Alternate Patterns of

Inheritance

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.

Environmental FactorsEnvironmental factors – soil pH affects the color of hydrangea flowers

Acidic soil makes the flowers blue, basic or alkaline soil makes the flowers pink

Environmental factors– temperature and season affect the

coat color of arctic foxes

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)

Sex – Linked Traits• Example- Hemophilia

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?