Genetics After Mendel

Genetics After Mendel

Genetics After Mendel Single factor inheritance Mendel found traits as dominant or recessive Some instances where the former rule does not apply: Incomplete Dominance Co-dominance Multiple Alleles

Incomplete Dominance A blending of the two traits occur, giving an intermediate expression.

Incomplete Dominance Different alleles of a gene are expressed in the heterozygous condition to produce an intermediate phenotype

Co-dominance P RR WW Both alleles for a trait are dominant Both alleles are expressed in the heterozygous individual F1 RW A red bull crossed with a white cow produces a roan calf

My genotype is RW and my phenotype is roan!

RW RW Co-dominance F1 F2 Roan has intermingled white and red hair RR RW RW WW 1:2:1 phenotypic ratio

Multiple Alleles A pattern of inheritance when a gene may have more than two alleles for any given trait. Ex. Human Blood Types

ABO BLOOD TYPES The letters refer to two different kinds of molecules (antigens), type A and type B present on the surface of red blood cells (RBC). The ABO blood type system uses the presence or absence of these molecules to categorize blood into the four types.

ABO BLOOD TYPES There are 4 different phenotypic blood groups: 1. A has antigen A on RBC (red blood cell) 2. B has antigen B on RBC (red blood cell) 3. AB has BOTH A and B antigen on RBC 4. O has no antigen

Positive or Negative? Another level of specificity is added to blood type by examining the presence or absence of the Rh factor (a protein). Each blood type is either positive + (has the Rh protein) negative - (no Rh protein). For example, a person whose blood type is A positive (A +), has both type A and Rh proteins on the surface of their red blood cells.

BLOOD TYPE IS GENETIC... Blood type is an example of multiple alleles since it involves 3 possible alleles for a gene. A B O The A and B antigen molecules on the surface of red blood cells are produced by two different alleles of the same gene: allele A and allele B. A third version of this gene, the O allele, codes for a protein that is not functional and does not produce surface molecules.

Two copies of the gene are inherited, one from each parent. A and B are CODOMINANT and O is recessive. Rh + is dominant to Rh -. The possible combinations of alleles produce blood types in the following way: Phenotype A B AB O Genotype AA or AO BB or BO AB OO

WHO S YOUR DADDY?? PATERNITY CASE QUESTION Minnie Mouse has type O blood while her husband Mickey mouse has type A blood. Baby Mickey Jr. has type B blood. Mickey Mouse suspects that frisky Donald Duck (type AB blood) may be the biological father of Mickey Jr. Given this information (& ignoring species differences), can you solve this paternity dilemma for troubled Mickey? Show all possible punnett squares as evidence to support your answer.

Another example... Daddy is AB- and mommy is O+. What would all the possible offspring s blood type be?

WHEN BLOOD TYPES MIX Blood plasma is packed with proteins called antibodies. The body produces a wide variety of antibodies that will recognize and attack foreign molecules that may enter from the outside world. When conducting a blood transfusion, it is important to attain compatibility between the antigens present on the RBC of the donor and the antibodies present in the recipient s plasma. If the antibodies present in the recipient s plasma recognize the donor s antigens as foreign, an immune response will be triggered resulting in blood clotting or agglutination.

AGGLUTINATION Blood Transfusion Blood Type (phenotype) Genotype Antibodies in recipient Type A AA or AO Antibody B Type B BB or BO Antibody A Type AB AB None Type O OO Antibody A and B

People with type O blood are universal donors because there are no antigens on the surface of the red blood cells that can trigger an immune response. People with type AB blood are universal recipients because they do not have any antibodies that will recognize type A or B antigens.

A person with Rh+ blood does not have Rh antibodies, therefore, you can always give Rh- blood to an Rh+ recipient. A person with Rh- blood can develop Rh antibody if given Rh+ blood, therefore, you cannot give Rh+ blood to an Rh- recipient. AB+ is the universal recipient because it can receive all blood types due to the fact the recipient does not have antibodies present. O- is the universal donor because it can be given to all blood types due to the absences of antigens on the surface of RBCs. O- can only receive O-.

Homework: Page 196: 1-3 and 6-8