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UM BIOB 272 - Sex Cont... Dominance
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BIOB 272 1st Edition Lecture 8 Outline of Last Lecture Meiosis, Sex DeterminationI. What is sex? (in a genetic sense)II. Asexual Reproduction in bacteriaIII. Bacteria acquire new DNA three main waysIV. Genetic Transmission in Diploid, Sexual, Eukaryotesa. Cycleb. Genomes (in humans):c. Chromosomes V. Mitosis VI. Meiosis (germinal cell division): VII. Sex Determination- Animal Male/Female Sexes Determined bya. Environmental Factorsb. Chromosomal Factorsi. XY (mammals, Drosophila)ii. ZW (butterflies, birds)iii. XO (some insects)iv. Haplodiploidy (bees, ants, etc.) c. Anisogamy d. Plants ReproductionVIII. Clicker QuestionOutline of Current Lecture These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Sex Cont… DominanceI. A few more Examples of Sexual Reproductiona. Anisogamyb. HermaphroditesII. Chromosome Theory of InheritanceIII. Key Features of X-linked InheritanceIV. Molecular Basiss of Dominance-Recessivity:V. Metabolic PathwaysVI. Genotype/Phenotype Relationship- Co-dominance- Multiple alleles- PleiotropyVII. Multiple LociVIII. Genes and Environment: Expression VariationCurrent LectureSex Cont… DominanceI. A few more Examples of Sexual Reproduction:a. Anisogamy: Sexual reproduction involvingthe fusion of two dissimilar gametes.i. Larger gametes are defined as femaleii. Smaller gametes are defined as maleb. Hermaphrodites:male and female in same individual.i. More than 90% of plants- less than 10% of all plants have separate sexes. Hermaphrodites are very rare in animals.II. Chromosome Theory of Inheritance:a. 1902 - Observation that chromosomes followed sameMendelian rules as gene/traits in many organismsb. 1910 - T.H. Morgan => discovery of sex-linked genes*Studies of white-eye mutants in Drosophila (Nobel Prize winner in 1933)-Drosophila: populargenetic modelorganism-small, short generationtimes (10-12 days), sexually dimorphic&easy to cross-many visiblemutants-studied the white-eyed flies: a. parents= white-eyed male, red-eyed femaleb. F1= No white-eyed fliesc. F2= males about 1:1 white:redfemales all red** “Wild-type”- most common functional variant, in this case red-eyeIII. Key Features of X-linked Inheritance:- The sex of the affected parent (and offspring sex) determines transmission, so reciprocal crosses are different & recessive phenotype is generally more commonin males.IV. Molecular Basiss of Dominance-Recessivity:- Often, a recessive allele is a “loss-of function” mutation, so heterozygotes make ½ as much proteinV. Metabolic Pathways:1. Exceedinglycomplex. High connectivity helpsto buffer effects of 50%decrease in proteinactivity.2. Pathways can beredundant, and theremay be multiple copiesof same gene.3. Many enzymes are present in excess. Flux through a metabolic pathway appears, in many instances, not to be limited by amount of any singleenzyme (as long as some functional enzyme ispresent).- Flux, rate at which precursor transformed to product -Flux through simple, linear pathways may notdrastically affected by 50% reduction in enzyme.VI. Genotype/Phenotype Relationship:- Genotype (genetic constitution) => Actions of other genes/products+ environmental influences and random developments =>Phenotype (expression ofphysical trait)- Many traits do not show simple dominance ofone allele over another, A > ao Incomplete dominance, additivityo Co-dominanceo Multiple alleleso Epistasiso Pleiotropyo Environmental influenceso Genes segregate as before, but traits do not.- Genes segregate as before, but traits do not.- Incomplete dominance or additivityo Heterozygotes have intermediate phenotypeo In whippets, the “bully” trait is caused by a “mostly”recessive allele at a single gene, Myostatin.- Co-dominance: Heterozygotes, Hz, express both traitso Ex. sickle cell trait in humans- Multiple alleles: Many genes have > 2 alleles perlocus, often with complex dominance relationships- Pleiotropy:One gene affects multiple traitso EX: sickling allele for β hemoglobinVII. Multiple Locib. Sometimes gene products from different locimay interact with each other to produceunexpected results.c. Epistasis occurs when the phenotypicexpression of one gene is affected by theaction of another gene.VIII. Genes and Environment: Expression Variationd. Incomplete penetrance - sometimes the traitpredicted by a genotype just does not occur(ex. dominant polydactly)- Example:polydactylypp = normal,Pp, PP = polydactylSome Pp not polydactylousPenetrance ~70%e. Expressivity - sometimes traits areexpressed to different degrees (ex. Diseaseseverity)f. Both of these phenomena probably reflectcomplex interactions of genes with othergenes and the environmentg. Gene expression can depend on temperatureExample: Tyrosin=> L-DOPA => Melaninh. Baldness is sex-influencedDominant in males, recessive in females-related to relative levels of male sex hormones-Autosomal, not sex-linked*, rather sex-influenced-There are other forms of baldness that are sex (X)


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UM BIOB 272 - Sex Cont... Dominance

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