Non-Mendelian Genetics

Non-Mendelian Genetics

• Some traits don’t follow the simple dominant/recessive rules that Mendel first applied to genetics.

• Traits can be controlled by more than one gene.

• Some alleles are neither dominant nor recessive.

Incomplete Dominance

• One allele is not completely dominant over another.

• The heterozygous phenotype is a blending of the two homozygous phenotypes.

Example: four o’clock flowers• rr=red• ww=white• rw=pink (blending of the two alleles)

Codominance

• Two alleles are both expressed as a dominant phenotype

• Coat color in cows– RR: Red– WW: White– RW: Roan, white with

red spots (NOT pink!)

Multiple-Allele Series

• Codominance• More than two choices of alleles are present for a

trait• ABO blood type has three alleles• ABO Blood types:

– If both A and B are present, type is AB– Neither is recessive

• Individuals can be type A, B, AB, or O (recessive)

What is blood made up of?• The red blood cells

– contain hemoglobin. – Red blood cells transport O2 and CO2

to and from body tissues.

• The white blood cells– fight infection.

• The platelets– help the blood to clot

• The plasma – Fluid which contains salts and

various kinds of proteins.

Determining Blood Type

• Protein molecules found on the surface of RBC’s and in the blood plasma determine the blood type of an individual.– Antigens are located on the surface of the

red blood cells– Antibodies are in the blood plasma.

                                                                                             

(not actual shape or size of antigens)

                                                                                             

(not actual shape or size of antigens)

                                                                                             

(not actual shape or size of antigens)

What are the different blood groups?

• Blood group A (IA, IA ), (IA, i)

have A antigens on the surface of red blood cells and B antibodies in blood plasma.

• Blood group B (IB, IB ), (IB, i)

have B antigens on the surface of red blood cells and A antibodies in blood plasma.

What are the different blood groups?

• Blood group AB (IA, IB )

have both A and B antigens on the surface of red blood cells and no A or B antibodies in blood plasma.

• Blood group O (i, i) have neither A or B antigens on the surface of red blood cells but have both A and B antibodies in blood plasma.

Blood transfusions – who can receive blood from whom?

• The transfusion will work if a person who is going to receive blood has a blood group that doesn't have any antibodies against the donor blood's antigens.

• People with blood group 0 are called "universal donors" and people with blood group AB are called "universal receivers."

Rh Factor

• Refers to another antigen on red blood cells

• Dominant trait is to have the antigen– Rh+

• Recessive trait is not to have it– Rh-

• A person with Rh- blood will produce antibodies to Rh+ blood

• Can be a problem in pregnancy

Sex-Linked Inheritance

Review

• Males have an X and a Y chromosome

• Females have two X chromosomes

• These chromosomes determine sex, so genes located on these chromosomes are known as sex-linked genes.

• The X chromosome is much larger than the Y, so it carries more genes than the Y chromosome.

•Disorders that are sex-linked are much more common in males, because they would only need 1 recessive allele to have the trait; rather than the two recessive alleles the females need.

Hemophilia

• Recessive trait

• Disorder where individuals are missing the normal blood clotting protein.

• Uncontrolled bleeds from minor cuts or bruises.

• Female genotype:

• Male genotype:

Colorblindness

• Recessive

• Inability to see certain colors

• Female genotype:

• Male genotype:

Duchenne Muscular Dystrophy

• Recessive

• Progressive weakening and loss of skeletal muscle.

• Defective version of gene that codes for muscle protein

• Female genotype:

• Male genotype:

• EXAMPLES!!

• A woman who is heterozygous for normal vision marries a man who is colorblind. What are the chances of them having a son or daughter who is colorblind?

**NOTE: You have to use X’s and Y’s, and read the punnett square separately for boys and girls!**

• A woman who is homozygous for normal blood clotting marries a man who has hemophilia. What are the chances of them having a son or daughter with hemophilia?