beyond mendel l.
Skip this Video
Loading SlideShow in 5 Seconds..
Beyond Mendel PowerPoint Presentation
Download Presentation
Beyond Mendel

Loading in 2 Seconds...

play fullscreen
1 / 24

Beyond Mendel - PowerPoint PPT Presentation

  • Uploaded on

Most common,

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about 'Beyond Mendel' - Kelvin_Ajay

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
beyond mendel

Beyond Mendel

Not simply “dominant & recessive”

multiple allelic traits
Multiple allelic traits
  • Can occur in two ways:
    • New alleles arise by mutation
    • Genes may have more than 2 allele types
new alleles by mutation
New alleles by mutation
  • mutations: rare, stable, & inherited changes in DNA
    • Most common, “expected” allele is defined as the wildtype
    • Other alleles are defined as mutant alleles
      • Ex. Eye color in fruit flys: red eyes  wildtype vs. white eyes  mutant
new alleles by mutation4
New alleles by mutation
  • polymorphic allele: genetic locus with a wild-type that occurs < 99% of the time
genes with multiple alleles
Genes with multiple alleles
  • Occur from random mutation
  • More than 2 allele types exist for the gene, although each individual contains only 2 alleles for the gene (one from mom & one from dad)
  • Increase the number of phenotypes (not just Mendel’s two types)
genes with multiple alleles6
Genes with multiple alleles
  • Example:

coat color in rabbits

one gene with 4 alleles with a dominant heirarchy:


C (dark gray) ch (chinchilla)

h (himalayan) c (albino)

no dominant over recessive
No dominant over recessive
  • incomplete dominance: one allele is not dominant over another
    • heterozygotes: show interimediates between 2 allele types
  • codominance: one or more alleles are dominant &
    • heterozygotes: both alleles get expressed in the phenotype
incomplete dominance
Incomplete dominance
  • Ex. Snapdragons


white x red

incomplete dominance11
Incomplete dominance
  • Follows Mendel’s laws because in F2 generation, all 3 phenotypes appear (no blending)
  • Instead of expected 3:1 ratio in F2 generation, get 1:2:1 ratio of offspring
  • Two alleles at a locus produce two different phenotypes that are both expressed in the heterozygote
  • Ex. Blood types
    • Four phenotypes possible:

A, B, AB, and O

    • 3 possible alleles:

IA, IB, iO

pleiotropic alleles
Pleiotropic alleles
  • single allele can affect more than one phenotype

Ex. Allele responsible for coloration pattern in Siamese cats

( light body, darker extremeties)

Same allele is responsible for the crossed eyes of the cats

pleiotropic alleles16
Pleiotropic alleles
  • Allele results in the same protein, but affects two different characteristics
genes effecting genes
Genes effecting genes
  • epistasis: the phenotypic expression of one gene is affected by another gene

Ex. Coat color in mice

- wild-type (B): agouti (grayish pattern resulting from bands on the individual hairs)

bb: no bands  black

epistasis in mice
Epistasis in mice
  • A second locus on another chromosome affects early development of hair pigmentation

A (normal pigmentation)

aa (no pigmentation)

epistasis in mice19
Epistasis in mice
  • All mice having aa are albino, regardless of the genotype at the B locus
  • When considering both loci together in a cross, don’t get the expected Mendelian ratio in the F2 generation (9:3:3:1)
epistasis in mice20
Epistasis in mice

AABB x aabb


AaBb x AaBb

9 agouti: 3 black: 4 albino

effect of environment
Effect of environment
  • Genotype and environment interact to determine the phenotype of an organism.
    • Light, temp., nutrition
effect of environment22
Effect of environment
  • Consider 2 parameters:
    • Penetrance: proportion of individuals in a group with a given genotype that show the expected phenotype
    • Expressivity: degree to which a genotype is espressed in an individual
environment genotype
Environment & genotype
  • Result in a population with a continuous variation (instead of two extremes)
    • due to multiple genes, each with multiple alleles, and environmental influences