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Non Mendelian Inheritance

Non Mendelian Inheritance. Exceptions to the rules. Observation?. Sometimes the heterozygous offspring have a trait that isn’t exactly the trait of either purebred parent. Incomplete Dominance. Hybrid (heterozygote) is a “blend” of two parent phenotypes Dominant allele isn’t completely so….

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Non Mendelian Inheritance

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  1. Non Mendelian Inheritance Exceptions to the rules

  2. Observation? • Sometimes the heterozygous offspring have a trait that isn’t exactly the trait of either purebred parent

  3. Incomplete Dominance • Hybrid (heterozygote) is a “blend” of two parent phenotypes • Dominant allele isn’t completely so…

  4. Incompl. Dom Symbols • AA (red) x aa (white) 100 % Pink

  5. Example of incomplete dominance: Snapdragons

  6. Codominance • No recessive allele • Both "dominant" traits appear together in the phenotype of hybrid organisms.

  7. Codominance Symbols • AA = Dominant 1 • BB = Dominant 2 • AB = Dominant 1 & Dominant 2

  8. Example of codominance:Color of cornsnakes

  9. AA AB BB Cornsnakes

  10. Another Example of codominance:Roan Cows and Horses • Red x White  Red and White Spotted

  11. Multiple Alleles • More than 2 alleles affect the phenotype equally & separately • not blended phenotype • human ABO blood groups • 3 alleles • IA, IB, i • IA & IB alleles are co-dominant • i allele recessive to both

  12. Example of multiple alleles: Human Blood Type • Alleles: • IA=A allele • IB=B allele • i=O allele

  13. Anything strange about this one? Types of Blood A O B AB

  14. Pleiotropy • Most genes are pleiotropic • one gene affects more than one phenotypic character • 1 gene affects more than 1 trait • dwarfism (achondroplasia) • gigantism (acromegaly)

  15. Acromegaly: André the Giant

  16. Inheritance pattern of Achondroplasia Aa x aa Aa x Aa dominantinheritance a a A a  Aa Aa AA Aa A A dwarf dwarf lethal a a aa aa Aa aa 50% dwarf:50% normal or1:1 67% dwarf:33%normalor2:1

  17. Epistasis • One gene completely masks another gene • coat color in mice = 2 separate genes • C,c:pigment (C) or no pigment (c) • B,b:more pigment (black=B) or less (brown=b) • cc = albino, no matter B allele • 9:3:3:1 becomes 9:3:4 B_C_ B_C_ bbC_ bbC_ _ _cc _ _cc

  18. Epistasis in Labrador retrievers • 2 genes: (E,e) & (B,b) • pigment (E) or no pigment (e) • pigment concentration: black (B) to brown(b) eebb eeB– E–bb E–B–

  19. Polygenic Trait • More than 1 gene controls the trait • Each gene may be inherited separately

  20. Symbols of Polygenic Inheritance • A, a = gene 1 • B, b = gene 2 • Etc…

  21. Polygenic inheritance • Some phenotypes determined by additive effects of 2 or more genes on a single character • phenotypes on a continuum • human traits • skin color • height • weight • intelligence • behaviors

  22. Example of a polygenic trait • Eye color • There are genes for • Tone of pigment (what color it is) • The amount of pigment • Position of pigments (look at people’s eyes- there are many different patterns in the iris)

  23. Eye color continued

  24. Sex-linked inheritance • Alleles carried on sex chromosomes • Gender influences phenotype

  25. Symbols of Sex-linked inheritance • XH = dominant allele • Xh = recessive allele • Y = no allele for this trait

  26. Examples: • Hemophilia • Red-green color-blindedness • Male pattern baldness

  27. X-inactivation… • If a male is XY, female is XX, how can females get “double” the amount of “X” chromosome DNA? • The answer? The second “X” is turned off in females • = “Dosage compensation” or “X inactivation”

  28. Environmental Influences • Diet, exercise, stress… • Sunlight, water alter phenotypes in plants • Even temperature affects coloration on Siamese cats!

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