Complex Inheritance Patterns

Simple Dominance

Incomplete Dominance • One allele does

not completely dominate the other

• Get a “blending” effect

• Three phenotypes- the heterozygous genotype has its own phenotype

http://www.emc.maricopa.edu/faculty/farabee/biobk/incomdom.gif

Incomplete Dominance

Codominance

• Both alleles are equally dominant

• Three phenotypes• Two completely different

letters used• Example: AB blood type checkered chickens

roan cattle

http://users.adelphia.net/~lubehawk/BioHELP!/rw01.jpg

Codominance

Multiple Alleles• Genes that have more than two allele

forms within a population (remember that individuals can only have

two alleles)Examples: fur color in rabbits, blood

types in humans

ABO blood type• In human blood

there are 3 different alleles that control blood type

• This results in 4 phenotypes.

A and B are dominant over O

A and B are codominant

http://faculty.ircc.edu/faculty/tfischer/images/blood%20types.jpg

Frequency of blood types(includes Rh factor)

http://images.google.com/imgres?imgurl=http://bloodcenter.stanford.edu/images/bloodtypes.jpg&imgrefurl=http://bloodcenter.stanford.edu/about_blood/blood_types.html&h=249&w=400&sz=32&hl=en&start=6&tbnid=cLwigs-NpY07PM:&tbnh=77&tbnw=124&prev=/images%3Fq%3Dblood%2Btypes%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DG

Polygenic Traits• Many genes

controlling one trait• Most of the traits we

see in humans are this type of pattern

Examples: hair color, skin color, height, etc

• Show a wide range of phenotypes that strengthen in intensity

http://www.svgs.k12.va.us/Courses/MolecularBiology/powerpoints/genetics14_files/slide0093_image056.gif

Sex-linked Inheritance

• Genes that are found on the X chromosome

• Traits carried on the X chromosome are expressed more in males because they only have one X chromosome (XY) compared to females (XX)

• Examples: colorblindness, Hemophilia A, Duchenne muscular dystrophy

Sex-linked inheritance

Colorblindness

• As in other sex-linked traits, the disorder is passed on by mothers to their sons

• Fathers can only pass on the trait to their daughters

How do doctors test for color vision deficiency?

Nature vs. Nurture?

• The environment can play an effect on how genes are expressed

• Climate, soil, and food nutrition can affect growth of an organism

Ex. Hydrangeas are affected by soil pH

Blue-acidicPink-basic

http://images.google.com/imgres?imgurl=http://www.goodgardenbooks.co.uk/GGB/Images/Hydrangeas.jpg&imgrefurl=http://www.goodgardenbooks.co.uk/GGB/HTML/Hydrangeas.html&h=225&w=300&sz=23&hl=en&start=8&tbnid=FipzLSroBC9IwM:&tbnh=87&tbnw=116&prev=/images%3Fq%3Dhydrangeas%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DG

Gene Linkage• Some traits seem to always be together

because they are close together on the same chromosome.

• Known as linked genes or linkage groups

Ex. Red hair and freckleshttp://j-walkblog.com/index.php?/weblog/2006/08/04/