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INCOMPLETE DOMINANCE
• Pattern of gene expression in which the phenotype of a heterozygous individual is intermediate between those of homozygous parents.
• Cases in which one allele is not completely dominant over another.
• Snapdragons
http://faculty.pnc.edu/pwilkin/incompdominance.jpg
http://www.dobermann-review.com/info/genetics/mendels_genetic_laws/Gregor%20Mendel.jpg
HUH?
http://2.bp.blogspot.com/_uPFMFfHgGGg/SygBEtl5D1I/AAAAAAAAAKc/nylZiiL2k7s/s320/incomplete+dominance.jpg
CODOMINANCE
• The condition in which both alleles in a heterozygous organism are expressed.
• BOTH alleles contribute to the phenotype.
• The two alleles don’t blend, but are rather both present in the offspring.
• Examples: Roan animals, Speckled animals, etc…
http://search.vadlo.com/b/q?rel=2&keys=Dominance+Incomplete+Dominance+Codominance+PPT
Roan Horse
Roan Cattle
Variegated Clover
http://3.bp.blogspot.com/_zUPrgMM5tUg/SSVdrs59_uI/AAAAAAAAAA8/qJGjG2nZPhk/s200/codominance.GIF
http://www.ccs.k12.in.us/chsteachers/BYost/Biology%20Notes/CH11notescoincompletedom_files/image004.jpg
MULTIPLE ALLELISM
• When there is more than 2 alleles possible for a given gene.
• Allows for a larger number of genetic and phenotypic possibilities.
Multifactorial
• Referring to control of the expression of a trait by several genes and environmental factors.
• Many multifactorial traits show continuous distribution.
Multifactorial
• E.g. Human height usually between 120cm and 200cm, however these genes cannot be fully expressed without all the necessary nutrients from a healthy diet
http://www.babble.com/CS/blogs/droolicious/menace-height.jpg
Sex-linked Traits• Traits (genes) located on the
sex chromosomes
• Sex chromosomes are X and Y–XX genotype for females–XY genotype for males
• Many sex-linked traits carried on X chromosome
Sex-linked Traits
Sex Chromosomes
XX chromosome - female Xy chromosome - male
Color-blindness
Example: Colorblindness
Consequences
• This leads males to be more vulnerable to diseases that are the result of defective genes on the X chromosome
• Females can be “carriers-” Have a single allele for a trait, but does not actually have the trait (heterozygous)
2. In a certain breed of cow the gene for red fur, R, is codominant with that of white fur, W. What would be the phenotypic & genotypic ratios of the offspring if you breed a red cow and a white bull? What would they be if you breed a red & white cow with a red & white bull?
3. A rooster with grey feathers is mated with a hen of the same phenotype. Among their offspring 15 chicks are grey, 6 are black and 8 are white.
a. What is the simplest explanation for the inheritance of these colors in chickens?
b. What offspring would you expect from the mating of a grey rooster and a black hen?
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