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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

Non Mendelian Inheritance

Exceptions to the rules

observation
Observation?
  • Sometimes the heterozygous offspring have a trait that isn’t exactly the trait of either purebred parent
incomplete dominance
Incomplete Dominance
  • Hybrid (heterozygote) is a “blend” of two parent phenotypes
  • Dominant allele isn’t completely so…
incompl dom symbols
Incompl. Dom Symbols
  • AA (red) x aa (white)

100 % Pink

codominance
Codominance
  • No recessive allele
  • Both "dominant" traits appear together in the phenotype of hybrid organisms.
codominance symbols
Codominance Symbols
  • AA = Dominant 1
  • BB = Dominant 2
  • AB = Dominant 1 & Dominant 2
another example of codominance roan cows and horses
Another Example of codominance:Roan Cows and Horses
  • Red x White  Red and White Spotted
multiple alleles
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
example of multiple alleles human blood type
Example of multiple alleles: Human Blood Type
  • Alleles:
    • IA=A allele
    • IB=B allele
    • i=O allele
pleiotropy
Pleiotropy
  • Most genes are pleiotropic
    • one gene affects more than one phenotypic character
      • 1 gene affects more than 1 trait
      • dwarfism (achondroplasia)
      • gigantism (acromegaly)
inheritance pattern of achondroplasia
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

epistasis
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

epistasis in labrador retrievers
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–

polygenic trait
Polygenic Trait
  • More than 1 gene controls the trait
  • Each gene may be inherited separately
symbols of polygenic inheritance
Symbols of Polygenic Inheritance
  • A, a = gene 1
  • B, b = gene 2
  • Etc…
polygenic inheritance
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
example of a polygenic trait
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)
sex linked inheritance
Sex-linked inheritance
  • Alleles carried on sex chromosomes
  • Gender influences phenotype
symbols of sex linked inheritance
Symbols of Sex-linked inheritance
  • XH = dominant allele
  • Xh = recessive allele
  • Y = no allele for this trait
examples
Examples:
  • Hemophilia
  • Red-green color-blindedness
  • Male pattern baldness
x inactivation
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”
environmental influences
Environmental Influences
  • Diet, exercise, stress…
  • Sunlight, water alter phenotypes in plants
  • Even temperature affects coloration on Siamese cats!
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