Complete Versus Incomplete Dominance Versus Codominance PreAP Biology

Complete Versus Incomplete Dominance Versus Co-dominance Pre-AP Biology

Bellwork n Speculate on how Type AB blood is inherited. Be ready to share.

Objectives n n n Contrast complete dominance and incomplete dominance Contrast complete dominance and codominance Explain how Blood Types are inherited Construct Punnett Squares for blood type Explain why a Type A person cannot get a transfusion of Type B blood

Key Terminology Complete dominance n Incomplete dominance n Codominance n Antibodies n Agglutination n

Complete Dominance n Definition n n Dominant allele fully expressed in heterozygote and homozygous dominant Ex. Flower color of pea plants

Testcross By looking at a dominant phenotype cannot determine if genotype is homozygous or heterozygous n Do a Testcross n Cross unknown with homozygous recessive n Heterozygous phenotypic ratio of 1: 1 n Homozygous phenotypic ratio of 4: 0 n

Incomplete Dominance n Definition n n One allele not completely dominant over another allele heterozygote will be intermediate to homozygous dominant and homozygous recessive

Ex. Flower Color in Snapdragons

Think-Pair-Share What is blending theory? Why doesn’t incomplete dominance support blending theory? PROPERTY OF PIMA COUNTY JTED, 2010 3

Co-dominance

Codominance n Definition n n Both alleles are fully expressed in the heterozygote at the same time Ex. Human Blood Type AB

ABO Blood Typing n n n One system used to type blood is the ABO Blood Group The 4 blood types are A, B, AB and O These are the 4 different phenotypes of the same trait

Human Blood Types (Cont’d) The ABO blood types are determined by paired combinations of three alleles IA, IB, and i n The letters A and B refer to two genetically determined carbohydrates on the surface of red blood cells n

Human Blood Types

Human Blood Types (Cont’d) Neither IA and IB is dominant over the other n IA and IB are both dominant over i (i=recessive) n When IA and IB are both present they are codominant n n because both are expressed in heterozygotes as Type AB

Human Blood Types (cont’d) n With three alleles, six possible genotypes Blood Type A B AB O Possible Genotypes I A, I A i I B, I B i IA IB ii

Human Blood Types (Cont’d) n Even for traits with multiple alleles, an individual can have only 2 of the possible alleles for that gene

Think-Pair-Share Explain why blood types are an example of codominance. Get ready to share. PROPERTY OF PIMA COUNTY JTED, 2010 3

Blood Transfusion Foreign antigens cause the immune system to produce antibodies n Antibodies react with a foreign antigen to inactivate that antigen n A and B will be antigens if you do not already have those surface carbohydrates n

Blood Agglutination If you have Type A blood and are given Type B blood in a transfusion n The B antigen on the red blood cells in the transfusion will react with your antibodies against the B antigen n Causing it to form a solid (agglutinate) that clogs up the blood vessels n

Think-Pair-Share Explain what would happen if a Type B person gets a transfusion from a Type AB person. Explain what would happen if a Type AB person gets a transfusion from a Type B person.

Donation of Blood

Table 1. Human Blood Types

Sample Problem #1 n Use a Punnett Square to predict the offspring of a cross between a heterozygous Type A and a Type O person. Get ready to share.

Sample Problem #2 n n n Suppose that you are a geneticist and are asked to testify in a paternity case in which the mother is A type blood, the child has O type blood and the alleged father has B type blood Attorney claims that because the child has O type blood and the father has B type blood, his client cannot be the father. Is the attorney’s claim true? Use a Punnett Square to support your answer

Sample Problem #3 n n Sponge. Bob loves growing flowers for his pal Sandy. Her favorite flowers , Poofkins are found in red (RR), purple (Rr) and Blue (rr) What would happen if Sponge. Bob crossed two Poofkins with purple flowers n n What percentage would have red, purple, blue flowers? Does this cross demonstrate complete or incomplete dominance? How do you know?

Problem #4 n In humans, pointed eyebrows (B) are dominant over smooth (b). Bob is heterozygous for pointed eyebrows and is married to Mary who has smooth. n n n What is the phenotypic ratio, genotypic ratio of this cross? Does this cross demonstrate complete dominance or incomplete dominance? What is the probability that the children will have smooth eyebrows?

Problem #5 n A fruit fly with a gray body (B) and red eyes (P) (genotype Bb. Pp) is mated with a fly having a black body (b) and purple (p) eyes (genotype bbpp). n n n Is this a monohybrid or dihybrid cross? What are the different gamete combinations for the two flies? What is the phenotypic ratio, genotypic ratio?

Problem # 6 n A couple are both phenotypically normal (H) but their son suffers from hemophilia (h), a sex linked disorder. n n What are the genotypes of the parents? What fraction of the children are likely to suffer from hemophilia? What fraction of the children are carriers? What fraction of girls versus boys will have hemophilia? Why is one gender more prone to have the disease?

3 Minute Paper You have three minutes to write down the difference between complete dominance, incomplete dominance, and co-dominance Be prepared to share PROPERTY OF PIMA COUNTY JTED, 2010 31