Non mendelian inheritance
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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

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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


Example of incomplete dominance snapdragons

Example of incomplete dominance: Snapdragons


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


Example of codominance color of cornsnakes

Example of codominance:Color of cornsnakes


Cornsnakes

AA

AB

BB

Cornsnakes


Another example of codominance roan cows and horses

Another Example of codominance:Roan Cowsand 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


Types of blood

Anything strange

about this one?

Types of Blood

A

O

B

AB


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)


Acromegaly andr the giant

Acromegaly: André the Giant


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)


Eye color continued

Eye color continued


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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