often, some more common genetic diseases include hypertension, diabetes, and certain forms of cancer.

Genetic inheritance

The principles of genetic inheritance can seem complicated to non-scientists. Basically, genetic information is organized into chromosomes in the cellular nucleus. Human cells have 46 chromosomes each—except for sperm and eggs (reproductive cells), which each have 23 chromosomes. Each person receives 23 chromosomes from their mother's egg and 23 chromosomes from their father's sperm. All but one of the 23 chromosomes are called autosomes, or non-sex chromosomes. These 22 chromosomes do not determine gender. The remaining chromosome is the sex chromosome and is either an X or a Y. Females have two Xs (XX), and males have one of each (XY). Females can only pass an X to their offspring, and males can pass either an X or a Y. Hence, the male sperm is responsible for gender selection. Because of their two X chromosomes, females can carry a disease gene on one X chromosome but not exhibit the disease since they have another X chromosome to compensate. However, males only have one X chromosome and can be affected by the same disease. Such genetic disorders are called X-linked.

The 44 autosomes have parallel coded information on each of the two sets of 22 autosomes, numbered 1 through 22, called homologous pairs. This coding is organized into genes. Individual genes are made of deoxyribonucleic acid (DNA), and code for particular proteins. Proteins play numerous critical structural and functional roles in the body. Each gene has a set locus, or position, on a particular chromosome. The genes with the same locus on corresponding chromosomes are called alleles. So, conventional terminology would describe one person as having two alleles of the same gene. Humans are called diploid organisms, because we have two alleles of each autosomal gene.