NonMendelian Inheritance Not all traits exhibit simple dominant

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 Mom HH HH x H H h Hh Hh Straight Hh Wavy hh Curly 100% Wavy hh Hh

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 Mom BW BB x Black BW Andalusian WW White WW B W BW 50% Andelusian; 50% White W WW WW

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) wildtype himalayan http: //www. catsandrabbitsandmore. co m/home http: //pantransit. reptiles. org/ima ges/1998 -02 -07/ chinchilla albino http: //didiermervilde. bestofbreeds. net/cavi aandrabbits. html http: //biomesblog. typepad. com/the _biomes_blog/2004/06/

Multiple Alleles • Human Blood Type A B 3 alleles -- I , 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 Dad x Mom genotype? I I I Type A blood can be IAIA or IAIO A A B IA - IA IA- IB IAIB Type B blood can be IBIB or IBIO Type AB blood is IAIB - codominant state Type O blood is IOIO Yes Dad must be IAIO IB-

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 Color resembles tundra background • Some alleles are in summer heat-sensitive – Arctic foxes, cats, rabbits make fur pigment only when the weather is warm