Complete Incomplete Codominance Multiple Alleles Sex-linked Traits Forms of dominance Complete Incomplete Codominance Multiple Alleles Sex-linked Traits

Complete dominance Mendel’s garden peas showed complete dominance Tt Example: TT x tt = 100% Tt tall short tall http://www.communityschoolhouse.org/punnettsquares.htm T T Tt tall t t

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Incomplete dominance The dominant allele does not completely cover up the expression of the recessive allele The phenotype of the offspring appears as a blend of the two For example: snapdragons red x white = pink

Incomplete dominance RR x rr Red white R R Rr Pink pink r r

Codominance Two alleles are both dominant If inherited together, both will be expressed

Codominance Black x White BB WW B B BW Blue roan W W

Multiple Alleles Sometimes there is more than two forms of a trait! Example human blood typeshttp://nobelprize.org/medicine/educational/landsteiner/index.html

Ex: Blood type problems What are their possible blood types if a heterozygous type A man and a heterozygous type B woman have children? IAi x IBi IA i IAIB IBi IAi ii 25 % chance for AB, A, B, or O IB i

Blood types and paternity Blood type can only exclude a person from being the possible father of a child Ex: a man accused of fathering a child has type O blood and the child has type AB ii x _____ i i The man can only pass on recessives! He could not possibly have fathered this child

Sex-linked traits Traits that are controlled by genes inherited only on the X sex chromosome

Red-Green colorblindness

XH Xh XH Y Hemophilia XH XH Normal XH Xh carrier XH Y normal Xh Y a hemophilia carrier and a normal man want to know the probability of having children affected by hemophilia http://www.yourgenesyourhealth.org/hemo/inherited.htm Genotype Phenotype for blood clotting XH XH XH Y Normal female Normal male XH Xh Female who is a carrier, she has normal blood clotting Xh Y Male who inherited the recessive allele located on the X sex chromosome will not produce the blood clotting factor XH Xh XH XH Normal XH Xh carrier XH Y normal Xh Y hemophilia XH Y

Polygenic Inheritance occurs when more than one gene controls a single trait these are sometimes called quantitative traits because the number of dominant to recessive alleles creates a wide range of observable phenotypes Example: human height, skin color, eye color http://www.ncbi.nlm.nih.gov

Melananin Production in skin and eyes

Human Height