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Patterns of Intermediate Inheritance

Patterns of Intermediate Inheritance. Exceptions to Mendel’s Principles. Mendel’s 3 principles provide us with an important foundation in building our knowledge of genetics. However, there are many types of inheritance patterns that do not follow the principle of dominance.

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Patterns of Intermediate Inheritance

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  1. Patterns of Intermediate Inheritance

  2. Exceptions to Mendel’s Principles • Mendel’s 3 principles provide us with an important foundation in building our knowledge of genetics. • However, there are many types of inheritance patterns that do not follow the principle of dominance.

  3. There are several types of intermediate inheritance patterns: • Co-dominance • Multiple Alleles • Incomplete Dominance • Polygenic Traits • Multifactorial Inheritance

  4. Co-dominance • A trait for which both alleles contribute equally to the phenotype. • Example: Coat color in cows and horses • When a homozygous red cow is crossed with a homozygous white cow they produce a heterozygous cow that is red and white (roan).

  5. Genotype: RR

  6. Genotype: WW

  7. Genotype: RW

  8. Practice Cross - Codominance • A horse that is roan is a blend of red and white colors that result when a red horse is crossed with a white horse. Red (R) horses breed true; and white (W) horses breed true. • What is the genotype of a red horse? • RR • What is the genotype of a white horse? • WW • What is the genotype of a roan horse? • RW

  9. Show the cross between two roan horses (use R and W). • What is the probability that two roan horses will have at least one roan offspring? • 50% • What is the probability that two roan horses will have a white offspring? • 25% R W RR RW R WW W RW

  10. Multiple Alleles • When a gene has more than two possible alleles. • ONLY TWO alleles are inherited. • Example: Rabbit Coat Color is controlled by 4 alleles - C, cch, ch, and c

  11. wild type color CC, Ccch, Cch, Cc

  12. chinchilla color cchcch, cchch, cchc

  13. Himalayan color chc or chch

  14. albino cc

  15. Practice cross: Multiple Alleles • Practice cross: In rabbits there are four different color alleles: • C is dominant over all C = wild type color • cch is dominant to ch & c cch = chinchilla color • ch is dominant to c ch = Himalayan color • C is recessive to all c = albino • Each rabbit can inherit only two alleles. A wild colored rabbit is crossed with an albino and in the offspring there is a Himalayan rabbit.

  16. Show the cross between a wild type and albino rabbit that has a Himalayan baby. • What are the genotypes of the parents? • Parent one : cc • Parent two : Cch • What is the probability that they will have an offspring that is Himalayan? • 50% • What is the probability that they will have an offspring that is albino? • 0% • What is the probability that they will have an offspring that is wild colored? • 50% C ch Cc c ch c c ch c Cc Mult. Alleles & Co-dominance

  17. Incomplete Dominance • Results in a heterozygous phenotype that is a blend of the two homozygous phenotypes. • Examples: mirabilis (four o’clock) plants, coat color in horses • When a homozygous chestnut horse is crossed with a homozygous white horse, they produce a heterozygous tan (palomino) horse.

  18. Genotype: cc (Chestnut)

  19. Genotype: ww

  20. Genotype: cw (Palomino)

  21. Practice Cross – Incomplete Dominance • In Four O’Clocks, the gene for red flowers (r) is incompletely dominant to the gene for white flowers (w). • The heterozygous condition results in pink flowers. • Red Plant Genotype? • rr • White Plant Genotype? • ww

  22. Show the results of a cross between a red Four O’Clock and a white Four O’Clock. • Are the F1 flowers purebred or hybrid? • hybrid • What is the phenotype of the F1 flowers? • pink r r rw rw w rw w rw

  23. Snapdragons Mirabilis plants

  24. Humans & Plants Polygenic • A trait that is controlled by the interaction between 2 or more genes. • Examples: skin color, eye color, height, hair color • Results in a continuum of expressed phenotypes.

  25. Multifactorial Inheritance • The phenotype is a result of an interaction between your genotype and certain environmental factors. • The expression of most all genes is influenced by environmental conditions. • Examples: • Diabetes • Height • Heart Disease • Can inherit a predisposition to all of these diseases/characteristics. • Their development (phenotype) is influenced by environmental factors such as proper nutrition, exercise, quality medical care, etc. Enviro Factors

  26. Examples in plants: • In many plants, the presence of light triggers the production of chloroplasts. • Chemicals that stimulate germination are only produced in the presence of certain temperatures. http://www.dkimages.com/discover/previews/874/30020399.JPG Review of Terms

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