Incomplete Dominance Vivian R. Smith E. B. Aycock Middle School

Incomplete Dominance A form of intermediate inheritance in which heterozygous alleles are both expressed, resulting in a combined phenotype.

An incomplete dominance example, both the instructions for “make red” and the instructions for “make white” are carried out. The result is PINK.

Example A RED Four-o-Clock flower and a WHITE Four- O-Clock flower are cross pollinated. What are the possible offsprings?

RR X WW Red Four-O-Clock White Four-O-Clock

RR W W RW Genotypes Red RR White WW Pink RW

100% of the offspring Pink Four-O-Clock flower

Sickle Cell Example

Red Blood Cells Normal Cells Disc shaped Soft and jelly like Can move easily through the blood vessels Lasts 120 days Sickle Cells Sickle-shaped Hard Can not easily move through blood vessels. Clogs the vessels and can stop blood flow. Lasts 60 days, which causes a lack of hemoglobin and oxygen Affects mainly people of African, Mediterranean, India, Middle East decent

Blood Cells and Genetics Normal Cells: NN –Normal cells, disc shaped Sickle Cell Trait: NS –Carries the gene for sickle cell but does not show signs Sickle Cell Disease: SS –Has Sickle Cell Anemia and suffers from complications

Example 1 NN S S NS Do the offsprings have Sickle Cell Disease?

Example 2 NS N S NN NS SS What percentage of the offsprings have Sickle Cell Disease?

Resources Red Four-O-Clock White Four-O-Clock Pink Four-O-Clock Sickle Cell