Genetic

Disease

Genetic DiseaseDominant Inheritance•rarely passed on as people with the disease don’t reproduce•exception: Huntington’s Disease

-symptoms appear 40 years + (too late to stop reproduction)-occasionally involuntary flailing movements of arms and legs-eventual dementia (loss of ability to think clearly)

Genetic DiseasesDominant gene Disorder Description

Achondroplasia (form of dwarfism)

- can be inherited or as a mutation

- short limbs, prominent head, normal intelligence

Facioscapulohumeral muscular dystrophy

- muscular dystrophy in the face (difficult to close eyes and constant pouting lips)

Neurofibromatosis - Tumours along peripheral nerves

Genetic DiseaseRecessive Inheritance e.g Albinism• melanin: yellow black pigment (made from an amino acid,

tyrosine)• Produced by melanocytes (special skin cells)• Albinism: one of the enzymes which helps form tyrosine is

missing no melanin is formed• Dominant allele: normal enzyme production• Recessive allele: abnormal, no enzyme produced no

tyrosine no melanin• Amount of melanin produced depends on many other

alleles

Genetic DiseasesRecessive gene

DisorderDescription

Thalassaemia- Defect in haemoglobin

formation (anaemia)

Phenylketonuria (PKU)

- Defect in phenylalanine hydroxylase (enzyme) which converts phenylalanine into tyrosine. If not present, phenylalanine builds up in blood (toxic), results in extreme mental retardation & tendency to epilepsy

Cystic Fibrosis

- Chest infections, lack of digestive enzymes and increased salt loss. Special diet can reduce symptoms

Genetic DiseasesGenetic Counselling• Advice given regarding risks of genetic abnormalities in a

child• may result in a termination Human Genome Project• Genome: complete set of genetic info of an organism.

(mapping sequence of nucleotides in all genes (20000-25000) in all 46 chromosomes)

• launched in 1990 – 2003• all genes have been identified in addition to most of the

possible alleles for each gene.• genetic counsellors are able to make predictions from an

individuals genome as to the likeliness of a certain disease expressing itself within the individuals lifetime.