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Human Genetic Disorders
Two Types:
Autosomal Recessive Disorder – Most common type, only shows in the
phenotype when genotype is homozygous recessive
Autosomal Dominant Disorder – These condition will appear in the
phenotype when the genotype is heterozygous and homozygous
recessive
Polygenic Disorders – caused by multiple genes common examples are
hypertension, diabetes, allergies, cleft lips, schizophrenia
Pleiotropy – genes affect more than one characteristic can have physical
and mental problems
Autosomal Recessive Disorders
1. Tay-Sachs – Chromosome 15 – Affects people of Jewish and
Mediterranean descent. Lack of an enzyme causes a build-up of lipids
in the lysosomes of brain cells. Death by age 3 or 4 years.
2. Cystic Fibrosis – Chromosome 7 – causes salty sweat and thick
mucus in the lungs also affects the pancreatic duct so causes
digestive problems. May live to 35 years
3. Phenylketonuria – Chromosome 12 – (Black urine disease) Missing an
enzyme to metabolize phenylalanine an amino acid. This cause
problems with brain development during first seven years if not
controlled. Cannot digest artificial sweetener Nutrasweet.
4. Sickle Cell Anemia –Chromosome 11 – Red blood cells collapse in low
oxygen level taking on a sickle shape. Leads to anemia, weakness,
fever, spleen damage, kidney failure due to clots. Heteozygous
condition will give immunity to malaria.
Autosomal Dominant Disorders – Usually passed on to children
before symptoms start in parents
1. Neurofibromatosis – Chromosome 17 - (called Von Recklinghausen)
develop large brown spots on skin that develop into tumors and
cancer.
2. Huntington's Disease – Chromosome 4 – Appear normal until middle
age 30-35 years then a progressive degeneration of brain tissue
develops until death in 10 to 15 years.
3. Achrondroplasia – Chromosome 4 – Dwarfism only affects long bone
development AA lethal, Aa dwarf, aa no problems
Multiple Alleles – Many genes competing for two loci on the
chromosomes. The result may be codominance
Example : Blood Types
A = Ia Ia or Iai
B = IbIb or Ibi
AB = IaIb (codominant condition)
O = ii
Rh factors – Named after Rhesus Monkeys – Seven factors these
are proteins on the surface of the RBCs – If you have 1 or more
factors you are + no factors you are -