Genetics and Inheritance

Tay-Sachs Disease

• Genetics:
  • 'T' denotes a normal gene; 't' indicates Tay-Sachs disease.
  • Involves the loss of a lysosomal enzyme in the brain.
  • Lipid accumulation causes blindness, dementia, seizures, and death before age three.
• Inheritance Patterns:
  • Two genes govern each trait: can be homozygous dominant (TT), heterozygous (Tt), or homozygous recessive (tt).
  • Disease typically results from two carrier parents (Tt x Tt).
  • Genotype ratio: 1 normal (TT): 2 carriers (Tt): 1 diseased (tt).
  • Phenotype ratio: 3 normal (includes carriers) to 1 diseased.
  • Children from two heterozygous parents have a 25% chance of disease, 50% chance of being a carrier, and a 25% chance of being normal.

Dominant Diseases

• Example: Huntington's Disease
  • 'H' indicates disease, 'h' is normal.
  • Having one diseased parent gives each child a 50% chance of having the disease.
  • With two diseased parents, the chance increases to 75%.

X-linked Diseases

• Characteristics:
  • Carried on the X chromosome.
  • Include red-green color blindness, Duchenne's muscular dystrophy, hemophilia.
• Inheritance:
  • Females are carriers, males express the disease.
  • A carrier female with a non-diseased male: 50% chance daughters are carriers, 50% chance sons have the disease.

Blood Types and Codominance

• Blood Type Genetics:
  • Types: A, B, AB, O
  • 'IA' and 'IB' are dominant; 'i' is recessive.
• Codominance:
  • Type A: IAIA or IAi
  • Type B: IBIB or IBi
  • Type AB: IAIB
  • Type O: ii
• Inheritance Patterns:
  • Both parents must be heterozygous (e.g., A and B with recessive i) for a child to be type O.

Multifactorial Traits

• Examples: Skin color and height.
• Characteristics:
  • Multiple genes involved.
  • Environmental factors, like nutrition, also play a role.
  • Parents can pass on a range of genetic combinations affecting traits like height.