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Chapter 11 Beyond Mendel Conditions that Mendel didn't explore - genetic traits that are inherited in new and interesting patterns Incomplete Dominance Codominance Multiple Allele Traits Epistatic Alleles Sex Determination Polygenic Inheritance Incomplete Dominance Traits appear to "blend" in offspring RR x WW RW (pink) Show: Pink x Red Pink x Pink White x White Figure 11.14 This illustrates another style of "letters" to denote genotypes R1 and R2 Codominance Both alleles in a heterozygous individual are expressed Sickle Cell Trait in Humans Genotypes & Phenotypes SS= not sickle cell Ss= a little sickle cell ss= a lot sickle cell Coloration in Rodents Black x White = Gray BB x WW = BW ROAN COW What happens when you cross a white and a red cow? Roan is codominant - both alleles R and W are expressed What happens when two Roan Cows are Crossed? Blood Types - Multiple Alleles When doing blood type crosses, you will need to know whether at type A or B person is heterozygous or homozygous. Type O's are automatically OO and type AB is automatically AB. Crosses are performed the same as any other. Show Crosses: AB x AO AO x BO AA x AB A woman who is type A is married to a man who is type B, what are ALL of the possible blood types of their children? Many Genes Have Multiple Alleles A population might have more than two alleles for a given gene. In Labrador retriever, coat color is determined by one gene with four different alleles. Five different colors result from the combinations of these alleles. (More on labradors later) • • Eye color is also controlled by multiple alleles LABRADOR RETRIEVERS AND EPISTATIC ALLELES • A population might have more than two alleles for a given gene. • In labrador retriever, coat color is determined by one gene with four • different alleles. Five different colors result from the combinations of these alleles. Even if more than two alleles exist in a population, any given individual can have no more than two of them: one from the mother and one from the father. Black is dominant to chocolate B or b Yellow is recessive epistatic (when present, it blocks the expression of the black and chocolate alleles) E or e Yellow Lab Black Lab Chocolate Lab BBee Bbee bbee BBEE BbEE BBEe BbEe bbEE bbEe 1. A black lab (BBEe) x yellow lab (bbee) 2. A chocolate lab (bbEe) x black lab (BbEe) 3. Two black labs (BBEE x BbEe) Sex Linked Genes Genes located on the X chromosome are inherited with that X. When doing crosses you must include the sex chromosomes in your cross. Use superscript letters for the allele. Example: In fruit flies, eye color is a sex linked trait. Red is dominant to white. Females XRXR XRXr XrXr Males XR Y Xr Y FRUIT FLY CHROMOSOMESDrosophila melanogaster Show the cross between a white eyed male and a red eyed female: XrY x XRXR Show the cross between a red eyed male and a white eyed female: Figure 12.2 Human Sex Linked Disorders 1.Colorblindness 2.Muscular Dystrophy 3.Hemophilia 4.Fragile X Syndrome COLORBLINDNESS More Tests Color Blindness Simulation http://www.idea.org/vision-demo.html?gclid=CJejqJ38_JgCFQ4eDQodUzNEmQ Tests http://www.toledo-bend.com/colorblind/Ishihara.asp Polygenic Traits • Individual heritable characters are often found to be controlled by groups of several genes, called polygenes. • Each allele intensifies or diminishes the phenotype. • Variation is continuous or quantitative (adding up) - also called quantitative inheritance • Seed Color in wheat - aabbcc, Aabbcc, AaBbcc, AaBbCc, AABbCc, AABBCC (light, intermediate colors, dark) • In humans - hair color, height, skin color Pg 197 Polygenic Inheritance AABBCC x aabbcc (P) AaBbCc x AaBbCc (F1) Seven Possible Phenotypes in the F2 Figure 11.16 Figure 11.17 Environment and PhenotypeTemperature, water, food sources can have an affect on how a gene is expressed Rabbits have a gene that codes for darker pigments - this gene is more active at low temperatures. Parts of the body that are colder will develop the darker pigmentation - ears and feet Figure 11.18b