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UB BIO 329 - Chpt 4 Allelic interactions F13

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PowerPoint PresentationSlide 2Allelic interactionsIntragenic allelic interactionsSlide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Wednesday, September 4, 2013Top 5 for today:Allelic Interactions:1)Dominant/recessive relationships2)Incomplete dominance3)Codominance4)Multiple alleles5)Lethal allelesMake sure you can do ALL the Chi-square problems on the lab sheet. Always state null hypothesis, p value used, degrees of freedom, and Chi-square critical value from table. I also highly recommend including a key and diagramming the cross. Review and be sure you know the expected ratios of these crosses:Monohybrid, Dihybrid, Parental , F1 , Test cross, Reciprocal crossQuiz Wednesday, September 4, 20131)If a woman with blood type A married a man with blood type B what possible blood types can their children have? (show possible genotypes and phenotypes).2)A couple, neither of whom have phenylketonuria (a recessive disorder), have a child with phenylketonuria. What is the probability that: a) Their next child will have phenylketonuria? b) Their first two children will have phenylketonuria? c) Their third child will be a carrier for phenylketonuria?Allelic interactions•Alleles–Wild type – allele that occurs most frequently in most populations – arbitrarily designated as normal (often dominant)–Mutation – causes alternate forms of alleles•Loss-of-function- mutation that causes diminution or loss of wt function•Null allele- if loss of function is complete•Gain-of-function- enhances function of wt product – often more product. Often dominant since one copy of mutation in diploid alters normal phenotype•No change in function – neutral•Phenotype effects…–Allelic symbolsIntragenic allelic interactions•Dominance/recessive (complete dominance)–Mendelian interaction–In heterozygotes, one allele completely masks other•Monohybrid cross – F2 ratio 3:1•Dihybrid cross – F2 ratio 9:3:3:1–Rh antigen almost behaves this way Rh+ Rh-Intragenic allelic interactions•Incomplete dominance (partial dominance) – expression of 1 allele–Heterozygote has phenotype intermediate between 2 homozygotes–Because neither is dominant, often number alleles R1, R2, etc. or use other types of superscripts (CW, CR – color white, color red)–Snap dragon color example •Monohybrid cross F2 ratio 1:2:1\•Phenotypic ratio = genotypic ratio•Dihybrid cross when paired with dominance/recessive 3:6:3:1:2:1–Often caused by reduced gene expression for mutant allele–Sickle-cell anemia–Tay-Sachs and threshold effectHorses can be cremello (a light cream color), chestnut (a brownish color), or palomino (a golden color with white in the tail and mane). Of these phenotypes, only palomino never breed true. cremello x palomino ½ cremello, ½ palominochestnut x palomino ½ chestnut, ½ palominopalomino x palomino ¼ chestnut, ½ palomino, ¼ cremelloFrom the results given, determine the mode of inheritance by assigning gene symbols and indicating which genotypes yield which phenotypes.Intragenic allelic interactions•Codominance – expression of both alleles–Heterozygote expresses both alleles–MN blood types – LM LN – chromosome 4 glycoprotein in rbc, 2 forms–LM LM = M phenotype–LM LN = MN phenotype–LN LN = N phenotype–Common for molecular phenotypes (ABO blood types)–Dihybrid cross when paired with dominance/recessive 3:6:3:1:2:1Figure 4-5Intragenic allelic interactions•Multiple alleles–More than 2 possible alleles in population–Still only 2 alleles in any one individual–white locus in Drosophila–ABO bloodtypes – I (isoagglutinogen) alleles on chromosome 9–Blood transfusion – O = universal donor, AB = universal recipientIn rabbits, a series of multiple alleles controls coat color in the following way: C is dominant to all other alleles and causes full color. The chinchilla phenotype is due to the cch allele, which is dominant to all alleles other than C. The ch allele, dominant only to ca (albino), results in the Himalayan coat color. Thus the order of dominance is C > cch > ch > ca. Give the possible genotypes of these parents and offspring. Himalayan x Himalayan albinofull color x albino chinchillaalbino x chinchilla albinochinchilla x albino HimalayanIntragenic allelic interactions•Lethal alleles–Recessive allele – homozygote results in early death – often zygotic – often lack some biochemical necessity–Often heterozygotes have phenotype that distinguishes from homozygous healthy–Example: yellow fur gene in mice 2:1 ratio–Dominant lethal – Huntington’sHeterozygous Cp cp chickens express a condition called creeper, in which the leg and wing bones are shorter than normal (cp cp). The dominant Cp allele is lethal when homozygous. Two alleles of an independently segregating gene determines white (W-) versus yellow (ww) skin color. From matings between chickens heterozygous for both of these genes, what phenotypic classes will be represented among the viable progeny, and what are their expected relative


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UB BIO 329 - Chpt 4 Allelic interactions F13

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