Exceptions to the Rule Not all of Mendel’s rules apply to all genes. Sometimes more than one allele is dominant Sometimes neither allele is dominant or recessive Other times genes are carried on multiple alleles (more than 2 options!)

Codominance Two alleles are both expressed as a dominant phenotype Both are seen at the SAME time! Coat color in cows RR: Red WW: White RW: Roan, white with red spots

Codominance Example RW WW RW WW R W W Coat color in cows displays codominance. Use the Punnett Square to determine the possible phenotypes of offspring of a white cow with a roan cow. R W W RW WW RW WW

+ Allele for Black cat (B) Codominance More examples of Codominance = Tabby cat (BT) Allele for Tan cat (T) + Allele for Black cat (B)

Codominance = Black & White Chicken More examples of Codominance (BW) Allele for White chicken (W) + Allele for Black chicken (B)

Incomplete Dominance Sometimes one allele is not completely dominant over another. Called incomplete dominance The heterozygous phenotype is a blending of the two homozygous phenotypes.

Incomplete Dominance Examples: Four o’clock flowers rr=red ww=white rw=pink (blending of the two alleles)

Incomplete Dominance Example Flower color in four o’clock flowers displays incomplete dominance. Use the Punnett Square to determine the possible phenotypes of offspring of a pink flower with a red flower. r w r rr rw rr rw

Incomplete Dominance Examples: Rabbits ll= long fur (angora rabbits) ss= short fur (rex rabbits) ls=medium length fur (blending of the two alleles)

Multiple Alleles More than two allele choices are present for each trait. Example: Coat Color in Rabbits (4 possible alleles!) Cch = chinchilla C = full color c = no color Ch= Himalayan color

Multiple Alleles Coat Color in Rabbits C=full color Cch= chinchilla Ch= Himalayan color c = no color There is a hierarchy of dominance for this trait. For example, a rabbit with genotype CCch will have a full coat color. A rabbit with genotype Cch Ch will be chinchilla.

Multiple Alleles ABO blood type has three alleles ABO Blood types: A & B are codominant. If both A and B are present, type is AB Neither is recessive O is recessive to both A and B Individuals can be type A, B, AB, or O Alleles are written IA, IB, or i. If you are heterozygous for type A, your genotype is IA i

Multiple Alleles ABO blood type has three alleles ABO Blood types: If both A and B are present, type is AB (codominance) Neither is recessive Individuals can be type A, B, AB, or O (recessive) Alleles are written IA, IB, or i. If you are type A (heterozygous) your genotype is IA i

Type A Type B Type AB Type O IA IA IA i IBIB IB i IAIB ii Blood Type (Phenotype) Possible Genotypes Type A IA IA IA i Type B IBIB IB i Type AB IAIB Type O ii

What is blood made up of? The red blood cells The white 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.

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 (IBIB ), (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" People with blood group AB are called "universal receivers."

Rh Factor Refers to another antigen on red blood cells Dominant trait (D) is to have the antigen Rh+ Recessive trait (d) is not to have it Rh- A person with Rh- blood will produce antibodies to Rh+ blood Can be a problem in pregnancy – if mother is Rh-, and fetus is Rh+, her blood may begin to break down the blood of her baby!

Rh Factor Refers to another antigen on red blood cells Dominant trait (D) is to have the antigen Rh+ Recessive trait (d) is not to have it Rh-

Sex-Linked Inheritance

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 with hemophilia genotype: Xh Xh Male with hemophilia genotype: XhY

Colorblindness Recessive Inability to see certain colors Female with colorblindness genotype: Xc Xc Male with colorblindness genotype: XcY

Colorblindness

Do any of these pictures look the same?!

Test time!

Duchenne Muscular Dystrophy Recessive Progressive weakening and loss of skeletal muscle. Defective version of gene that codes for muscle protein Female with DMD genotype: Xd Xd Male with DMD genotype: XdY

EXAMPLE!! 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!**

Xc Y XC XC Xc XC Y XcY Xc Xc Xc Woman: XC Xc Man: XcY 50% of females will have normal vision, but will be carriers 50% of females will be colorblind 50% of males will have normal vision 50% of males will be colorblind

Y Xh XH XH Xh XHY XH XHY XH Xh 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? Woman: XH XH Man: Xh Y Y Xh XH XH Xh 100% of daughters will have normal blood clotting, but will be carriers 100% of sons will have normal blood clotting XHY XH XHY XH Xh

JK! Polygenic Traits Sometimes, multiple genes can control traits Normally shows a wide array of phenotypes Example: skin color More than four genes control it…each with at least 2 different alleles Lets try a cross! JK!

Examples of polygenic traits in humans

Example of polygenic traits in humans

Genes and the Environment The characteristics of an organism are not determined solely by the genes that organism inherits. Genes provide the plan for development…but the environment can change how that plan unfolds!

Genes and the Environment Example: Western White Butterfly If hatching in the Spring, wings would be darker than those hatching in the summer. Reasoning… The body temperature of the butterfly has to remain around 28-40 degrees C to fly. It is colder in spring, so they need darker pigment to absorb more heat!