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Mendelian Genetics

Mendelian Genetics. AP Biology Unit 3. Mendel’s Experiments. Crossbred Pea Plants P, F1, F2 generations. 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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Mendelian Genetics

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  1. Mendelian Genetics AP Biology Unit 3

  2. Mendel’s Experiments • Crossbred Pea Plants • P, F1, F2 generations

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

  4. 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

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

  6. Law of Segregation • “Two alleles for a trait separate during gamete formation” • Gametes can have different alleles

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

  8. Phenotype Ratios • Characteristic possible phenotype ratios always occur • 2:2 (1:1) • 3:1 • 4:0 (1:0)

  9. 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

  10. 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)

  11. Blood Type Alleles • Codominance = both IA and IB alleles are dominant • Multiple alleles (more than 2 alleles)

  12. Practice Problem #1 • The Huntington’s disease allele is dominant (represented as “H”). • A husband’s genotype is Hh; a wife’s genotype is hh • Which of them will develop Huntington’s disease • What are the possible genotypes for their children? What are the chances their child will have Huntington’s Disease?

  13. Answer • The husband will develop Huntington’s Disease • Children could be Hh (50% chance) or hh (50% chance) • So there is a 50% chance their child will have Huntington’s disease.

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