Human Genetics and Disorders

47, XYY is not inherited, but usually occurs as a random event during the formation of sperm cells. An incident in chromosome separation during anaphase II (of meiosis II) called non disjunction can result in sperm cells with an extra copy of the Y-chromosome. If one of these atypical sperm cells contributes to the genetic makeup of a child, the child will have an extra Y-chromosome in each of the body's cells.

Sickle-cell disease is a hereditary blood disorder, characterised by red blood cells that assume an abnormal, rigid and sickle shape. Sickling decreases the cells' flexibility and results in a risk of various life-threatening complications. This sickling occurs because of a mutation in the haemoglobin gene.

Osteopetrosis is an extremely rare inherited disorder whereby the bones harden and become denser. It can cause bones to dissolve and break.

Osteogenesis imperfecta is a congenital bone disorder characterised by brittle bones that are prone to fracture. People with OI are born with defective connective tissue, or without the ability to make it, usually because of a deficiency of Type-I collagen.

Fluctuation analysis given by Salvador Luria and Max Delbruck is associated with mutation rate. Fluctuation analysis shows that resistance in bacteria occurs before exposure to the phage and argues against the adaptation hypothesis of mutations.

The degenerative process in which nucleus becomes shrunken and stains deeply is referred to as nuclear pyknosis.

Correct answer. Deficiencies of the various enzymes and transporters involved in the urea cycle can cause urea cycle disorders. Deficiency of the mitochondrial ornithine transporter causes hyperornithinemia, hyperammonemia and homocitrullinuria syndrome.

Huntington's chorea, Phenylketonuria (PKU), and Tay-Sachs disease are all genetic disorders caused by inherited mutations in specific genes. Rheumatic heart disease, however, is an acquired condition resulting from rheumatic fever - itself a complication of untreated or poorly treated streptococcal throat infection caused by Group A Streptococcus bacteria. It is not inherited genetically but develops after infection.

Fibrous dysplasia is an autosomal dominant disease.

Castleman's disease is a rare disorder characterised by non-cancerous benign growth that may develop in the lymph node tissue throughout the body.

Sickle-cell disease is a hereditary blood disorder, characterised by red blood cells that assume an abnormal, rigid, sickle shape. Sickling decreases the cells' flexibility and results in a risk of various life-threatening complications. This sickling occurs because of a mutation in the haemoglobin gene.

Mitochondrial neurogastrointestinal encephalopathy syndrome is a rare autosomal recessive mitochondrial disease. Unlike typical mitochondrial diseases caused by mitochondrial DNA (mtDNA) mutations, MNGIE is caused by mutations in the TYMP gene, which encodes the enzyme thymidine phosphorylase.

Only one mutated copy of the gene will be necessary for a person to be affected by an autosomal dominant disorder. Each affected person usually has one affected parent. The chance a child will inherit the mutated gene is 50%. Autosomal dominant conditions  have reduced penetrance, which means although only one mutated copy is needed, not all individuals who inherit that mutation go on to develop the disease.

Turner syndrome 45,X, encompasses several conditions in human females, of which monosomy X (absence of an entire sex chromosome, the Barr body) is most common. It is a chromosomal abnormality in which all or part of one of the sex chromosomes is absent or has other abnormalities.

SLOS Chromosome SLOS is a metabolic disorder caused by a mutation in the DHCR7 (7-dehydrocholesterol reductase) gene on chromosome 11. People who have SLOS are unable to make enough cholesterol to support normal growth and development.