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Genetic Inheritance and Alleles: Exploring Mendelian Ratios and Gene Interactions

Understand Mendelian principles, multiple alleles, and gene interactions with examples in Drosophila and mice. Learn about codominance, lethal alleles, and novel phenotypes.

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Genetic Inheritance and Alleles: Exploring Mendelian Ratios and Gene Interactions

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  1. Chapter 4: Modification of Mendelian Ratios Allele *Wild-type allele *Mutant allele Conventional symbols for alleles: recessive allele- initial letter of the name of the recessive trait, lowercased and italicized dominant allele- same letter in uppercase Genetic nomenclature is extremely diverse!

  2. Cross between parents with contrasting traits:Red flowersor white flowers Offspring with an intermediate phenotype: pink flowers Incomplete or Partial Dominance

  3. Codominance: Example: MN Blood group- red blood cells contain a transmembrane glycoprotein (glycophorin); two different forms of this protein exist, M and N

  4. Multiple Alleles: Examples: *Table 4.1: over 100 alleles at a given locus in Drosophila *ABO Blood group in humans *Characterized by the presence of glycoprotein antigens on the surface of red blood cells *Distinct from the M and N antigens *Also exhibits codomiance

  5. Lethal Alleles: Example: Coat color in mice *A = agouti = wild-type allele *AY = yellow = mutant allele

  6. Combining modified modes of inheritance:

  7. Gene interaction: *Epistasis Example: *In Drosophila, the recessive gene eyeless (when homozygous) prevents the expression of eye color genes present in genome *Coat color in mice *Black (B) is dominant to brown (b) *Second gene responsible for allowing pigment to be deposited in hair C = presence, c = absence (colorless)

  8. *Novel phenotypes due to gene interaction Example: disc-shaped fruit (AABB) X long fruit (aabb) pepper color

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