Non-Mendelian Inheritance

Not all traits exhibit simple dominant and recessive expression. Incomplete Dominance Multiple Alleles Codominance Polygenic Traits Environmental Effects

Incomplete Dominance Incomplete dominance – heterozygous phenotype is intermediate between that of either homozygote Produces a blended phenotype

Incomplete Dominance A man with straight hair mates with a woman that has curly hair what is the chance of their offspring having wavy hair? Dad HH Mom hh x H H HH Straight h Hh Hh Hh Wavy h Hh Hh hh Curly 100% Wavy

Codominance Codominance - both alleles are expressed at the same time in the heterozygote Ex: Rhone horse Has both black and white hairs

Example: Problem You breed a white chicken with an Andalusian blue rooster (black and white feathers). What are the potential offspring? Dad BW Mom WW x B W BB Black W BW WW BW Andalusian W BW WW WW White 50% Andelusian; 50% White

Multiple Alleles More than 2 alleles control trait. Diploid organism can only have 2 alleles. Example: Rabbit fur color C (wildtype), ch (himalayan), cch (chinchilla), c (albino) http://pantransit.reptiles.org/images/1998-02-07/ wildtype http://www.catsandrabbitsandmore.com/home himalayan http://didiermervilde.bestofbreeds.net/caviaandrabbits.html chinchilla http://biomesblog.typepad.com/the_biomes_blog/2004/06/ albino

Multiple Alleles Human Blood Type 3 alleles -- IA , IB , and IO IA and IB are codominant IO is recessive Type A blood can be IAIA or IAIO Type B blood can be IBIB or IBIO Type AB blood is IAIB - codominant state Type O blood is IOIO

Blood type A woman with AB blood type has a baby with B blood type. Is it possible for a man with type A blood to be the father? If so what is the mans genotype? Dad IA - Mom IAIB x Type A blood can be IAIA or IAIO Type B blood can be IBIB or IBIO Type AB blood is IAIB - codominant state Type O blood is IOIO IA - IA IAIA IA- IB IAIB IB- Yes Dad must be IAIO

Polygenic Inheritance Wide range (continuum) of phenotypes Human skin color Height and weight Two or more genes responsible for trait.

Polygenic Inheritance Skin Color

Environmental effects Color resembles snowy background in winter The expression of some genes is influenced by environmental factors, such as temperature Some alleles are heat-sensitive Arctic foxes, cats, rabbits make fur pigment only when the weather is warm Color resembles tundra background in summer