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AP Biology Sordaria Lab Meiosis

AP Biology Sordaria Lab Meiosis. Sordaria Life Cycle. Species of microscopic fungus. Commonly found in the feces of herbivores Haploid for most of the life cycle & exists in a mass called the mycelium ( “ body ” of fungus)

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AP Biology Sordaria Lab Meiosis

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  1. AP BiologySordaria LabMeiosis

  2. Sordaria Life Cycle • Species of microscopic fungus. • Commonly found in the feces of herbivores • Haploid for most of the life cycle & exists in a mass called the mycelium (“body” of fungus) • Ascospores (haploid)  mycelium  forms fungal filaments (hyphae)  2 hyphae fuse (diploid zygote)  meiosis  ascospores • Spore color gene: black (wild type) or tan (mutant) Wild type Mutant

  3. Sardoria Perithecium and Asci Perithecium- fruiting body of the fungus Ascus- sexual spore-bearing cell, surrounds ascospores Ascospores- spores (gametes), 8 ascospores/ascus perithecium ruptured perithecium ascus Perithecium ruptures and ascus with ascospores are released

  4. Ascospore Arrangement • Arrangement of ascospores in ascus can be used to determine if crossing over has occurred during meiosis. • Ratios can be used to determine the gene’s distance from the centromere and each other • no crossing over • 4:4 arrangement • crossing over • 2:2:2:2 arrangment • 2:4:2 arrangement

  5. Ascospore Arrangement Patterns

  6. No Crossing Over 4 x 4

  7. Crossing Over 2, 2, 2, 2 2,4,2

  8. Crossing Over and Gene Mapping Crossover events allow us to approximate distances between genes and map chromosomes • Theory states that the farther two genes are from one another (or from the centromere), the more likely they will be crossed over to a non-sister chromatid during meiosis • Conversely, if two genes are close to one another, the likelihood is low that they will crossover, and they will end up on the same chromosome

  9. Hypothesis Statements H0: Genes are NOT linked on the same chromosome (no evidence of crossover exists) Ha: Genes exist together on the same chromosome (evidence of crossover exists)

  10. Counting Recombinant Asci Count all the recombinant asci on the picture cards. - count only complete asci (ones with 8 ascospores) Do not count ascospores that are all tan or all black. Record your results in your table. Published results: 27 map units How to identify the asci non- recombinant recombinant

  11. Calculating Color Gene to Centromere Distance 1. Count # NoncrossoverAsci # Crossover Asci Total # Asci 2. Calculate recombination frequency # crossovers/ total # 3. Corrected value: % recombination ÷ 2 Mitosis event after meiosis  2 asci formed 4. This is the map distance from gene to centromere

  12. Sardoria Table

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