Lab 5: Fungal Genetics

Question 1

Why are fungi good for genetic research?

Answer 1

1) they have a haploid life cycle, phenotype reflects genotype.
2) they also have a diploid cycle if one wanted to determine allelic relationships
3) can be grown on chemical medium- growth or no growth on certain medium can depict biochemical mutants.
4) one spore can produce a lot of progeny

Question 2

What two species did we work with in the lab? Name some of their characteristics

Answer 2

1) Saccharomyces cerevisiae: unicellular eukaryote. Heterophallic because different organisms have different sexes, and it reproduces asxually by budding. USED FOR GENE MAPPING TETRAD ANALYSIS
2) Sordaria Fimicola: filamentus, homothallic (one organisms contains both male and female parts, allowingit to go through sexual reproduction with itself) produces linear asci. Gene mapping of centrosomes

Question 3

What plates can the yeast grow on

Answer 3

YMM: minimal medium. only has carbon, nitrogen and some vitamins. Only yeast strains that can make their own proteins and nutrients can grow on this. YMM cannot support biochemically mutated forms of yeast.

YPD: nutritionally complete medium, has glucose, yeast extract and peptone. Can support all yeast strains.

Question 4

Outline the life cycle of yeast

Answer 4

haploid opposite mating types each form an elongated schmoo, that fuse together to form a mating figure. a diploid organism buds off from the figure. The diploid can be transferred to a sporulation medium (YSM) and it will undergo MEIOSIS to form a haploid tetrad in ascus. these haploid spores can be streaked and tested for their nutritional requirements/mating type analyzed. If mating cells were complimentary in their nutritional requirements, the resulting diploid can grow on a plate that the parents couldn’t.

Question 5

What were the two mating types strains tested in this lab (for a monohybrid trait)

Answer 5

alpha ade 2- cannot make adenine, needs adenine, can make leucine
a leu 2- cannot make leucine, needs leucine, can make adenine

mating types under go conjugation to form spores that can make adenine (from a) and can make leucine (from alpha), thus it can grow on YMM

Progeny: alpha/a

Question 6

Why do you need to compare original strains on YPD plate?

Answer 6

as a control. All should grow on YPD plate, including parents, because YPD is nutritionally complete.v

Question 7

How would you make the diploid yeast strain undergo meiosis to form haploid spores?

Answer 7

you need YSM medium (very minimal nutrients). YSM is insufficient in nutrients, ascospores are more resistant to harsh environements than the diploid stage, yeast can survive in dominant ascospore stage on YSM.

Question 8

How can you tell is yeast ascus is parental ditype? non parental ditype? tetratype?

Answer 8

parental ditype: when all four spores in the ascus have the same genotype as the haploid parent

non-parental ditype: when all four spores in the ascus have haploid recombinant genotypes

tetratype tetrad: if two spores have parental, and 2 spores have recombinant.

Question 9

How can you tell if the 2 traits are linked? Unlinked?

Answer 9

if PD asci > NPS asci = linked

PD=NPD= unlinked, normal segregation has occurred.

Question 10

If you crossed two haploid parents for 2 traits with the genotype: f+.g x f.g+, what would the parental genotypes of the spores be? what would the non parental genotypes be?

Answer 10

parental genotypes: f+.g, f.g+

recombinant genotypes: f+.g+, f.g.

Question 11

What is the percent recombination equation?

Answer 11

[(NPD+1/2TT)/ Total tetrads] x 100.

Question 12

if the parents are a ade2ser1+ and alpha ade2+ser1, which genotypes are parental? recombinant?

Answer 12

parental: ade2ser1+, ade2+ser1
recombinant: ade2ser1, ade 2+ser 1+

Question 13

What is special about meiosis in Sordaria that allows centromere mapping to be done in this organism but not in Saccharomyces?

Answer 13

unlike yeast cells and other organisms where the planes of division in meiosis 1 and 2 are perpendicular causing their spindles to overlap, sordaria produce ordered tetrads for easy analysis because the plans of division in meiosis 1 and 2 are parallel, with no overlapping spindles, allowing the spores to have a linear arrangement. asci in sordaria allow for gene centromere mapping.

Question 14

How does sordaria store its asci?

Answer 14

in a perithecium

Question 15

How can you tell if a tetrad is FDL/Parental? SDS/Recom?

Answer 15

FDS: 4 black spores and 4 white spores in a row
SDS: any combination of black and white spores

Question 16

What does FDS indicate? what does SDS indicate?

Answer 16

FDS; no crossing over has occurred. the two alleles segregated from each other during meiosis one

SDS; crossing over has occurred. the two alleles segregated from each other during meiosis two.

Question 17

In sordaria, how can you determine the gene-centromere distance?

Answer 17

% recomb= gene centromere distance= [(0.5SDS)/Total FDS and SDS tetrads] x 100