Genetic disorders C.1.m. – Describe the mode of inheritance of commonly inherited disorders.

Sickle Cell anemia Point mutation Sickle cell anemia is inherited from both parents. If you inherit the hemoglobin S gene from one parent and normal hemoglobin (A) from your other parent, you will have sickle cell trait. People with sickle cell trait do not have the symptoms of sickle cell anemia. Mutations in the HBB gene cause sickle cell disease. Hemoglobin consists of four protein subunits, typically, two subunits called alpha-globin and two subunits called beta- globin. In people with sickle cell disease, at least one of the beta- globin subunits in hemoglobin is replaced with hemoglobin S. In sickle cell anemia, which is a common form of sickle cell disease, hemoglobin S replaces both beta-globin subunits in hemoglobin. In other types of sickle cell disease, just one beta-globin subunit in hemoglobin is replaced with hemoglobin S.

Down’s syndrome The three genetic variations that can cause Down syndrome include: Trisomy 21 - three copies of chromosome 21 — instead of the usual two copies — in all of his or her cells; caused by abnormal cell division during the development of the sperm cell or the egg cell. Mosaic Down syndrome - rare form of Down syndrome, children have some cells with an extra copy of chromosome 21. This mosaic of normal and abnormal cells is caused by abnormal cell division after fertilization. Translocation Down syndrome - occurs when part of chromosome 21 becomes attached (translocated) onto another chromosome, before or at conception. Children with translocation Down syndrome have the usual two copies of chromosome 21, but they also have additional material from chromosome 21 attached to the translocated chromosome. This form of Down syndrome is uncommon. Most of the time, Down syndrome isn't inherited. It's caused by a mistake in cell division during the development of the egg, sperm or embryo. Translocation Down syndrome is the only form of the disorder that can be passed from parent to child.

Examples

Turner’s syndrome a medical disorder that affects about 1 in every 2,500 girls. Although researchers don't know exactly what causes Turner syndrome, they do know that it's the result of a problem with a girl's chromosomes. Most girls are born with two X chromosomes, but girls with Turner syndrome are born with only one X chromosome or they are missing part of one X chromosome. Most cases of Turner syndrome are not inherited.

Examples

PKU an inherited disorder that increases the levels of a substance called phenylalanine in the blood, which is a building block of proteins (an amino acid) that is obtained through the diet. If PKU is not treated, phenylalanine can build up to harmful levels in the body, causing intellectual disability and other serious health problems. In the United States, PKU occurs in 1 in 10,000 to 15,000 newborns. Most cases of PKU are detected shortly after birth by newborn screening, and treatment is started promptly. Mutations in the PAH gene cause phenylketonuria. This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Examples