8.2 Alleles and Genes Interact to Produce Phenotypes AP Biology Radjewski

Mutations Rare inherited changes in the genetic material Occur in genes One allele can be mutated to a different allele

Incomplete Dominance Many genes have alleles that are neither dominant or recessive to one another. There is an intermediate phenotype (Blend) Example – snapdragons – RR = red – WW – white – RW = pink! Example: Cross a red flowered Japanese 4:00 plant with a white flowered 4:00 plant

Incomplete Dominance Example Genotype: 100% RW Phenotype: 100% pink

Blood Types - Codominance Codominance – Two alleles of a gene share dominance and are both expressed In humans there is a gene I that encodes an enzyme involved in the attachment of sugars to a glycoprotein on the surface of red blood cells There are 3 alleles of the gene: I A, I B, and I O. The I A and I B alleles both encode active enzymes, but the enzymes attach different sugars to the glycoprotein.

Blood Types Continued The I O allele does not encode an active enzyme, so no sugar attaches When two different alleles are present, both alleles are expressed. The A and B glycoproteins are antigenic, which means the recipient will mount an immune response and produce antibodies against the nonself A or B cells. The O glycoprotein does not provoke any immune responses. This makes people with I O I O good blood donors

TypeAntigen of RBC Antibodies in plasma Can receive from Can donate to AABO,AA, AB BBAO.BB, AB ABA,BNoneO, A, B, AB AB ONoneA,BOO, A, B, AB

Rh Factors Rh factors are another antigen on the surface of the RBC’s If you have this antigen/protein, you are said to be Rh+ and if you don’t have it you are Rh- Dangerous in pregnant women who are Rh- carrying a Rh+ child During delivery, the blood mixes, so the mother will produce antibodies and the first child is unharmed But if the second child is also Rh+, then those antibodies will attack the child’s blood cells causing severe complications – Can be treated in early pregnancy – Otherwise child will not be able to produce RBC’s and that makes oxygen levels low and death could result.

Cross a person with bloodtype AB with a person with bloodtype O

Codominance Example I A I B x I o I o IAIA IBIB IoIo IoIo IAIoIAIo IBI o IAIoIAIo IBIoIBIo Genotype % 50% I A I o 50% I B I o Phenotype % 50% bloodtype A 50% bloodtype B

Epistasis Phenotypic expression of one trait is affected by another gene Example in labrador retrievers – Allele B (black) is dominant over b (brown) – Allele E (pigment deposition in hair) is dominant to e (no deposition, so hair is yellow) An EE or Ee dog with BB or Bb is black; one with ee is yellow regardless of the dominant B