1. Crossing Over in the Fungus “Sordaria”
AP Biology Lab 3

2. What you need to know!
Important differences between mitosis and meiosis.
How germ cells use meiosis to become gametes
The impact of crossing over on genetic variation
How to map genes using crossing over frequency

3. Sordaria Lifecycle
Sordaria is an alternating diploid (2n) and haploid (n) organism
Alternation of generations
Haploid
Mycelium (n)
Ascospores (n)
Diploid
Sporophyte

4. Sordaria Color Sordaria are either tan or wild type (dark brown)
If grown together they will form hybrid Sordaria
Hybrids are diploid sordaria with both the tan and wild type alleles
Meiosis followed by mitosis create spore pods with 8 spores, called asci
Each spore shows the 1 color it inherited

5. Asci Each spore shows a specific color
The 8 spores form patterns which depend on whether crossing over occured

7. Spore Patterns 4:4 = no Xing over 2:4:2 = Xing over

8. Frequencies and Gene Maps
DNA at the centromere do not exchange during crossing over
The farther from the centromere a gene is, the more likely it will cross over
Calculating crossing over frequency for a gene will determine how far from the centromere the gene is
We use map units as an arbitrary unit for chromosome measurement