Mendelian Genetics

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Mendelian Genetics
AP Biology Unit 3
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Mendels Experiments

• Crossbred Pea Plants
• P, F1, F2 generations

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Alleles

• Alleles are different (alternate) forms of a gene
• How do alleles relate to homologous chromosomes?
• Homologous chromosomes may contain different
  alleles

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Yeast Complementation Alleles

• How did alleles play a role in the yeast
  complementation experiment?
• Strains of yeast have different alleles
• When mated, the a normal allele could complement
  a mutated allele
• HA1 mutated ade 1 allele , normal trp allele
• HBT normal ade1 allele, mutated trp allele

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Dominant vs. Recessive Alleles

• Dominant Allele
• Determine phenotype if there is a copy present
• Recessive Allele
• Need 2 copies to determine phenotype

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Law of Segregation

• Two alleles for a trait separate during gamete
  formation
• Gametes can have different alleles

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Punnett Squares

• Allow you to predict possible genotypes of
  offspring if parental genotypes are known
• Phenotypes can be deduced from the genotypes

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Phenotype Ratios

• Characteristic possible phenotype ratios always
  occur
• 22 (11)
• 31
• 40 (10)

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Test Cross

• Suppose you have an organism with a dominant
  phenotype
• You want to determine its genotype PP or Pp?
• Cross with a recessive phenotype to determine
  genotype test cross

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Law of Independent Assortment

• Pairs of alleles for a given trait segregate
  independently of other pairs of alleles for
  another trait
• Ex. YyRr can result in YR, Yr, yR, or yr
• This only applies to two traits on different
  chromosomes (NOT LINKED)

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Blood Type Alleles

• Codominance both IA and IB alleles are dominant
  
• Multiple alleles (more than 2 alleles)

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Practice Problem 1

• The Huntingtons disease allele is dominant
  (represented as H).
• A husbands genotype is Hh a wifes genotype is
  hh
• Which of them will develop Huntingtons disease
• What are the possible genotypes for their
  children? What are the chances their child will
  have Huntingtons Disease?

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Answer

• The husband will develop Huntingtons Disease
• Children could be Hh (50 chance) or hh (50
  chance)
• So there is a 50 chance their child will have
  Huntingtons disease.