Non-Mendelian

• Does not conform with Mendel's experiment
• This does not diminish the utility of Mendelian genetics since the basic principles of segregation and independent assortment will still be applied here (more complex patterns of inheritance)
• Degrees of Dominance


  Alleles are not completely dominant or recessive
• Multiple Alleles


  Gene has more than two alleles
• Pleiotropy


  A gene produces multiple phenotypes
• Complete Dominance


  Dominant trait manifests upon the organism
• Incomplete Dominance


  Phenotype of the offspring is intermediate trait of the parental varieties, neither allele is dominant over the other
• Incomplete Dominance


  • Red Snapdragons x White Snapdragons = Pink Snapdragons
• Codominance


  Two different alleles are expressed simultaneously, offspring expresses both features of the parents which is phenotypically distinguishable
• Codominance


  • Red (petal) flower x White Flower = Red and White (petal) flower
• An allele is called dominant because it is SEEN in the phenotype, not because it subdues a recessive allele
• Dominance and recessiveness come into play in the pathway from genotype to phenotype
• Tay-Sachs Disease


  Inherited disorder in humans, brain cells of those who suffer this disease cannot metabolize certain lipids because a crucial enzyme does not work properly
• At the organismal level: Alleles of Tay-Sachs qualify as RECESSIVE


  At the biochemical level: Intermediate phenotype is qualified as INCOMPLETE DOMINANCE
• Dominant alleles are not necessarily more common in a population
• Polydactyly


  • Caused by a dominant allele yet only 1 baby out of 400 (in U.S.A) is born with this condition
• Multiple Alleles


  Three or more alleles of the same gene are present in a population
• Multiple Alleles


  • ABO Blood Group
• Pleiotropy


  Genes that have multiple phenotypic effects, affects more than one phenotypic character
• Pleiotropy


  • Multiple symptoms of certain hereditary diseases (cystic fibrosis, sickle-cell disease) are due to pleiotropic alleles
• Epistasis


  One gene affects the phenotype of another due to interaction of their gene products, expression of a gene at one locus alters the phenotypic expression of a gene at a second locus
• Polygenic Inheritance


  More than 1 gene controls the character, quantitative characters: vary in the population in gradations along a continuum, quantitative variation indicates polygenic inheritance, an additive effect of two or more genes on a single phenotype
• Polygenic Inheritance


  • Height, skin color, hair color
• Environmental factors have influence or impact on the phenotype
• The phenotypic range is broadest for polygenic characters, and the environment contributes to the quantitative nature of these characters (e.g. variation of skin color)
• Multifactorial


  Phenotype depends on multiple genes combined with environmental influences