Mendelian genetics - particulate (instead of blending) theory of inheritance

• inherited characters determined by genes
• genes occur in pairs (from maternal/paternal homologous chromosomes)
• Law of Segregation - only 1 chromosome from each pair found in gametes
• Law of Independent Assortment - genes on different chromosomes distributed randomly into gametes
• gene - unit of heredity on chromosomes
• allele - alternate states of genes, contributed from parents
• dominant alleles - masks expression of other alleles (designated by capital letter)
• recessive alleles - expression masked by dominant alleles (designated by lower-case letter)
• genotype - all alleles present in the cell
• phenotype - physical appearance of a trait
• homozygous - when paired alleles are identical
• heterozygous - when paired alleles are different

types of inheritance

• simple dominance - certain allele completely dominant over another
• incomplete dominance - heterozygous genotype results in mixed characteristic
  • red/white flowers create pink flowers when cross-bred
• lethal inheritance - inherits gene that kills offspring
  • albino seedlings cannot photosynthesize, eventually die
• codominance - evident in blood types
  • 4 blood types - A, B, AB, O; determined by antigens (proteins) on surface of cells
  • A blood - has A antigens, antibodies against B blood cells
  • B blood - has B antigens, antibodies against A blood cells
  • AB blood - has A/B antigens, no antibodies
  • O blood - has antibodies against A/B blood, no antigens

human traits - many determined by just single gene

• widow's peak - pointed hairline dominant over straight hairline
• bent little finger - little finger bends toward 4th finger (dominant)
• albinism - lack pigment in skin (recessive)
• pigmented iris - pigments (dominant) hides blue/gray color of iris back layer
• attached earlobes - free earlobes dominant over attached earlobes
• hitchhiker's thumb - last joint of thumb bends back over 60 degrees (recessive)
• interlacing fingers - crossing left thumb over right dominant over crossing right over left
• PTC tasting - ability to taste bitterness dominant over inability
• mid-digital hair - hair on middle segment of fingers (dominant)

human diseases -

• cystic fibrosis - chronic bronchial obstruction, growth reduction
• galactosemia - can't metabolize galactose in human milk (autosomal recessive)
• phenylketonuria (PKU) - inability to metabolize phenylalanine, leads to mental retardation
• Huntington's disease - uncontrollable, involuntary muscle movements
• occurs late in life, often gets passed on to offspring
• juvenile retinoblastoma - cancer of retina

transposons - fragments of DNA that can move in chromosome

• useful in genetic engineering
• can insert foreign DNA into chromosome