Biology 205 Extensions of Mendelian Genetics

Chapter 4

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1. Multiple alleles

• Define what is meant by multiple alleles
• Discuss and solve multiple allele inheritance problems
• ABO blood system, Drosophila eye color.

2. Gene interactions and modified genetic ratios

• Discuss and solve problems related to general gene interactions e.g. comb shape in chickens
• Define epistasis and be able to solve problems concerning epistasis.
• Explain how epistasis can arise from a metabolic point of view.
• Discuss and solve problems related to epistasis:
• Coat color in rodents
• Flower color in sweet peas - explain how the 9 - 7 ratio comes about for the F2's. See figures 4.7 and 4.8

4. Essential genes and lethal alleles

• Define essential gene and lethal allele
• Solve problems related to lethal alleles
• Yellow body color in mice. See p 87
• Tay-sacs. See p 87- Tay sacs is a recessive lethal
• Hemophilia - X linked lethal at least when not treated!
• Note that the yellow coat color allele in rodents is an example of an allele that is dominant with respect to coat color but it is a recessive lethal.

5. Gene expression and environmental effects

• Distinguish between penetrance and expressivity p 88
• Penetrance - for a certain dominant or recessvie gene - frequency of the gene's expression in individuals having that allele
  • example for individuals who are Aa, if the dominant allele is expressed 100% of the time, it has complete penetrance. If the dominant allele is expressed 80% of the time it has only 80% penetrance
• Expressivity refers to a situation where individuals of a known genotype express a range of phenotypes.
• Distinguish between sex linked traits, sex limited traits and sex influenced traits
• Give examples of the effects of the following on gene expression:
• Temperature - expression of an allele may be temperature sensitive:

  Melanin deposition in fur of Siamese cat. p 90

  There are also temperature sensitive polymerases in bacteria

• Chemicals - example in text is PKU
• Define norm of reaction
  • - range of phenotypes a particular genotype can produce
  • -give examples of a single genotypes producing multiple phenotypes

pgd Created 09/15/03 revised 02/13/05

Problems page 95-98:

4.1, 4.4, 4.5, 4.7, 4.14, 4.15, 4.16, 4,21, 4.26(See 4.25 for details first), 4.30. (See 4.29 first)