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Non-Mendelian Inheritence

Non-Mendelian Inheritence . Most patterns of inheritance are more complex than those that Mendel identified. Other patterns include incomplete dominance, codominance, multiple alleles, and polygenic inheritance.

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Non-Mendelian Inheritence

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  1. Non-Mendelian Inheritence • Most patterns of inheritance are more complex than those that Mendel identified. • Other patterns include incomplete dominance, codominance, multiple alleles, and polygenic inheritance. • Incomplete dominance occurs when two alleles influence the phenotype and results in a phenotype intermediate between the dominant trait and the recessive trait. • Example: carnations and snapdragons

  2. P Generation Red White RR WW R W Gametes

  3. P Generation Red White R W Gametes Pink F1 Generation RW R W Gametes

  4. P Generation Red White RR WW R W Gametes Pink F1 Generation RW R W Gametes Sperm R W F2 Generation R CRCW CRCR Eggs W CRCW CWCW

  5. Codominance • Codominance occurs when both alleles for a gene are expressed in a heterozygous offspring. • In Codominance, the "recessive" & "dominant" traits appear together in the phenotype of hybrid organisms. red x white ---> red & white spotted • Example: In cows if you cross a pure bred red cow with a pure bred white cow, the offspring are roan

  6. Multiple Alleles • Genes that have more than two alleles for a trait. • Each individual can only have two, but in the population more than two exist. • Example: ABO blood types • An enzyme encoded by the IA allele adds one type of sugar called “A”, whereas the enzyme encoded by the IB allele adds a different type of sugar “B”; the enzyme encoded by the i allele adds neither • Humans have three alleles for blood type • IA: Type A • IB: Type B • I: Type O • A and B are both dominant over O, but are codominant with each other

  7. Carbohydrate Allele Phenotype (blood group) Red blood cell appearance Genotype IA A B IB i none (a) The three alleles for the ABO blood groups and their associated carbohydrates IAIA or IA i A B IBIB or IB i AB IAIB ii O (b) Blood group genotypes and phenotypes

  8. Polygenic Inheritance • A character that is influenced or affected by more than one gene is called a polygenic character. • Eye color, height, and skin color are examples of polygenic characters. Most characters are polygenic.

  9. AaBbCc AaBbCc Sperm Eggs Phenotypes: 1/64 6/64 15/64 20/64 15/64 1/64 6/64 Number of dark-skin alleles: 2 6 0 3 4 5 1

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