Incomplete Dominance

Vivian R. SmithE. 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

R R

W

W

RW RW

RW RW

Genotypes

Red

RR

White

WW

Pink

RW

100% of the offspringPink 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 1N N

S

S

NS NS

NS NS

Do the offsprings have Sickle Cell Disease?

Example 2N S

N

S

NN NS

NS SS

What percentage of the offsprings have Sickle Cell Disease?

Resources• Red Four-O-Clock

http://www.dkimages.com/discover/previews/927/703437.JPG• White Four-O-Clock

http://www.fireflyforest.com/flowers/whites/white75.html• Pink Four-O-Clock

http://davie.tv/DavTV/images/2006/4oClock.JPG• Sickle Cell http://www.thirdage.com/healthgate/Images/si55551158.jpg

http://www.defiers.com/scd.html