Biology 151 1st Edition Lecture 22 Outline of Last Lecture 1. Diploid parent can have 2 different alleles of a gene2. Genotype of diploid (zygote) can be...3. Segregation of alleles during meiosis4. What genotype is a flower plant with a purple phenotype?5. What happens if you follow 2 genes at the same time?6. Independent assortment of non-homologous chromosomes7. Independent assortment of chromosomes and probabilities8. Complications with Mendelian inheritance9. Example (of 2) - biochemical synthesis of arginineOutline of Current Lecture 1. What if one phenotype is caused by more than 1 gene?2. What if 2 genes are on the same chromosome?3. Thomas Hunt Morgan (1866-1945)4. Do 2 genes on the same chromosome get inherited together?5. Distance between "linked" genes on chromosome determines the frequency of crossing over 6. Mapping mutated genes by recombination7. Fine-scale mapping of mutations using crossing overCurrent Lecture- incomplete dominance = heterozygote has phenotype that is intermediate between that of homozygotes- codominance = different alleles give different dominant traitsWhat if one phenotype is caused by more than 1 gene?:- ex. biochemical synthesis of arginine- 3 genes coding for 3 different enzymes in different steps of synthesis pathway- bread mold is haploid- if 'r' allele produce enzymes that have slightly reduced catalytic activity- inheritable quantitative variation in trait often due to effects of more than one gene in pathway = polygenic trait- gets even more complex with diploid cells- finding the genes (loci) responsible for polygenic traits can be difficult- polygenic quantitative trait loci (QTL) or susceptibility loci control many human disorders- correlate molecular differences on chromosomes to occurrence or strength of trait- complex interactions between genes and traits = epistasis - if Cx allele eliminates C?- Ar or Br = moderate arginine- A1Br = less arginine 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.- C2 or ArCx or BrCx or ArBrCx = no arginine - the phenotype of the A and B genes depends on the C gene - C is epistatic (dominates over) A and BWhat if 2 genes are on the same chromosome?:- independent assortment of chromosomes of non-homologous chromosomes - RrYy parent makes 4 different combinations of gametes- crossing over in meiosis 1 recombines parts of homologous chromosomes- synapsis of homologs make tetrad- one chromatid can recombine with another at chiasma- adds more variability to offspringThomas Hunt Morgan (1866-1945):- genetics in Drosophila and the chromosomal theory of inheritanceDo 2 genes on the same chromosome get inherited together?:- fly nomenclature : X+ = normal (wild type, dominant)- X = recessive mutant- b+ = normal wings, vg = vestigial wings (recessive mutant)- if genes "linked" on the same chromosome, show heterozygotes as: b+vg+/bvg homologue pair - non-parental recombinant offspring- crossing over creates non-parental chromosomes and genotypesDistance between "linked" genes on chromosome determines the frequency of crossing over:- crossing over rarely occurs between adjacent genes- crossing commonly occurs between distance genesMapping mutated genes by recombination:- test cross with mutations a + b- % of offspring with non-parental genotype- distance in centimorgans- 50% = random non-parental - looks like unlinked genes- multiple exchangesFine-scale mapping of mutations using crossing over:- What bit of DNA is different in genetic disease?- sequence DNA of everyone with or without disease? Expensive.- correlate presence of disease and mapped, easily deleted, marker mutations = "polymorphisms"- high correlation if low recombination between polymorphism and disease mutation = really close- marker mutations or DNA
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