COMPLEX PATTERNS OF INHERITANCE Patterns of inheritance that do NOT follow Mendel’s law.

Review Mendel’s Simple Genetics There are 2 alleles for each trait. An allele is either Dominant Which is represented by upper case, D. The phenotype is visible w/just one allele. So the phenotype is visible with either a heterozygous or a homozygous genotype. Or Recessive Which is represented by lower case, d. The phenotype is visible ONLY w/2 recessive alleles: that’s the homozygous recessive genotype.

Review Mendel’s Simple Genetics Mendel’s Law of Segregation: these alleles will separate from each other during the formation of gametes. Mendel’s law of Independent Assortment: theses alleles will be assorted into the newly formed gametes independently of each other.

Incomplete Dominance The phenotype of the heterozygote is in between those of the two homozygotes. –It is an intermediate, and a third phenotype appears when the heterozygote is present –In heterozygotes, neither allele is completely dominant.

Example-Snapdragons RR = Red R’R’ = White RR’ = Pink R R R’

CODOMINANCE The phenotypes of both alleles are equally expressed in the heterozygote. –Example: Horses H R H R = Red Horse H W H W = White Horse H R H W = Roan Horse H R HWHWHWHW

Red Horse White Horse Roan Horse CODOMINANCE

Multiple Alleles Traits controlled by more than 2 alleles (more than 2 phenotypes) A diploid individual can only have 2 alleles of a trait. –Example: Blood type = 3 different alleles: I A, I B, i

Blood Type Blood Type That Can Be Received Type of Antigens Present Type of Antibodies Produced A ( I A )A and OA antigensB antibodies B ( I B )B and OB antigensA antibodies O ( i ) Universal Donor Only ONo antigens A and B antibodies AB ( I A I B ) Universal Recipient All types A and B antigens No antibodies Multiple Alleles

H R H R HRHRHRHR Genes can be on the same chromosome or on different chromosomes. Phenotypes usually show a continuous range or variability. - Example: Height = A, B, and C all contribute to height. Polygenic Traits

AaC c Bb Tallest = AABBCC Shortest = aabbcc In between = AbBbCc Polygenic traits include: skin color, body weight, eye color, hair color, and height. Polygenic traits