Medelian Biology

• Mendelian Genetics


  Principles of heredity discovered by Gregor Mendel
• Trait: hair length in cats

  • Long hair is recessive
  • Short hair is dominant
• Trait: eye color

  • E is dominant, e is recessive
  • Father's genotype: Ee, phenotype: black
  • Mother's genotype: ee, phenotype: blue
• Determining genotype and phenotype


  1. E

  2. e

  3. Ee

  4. ee

  
• Homozygous genotype


  Genotype of "HH" or "hh"
• Homozygous dominant


  Genotype of "HH"
• Homozygous recessive


  Genotype of "hh"
• Heterozygous genotype


  Genotype of "Hh"
• Monohybrid cross


  1. H

  2. h

  3. HH

  4. Hh

  5. hh
• Phenotype


  Physical traits of the organism
• It only takes one dominant allele for a dominant trait to show up

  
• Reminders: Genotype vs Phenotype, Homozygous vs Heterozygous

  
• Sample problem 1


  1. B

  2. b

  3. BB

  4. Bb

  5. bb
• Sample problem 2


  1. h

  2. H

  3. Hh

  4. Hh

  5. hh
• Sample problem 4


  1. X

  2. Y

  3. XX

  4. XY

  5. XX

  6. XY
• Sample problem 7
• Sample problem 8
• Gregor Mendel


  The Father of Genetics
• Gregor Mendel discovered the principles of heredity
• Gregor Mendel's experiments on pea plants led to his discoveries
• Dihybrid and two-trait crosses

  More Punnett squares
• Sex chromosomes


  X and Y
• Sex-linked traits


  • Colour blindness
  • Haemophilia
• Incomplete dominance


  Neither allele is completely dominant, resulting in a blended phenotype

  
• Codominance


  Both alleles are expressed equally, resulting in a mixed phenotype
• Multiple alleles


  More than two alleles for a single trait
• Polygenic inheritance


  • Skin colour
  • Height
  • Intelligence
• Epistasis


  One gene masks or interferes with the expression of another gene
• Pleiotropy


  One gene affects multiple phenotypic traits

  
• Pleiotropy


  • Sickle-cell disease
  • Marfan syndrome