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Genetics

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
Subject: 
Biology
Subject X2: 
Biology

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