Common Forms of Inheritance
Each child has two copies of every gene in its body: one from the father and one from the mother. The genes that make each pair containing instructions for a dominant or recessive trait. Sometimes genes are altered for some reason and there is a medical condition.

Autosomal dominant
If a parent has the gene for an autosomal dominant condition, there is a probability of 50 percent (a probability of two) that the child has the same condition. Dominant disorders tend to be quite variable, with symptoms that can be null or severe.

Some conditions transmitted by autosomal dominant inheritance are:

  • High cholesterol Family
  • Huntington’s disease , a progressive nervous system disorder
  • Some forms of glaucoma , which causes blindness if not treated
  • Polydactyly: existence of extra fingers on the hands or feet
  • Marfan syndrome , which affects the connective tissue (the connective tissue supports and connects the body’s structures , tendons , ligaments , cartilage and bone are examples of connective tissue)

Autosomal recessive
If both parents carry the same recessive gene that can cause a birth defect there is a likelihood of four of each of their children inherit the problem. If only one parent transmits the gene for the disorder, the normal gene received from the other parent will prevent the condition to manifest.

Autosomal recessive disorders are often severe and can lead to premature death. Some conditions transmitted by autosomal recessive inheritance are:

  • sickle cell anemia , a blood disease that primarily affects African-Americans and Hispanic
  • Tay -Sachs disease , which causes mental retardation and death , mainly in people of Eastern European Jewish or French Canadian
  • Cystic fibrosis, a disorder of the lungs and digestive system that primarily affects Caucasian people of northern European descent
  • Phenylketonuria (PKU ), a metabolic disorder that primarily affects Caucasian

Inheritance X -linked recessive
The X and Y chromosomes that determine sex. Normal women have two X chromosomes and males one X and one Y chromosome A disorder caused by an abnormal gene on one chromosome known as X -linked disorder X -linked or sex.

A seemingly normal mother with an abnormal gene on one of her X chromosomes has a probability of 50 percent (one out of two) to communicate it to his son. A woman who inherits an X chromosome with a gene for a sex -linked disorder usually has no symptoms of the disease since it has an X chromosome reserve with a normal copy of the same gene. However, men who inherit an X chromosome with a gene for a sex-linked disease have no second X chromosome reserves and, therefore, suffer from the disease.

Some conditions that are transmitted through inheritance X-linked recessive are:

  • Hemophilia, in which the blood lacks a substance needed for blood clotting
  • Colorblindness of the red and green
  • Duchenne muscular dystrophy, which causes muscle weakness and death

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