5.2 Variations of Heredity

Pages 194-196

Incomplete Dominance

Occurs when neither allele dominates the other and both have an influence on the individual.

Incomplete dominance results in partial expression of both traits.

Incomplete dominance in impatiens

Incomplete Dominance in Animals

Rex rabbit (short fur)crossed with angora rabbit (long fur)

Punnett Square

Codominance

Occurs when both alleles are expressed fully to produce offspring with a third phenotype.

Codominance in short horn cattle

Blood types

There are 3 alleles for bloodtype:

IA , IB , i

Blood

Alleles

• Each allele codes for a different enzyme that places different types of sugars on the surface of a red blood cell.

There are four types of blood

Type AType B

Type ABType O

Genotypes and Phenotypes

IA IA blood type AIB IB blood type BIA IB blood type ABIA i blood type AIB i blood type Bii blood type O

Antigens

Type A blood has anti-B antigens. If a person with A-type blood receives B-type blood or AB-type blood, it will clot.

Blood types

Blood type O

The universal donor because people with every blood type can receive O-type blood without a danger of it clotting.

Blood Type AB

The universal recipient because people with AB blood can receive any type of blood