BIOL 3451 1st Edition Lecture 6 Outline of Last Lecture I. 4.1 Alleles Alter Phenotypes in Different Ways II. 4.2 Geneticists Use Variety of Symbols for Alleles III. 4.3 Neither Allele is Dominant in Incomplete, or Partial, Dominance IV. 4.4 In Codominance, the Influence of Both Alleles in a Heterozygote Is Clearly Evident V. 4.5 Multiple Alleles of a Gene May Exist in a Population VI. 4.6 Lethal Alleles Represent Essential Genes VII. 4.7 Combinations of Two Gene Pairs Involving Two Modes of Inheritance VIII. 4.8 Phenotypes Are often Affected by More Thank One Gene Outline of Current Lecture I. 4.8 Phenotypes Are Often Affected by More Thank One GeneII. 4.9 Complementation Analysis Can Determine If Two Mutations Causing a Similar Phenotype Are Alleles of the Same GeneIII. 4.10 Expression of a Single Gene May Have Multiple EffectsIV. 4.11 X-Linkage Describes Genes on the X ChromosomeV. 4.12 Sex-Limited and Sex-Influenced Inheritance, and Individual’s Sex Influences the PhenotypeVI. 4.13 Genetic Background and the Environment May Alter Phenotypic ExpressionVII.Current LectureI. 4.8 Phenotypes Are Often Affected by More Thank One Gene- Most phenotypes come from many pathways of different enzymesi. More commonii. Affected by more than one geneiii. Mendel only reliable within genotypes, not from genotype to phenotype- Epistasis: one gene’s alleles mask the effects of another gene’s alleles i. Describes situation in which a gene can mask the phenotypic effects of another geneii. Often arise because two or more different proteins participate in a common cellular function1. Colorless precursor (enzyme C) colorless intermediate (enzyme P) purplepigment - Recessive epistasis: Dominant allele in one genetic locus masks the expression of the alleles in the second locusThese 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.i. Summer squash: much more complicated1. Includes color, shapeii. Coat color in mice1. Agouti is wt and caused by alternating band of pigment on each hair2. Black is recessive to agouti3. B locus mutation can eliminate all colorII. 4.9 Complementation Analysis Can Determine If Two Mutations Causing a Similar Phenotype AreAlleles of the Same Gene- Novel Phenotypes: Fruit shape in Summer Squashi. 9:6:1 1. Mendel still right here, something caused the 3:3 genotypes to become one (6) which results in 9:6:12. Disc fruits require dominant alleles at both loci3. Sphere need dominant allele at one/either locus4. Long fruits have no dominant allele at either locusIII. 4.10 Expression of a Single Gene May Have Multiple Effects- Pleiotropy: occurs when expression of a single gene has multiple phenotypic effectsi. Ex. Porphyria variegate1. Can’t metabolize porphyrin; deep red urine2. Becomes toxic to brain (begin to become delirious, and other physiological effects) 3. King George III of England may have suffered from this condition4. Not one step, what you put in blood stream, where, how much= complicationIV. 4.11 X-Linkage Describes Genes on the X Chromosome- X,Y system used for sex determination by many animal and plant speciesi. X : large chromosome and encodes many genesii. Y: small chromosome with few genes (not homologous to X, but is similar in spots for pairing purposes)iii. X does not mean female, and Y does not mean male, not for every speciesiv. In mammals : XX= female; XY = male1. Males only get 1 copy of the genes since they only have 1 X chromosome= sex dependent- If you have only 1 copy of an autosome(called a syndrome), then you are dead- Thomas Hunt Morgan discovered X linkage in white eyed mutation Drosophila (fruit flies)i. Figure 4.12; Figure 4.13ii. Reciprocal crosses between white and red did not get identical resultsiii. White locus present on X chromosomeiv. Many traits controlled by X chromosome-linked traits1. Red/green colorblindness2. Homophelia3. Only females are carriers of recessive allelesa. Males are hemizygous (they are expressed in males)v. Lethal X linked recessive disorders are observed only in malesvi. Females can only be heterozygous carriers that do not develop the disorders (but she won’t be athletic, may tire easy, her muscles still don’t work properly, but she isn’t as “abnormal” as the son)1. Ex: Duchenne muscular dystrophya. Onset prior to the age of 6 and lethal around 20 so don’t usuallyreproduceV. 4.12 Sex-Limited and Sex-Influenced Inheritance, and Individual’s Sex Influences the Phenotype- Sex-limited inheritance: occurs in cases where the expression of a specific phenotype is absolutely limited (only) to one sexi. Something wrong with sperm, doesn’t matter to females- Sex-influenced inheritance: sex of individual influences the expression of a phenotype that is not limited to one sex (different in males than in females)i. Feathers in male and female chickens1. Hen-feathering dominant in both sexes2. Cock-feathering recessive only expressed in males3. Actual expression can be changed depending on sex hormoneii. Pattern baldness in humans1. Caused by autosomal genea. Appears as dominant in males and recessive in femalesb. Appears to be related to level of male sex hormonesc. In females, rare tumor can cause excess male sex hormones which then would produce baldness in femalesiii. Other sex influenced traits: breasts and beardsVI. 4.13 Genetic Background and the Environment May Alter Phenotypic Expression- Penetrance: the percentage of individuals that show at least some degree of expression of the mutant genotype in a populationi. Bb: has a phenotype like this 35% of time and something else the rest of the timeii. Partial penetrance: not all people with same genotype have same phenotype- Expressivity: range of expression of mutant phenotype i. Can be result of genetic background differences and/or environmental effects- Dominant allele not expressed in a heterozygote individuali. Autosomal dominant traitii. Affected individuals have additional fingers and/or toesiii. A single copy of the polydactyl allele is usually sufficient to cause this conditioniv. In some cases, however, individuals carry the dominant allele but do not exhibit the traitv. Example:1. Eyeless mutation in Drosophila a. Reduce eye size - *Molecular explanation of expressivity and incomplete penetrance may not always be understood*- Often, differences in phenotypes due to influences