BIOL 3451 1st Edition Lecture 5 Outline of Last Lecture I. 3.3 Mendel’s Dihybrid Cross Generated a Unique F2 RatioII. 3.4 Trihybrid Cross Demonstrates that Mendel’s Principles Apply to Inheritance of Multiple TraitsIII. 3.5 Mendel’s Work was Rediscovered in the Early Twentieth CenturyIV. 3.6 Independent Assortment Leads to Extensive Genetic VariationV. 3.7 Independent Assortment Leads to Extensive Genetic VariationVI. 3.8 Chi-square Analysis Evaluates the Influence of Chance on Genetic DataVII. 3.9 Pedigrees Reveal Patterns of Inheritance of Human TraitsOutline of Current 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 Current LectureChapter 4: Intro- Neo-Mendelian genetics (extensions from his original experiments)o The exceptions/extensionso These ratios did not conform to what Mendelian did beforeI. 4.1 Alleles Alter Phenotypes in Different Ways- Alleles: alternative forms of a gene are called…o Mutant form of gene that causes differences- Mutation: source of all alleles- Wild-type: most frequently occurring in natureo Doesn’t mean it’s the best, maybe at one time it was, but not now…adaptationo Frequently are dominant, but not always….i.e. Huntington allele (Huntington’s disease)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.- Mutationo Without it, you would be limited to what you have right then and there….there would be no variation, no evolution……we would still be slimes on the groundo Genetic info is modified Often produces altered gene product, but not always, some are regulatory which affects where it goes, how much, o New phenotypes result from changes in functional activity of gene product Eliminating enzyme/protein function Changing relative enzyme/protein efficiency Changing overall enzyme/protein functionII. 4.2 Geneticists Use Variety of Symbols for Alleles- Dominanto Italic, uppercase letter (D) oro Letters (Wr)- Recessiveo Italic lowercase letter (d) oro Italic letter or group of letters with the + superscript (Wr+)- Alleles in Drosophiilao e+/ e+: gray homozygote (wild type)o e+/e: gray heterozygote (wild type)o e/e: ebony homozygote (mutant)- if no dominance, italic uppercase letters and superscripts are used to denote alternative alleles (R1, R2, CW, CR)- Phenotypic trait may be influenced by more than one gene and the allelic forms of gene involvedo Need so many to get what you want i.e. just because you have the purple gene (P), you also need genes L, M, N, O, P in order to be expressed in phenotype- Wild-type alleles: prevalent alleles in populationo Typically encode proteins that  Function normally Are made in right amounts (very critical)- Take wild type and mutates: mutant alleleso Sacrifice many individuals for the sake of making 1 that is better for future generationso Remember not everything alters everythingo These tend to be more rare (may not be uncommon, just not as much as wild type) Blood types: Wild type-O, Rare types: A, B (but not uncommon)o Mutant alleles are often inherited in recessive fashiono Cause reduction in amount or function of encoded protein (that’s why not usually so good)III. 4.3 Neither Allele is Dominant in Incomplete, or Partial, Dominance- Incomplete/partial dominance: offspring is cross between parents with contrasting traits may have intermediate , kind of like a blend (although, they don’t mix bc the original colors will come back)o Phenotypic ratio is identical to the genotypic ratioo i.e.: red snapdragon crossed with white snapdragon f1 offspring have pink flowers f2 generation: .25 red, .50 pink, .25 white- Incomplete dominance in humanso Heterozygotes exhibiting wild-type phenotype may have intermediate level ofgene expression Ex: Tay-Sachs disease- Begin as normal, then phenotype craters and die (homozygousrecessives die when hexosaminidase activity absent)- Heterozygotes appear normal but have .5 of wt enzyme activity when compared to homozygous normal non-carriers o Threshold effect: lots of capacity, more than you need…comes about if normal phenotypic expression occurs whenever a certain level (usually 50% or less) of gene product is attained/ 50% is good number Can be good idea to build in excess capacity so when you get part of Tay-SachsIV. 4.4 In Codominance, the Influence of Both Alleles in a Heterozygote Is Clearly Evident- Codominance: two alleles at a locus produce different and detectable gene products in heterozygote (AB blood type)o No dominance or recessive o No “blended” phenotype (incomplete)o Ex. MN blood group in humansV. 4.5 Multiple Alleles of a Gene May Exist in a Population- Multiple alleles of gene in a populationo Individuals can have up to 2 alleles for a single gene (hundreds of alleles)o Multiple alleles applies when there are three or more alleles of the same gene in a population Any gene- Human ABO blood groups provide example of multiple alleles in a populationo A and B antigens present on surface of blood cells Controlled by gene on chromosome 9 (sugars are more antigenic, more important)o Figure 4.5 Notice how they write the blood types (I)o IA allele gives enzyme that can add terminal sugar N-acetylgalactosamine to the H substance (substrate specificity!!o IB gives modified eo O one doesn’t add anything or bind anything: o Figure 4.2!!! If don’t make H, then can’t make A, B because you can’t put antigen on something that isn’t there, (H is the foundation)- Bombay phenotypeo Woman typed as type O, but One parent has type AB blood and She is an obvious IB allele donor to two childreno Woman found to be homozygous FUT1 at the fucosyl transferase locus No fucose on H substance; no substrate to make A or B antigens Even though, PP, if you don’t have the other 24 genes, then it won’t work!  Figure 4.3- The A and AB at the top carry the