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) 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

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

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

Ascospore Arrangement Patterns

No Crossing Over 4 x 4

Crossing Over 2, 2, 2, 2 2,4,2

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

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)

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

Calculating Color Gene to Centromere Distance 1. Count # Noncrossover Asci # 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

Sample Data (tan x wild cross) Sardoria Table Sample Data (tan x wild cross) Number of Asci not Showing Crossover 4:4 Asci 2:2:2:2 Or 2:4:2 Total Counted % % Showing Crossover/2 (only ½ of ascospores are a result of crossing over, other half are just a mitotic copy) Gene to Centromere Distance (map units) 157 168 325 168/325=0.52 0.52/2=.26 .26x100=26% 27 m.u. (published data)