Biology 2012

 In some cases, an intermediate phenotype is shown  Neither allele is dominant  In snapdragons, flower color can be red, pink, or white. The heterozygous condition results in pink flowers (or an intermediate trait)  A white snapdragon crossed with a red snapdragon produces all pink offspring  Two pinks crossed together  produce 1/4 white, 2/4 pink, and 1/4 red  Try These Crosses in your Notes!

Sickle cell disease is incompletely dominant in humans. AA x aa = Aa (sickle cell trait), where some blood cells will have abnormal shapes

In Andalusian fowls, black individuals (B) and white individuals (b) are homozygous.  A homozygous black bird is crossed with a homozygous white bird. The offspring are all bluish-gray. Show the cross as well as the genotypes and phenotypes of the parents and offspring.  What results if a black individual is crossed with a bluish-gray individual? (SHOW YOUR WORK)

 Both alleles can be expressed  For example, red cows crossed with white will generate roan cows. Roan refers to cows that have red coats with white blotches.  This phenotype might seem to support the blending theory. (The blending theory predicts pink F1 progeny.)  The phenotypic outcomes for cow color and incomplete dominance in general can be explained biochemically.  One allele of the gene codes for an enzyme that functions in the production of the red color. The other allele codes for the gene to make white color. If both alleles are present, both are expressed, resulting in a cow that has some red and some white.

In shorthorn cattle, when a red bull (RR) is crossed with a white cow (WW), all the offspring are roan—a spotted, red and white or milky red color.  What offspring are expected from mating a roan bull and a roan cow?  What phenotypes would you expect from a cross between a red bull and a white cow?

 In humans, there are four blood types (phenotypes): A, B, AB, and O  Blood type is controlled by three alleles. A, B, O  O is recessive, two O alleles must be present for the person to have type O blood  A and B are codominant. If a person receives an A allele and a B allele, their blood type is type AB

 Crosses involving blood type often use an I to denote the alleles - see chart.  When doing blood type crosses, you will need to know whether a type A or B person is heterozygous or homozygous. Type O's are automatically OO and type AB is automatically AB. Crosses are performed the same as any other.

 Blood type determines what antibodies are located within the blood.  Type A =B antibodies.  If type B blood is put into their bodies, their immune system reacts as if it were a foreign invader, the antibodies clump the blood - can cause death.  Type AB blood has no antibodies, any blood can be donated to them="universal acceptors"  Type O blood has no surface markers on it, antibodies in the blood do not react to type O blood, ="universal donors"