Genetics

Genetics facts
• Ova and sperm each contain 23 chromosomes.
• A fertilized cell has 46 chromosomes.
• Each chromosome contains DNA.
• DNA contains genes.
• A person receives one set of chromosomes and genes from each parent.
• More powerful gene is dominant.
• Less influential gene is recessive.

Types of genetic disorders
• Single-gene — inherited in clearly identifiable patterns. Two important inheritance patterns are:
–autosomal dominant
–autosomal recessive.
• Chromosomal — deviations in either the structure or the number of chromosomes involving the loss, addition, rearrangement, or exchange of genes.
• Multifactoral — caused by genetic and
environmental factors.

How genetic disorders develop
• Cleft lip and cleft palate — arise from interaction of several genes that originates in the second gestational month.
• Cystic fibrosis — inherited as an autosomal recessive trait; protein doesn’t function properly, which leads to dehydration and mucosal thickening.
• Down syndrome — caused by aberration of chromosome 21.
• Hemophilia — inherited as an X-linked recessive trait. Two types include:
–Hemophilia A — factor VIII deficiency
–Hemophilia B — factor IX deficiency
• Marfan syndrome — inherited as an autosomal dominant trait that causes connective tissue disease.
• Phenylketonuria — inherited as an autosomal recessive gene that leads to brain damage due to phenylalanine accumulating in blood.
• Sickle cell anemia — inherited as an autosomal recessive gene mutation, which impairs normal blood circulation.
• Tay-Sachs disease — inherited as an autosomal recessive disorder that causes lipid pigments to accumulate, destroying central nervous system cells.