Mendelian Genetics

Question 1

WT yeast is a prototroph

Answer 1

-can generate its own food from basic chemicals
-grow yeast on minimal, well-defined media and yeast will make all of the amino acids and proteins it needs
-yeast can also grow on inexpensive media made up of ground up yeast cells and has additional amino acids/sugar sources

Question 2

YPD media

Answer 2

-yeast extract, peptone, and dextrose
-standard media that is inexpensive and made up of ground up yeast cells and has additional amino acids

Question 3

uracil biosynthesis pathway

Answer 3

yeast uses this to make UTP

Question 4

auxotrophs

Answer 4

-mutant yeast that requires molecule to be added in media
-auxotroph will survive only if the essential molecule is provided in the media

Question 5

screen for URA- mutants

Answer 5

-haploid yeast- mutation will likely be recessive and you have a slim chance of hitting both alleles during the screen
-plate yeast in YPD media after mutagenesis since it has everything you need to grow, including the mutants you need
-for replica plating, use minimal media + amino acids WITHOUT URA to select for colonies that were unable to grow due to lack of URA

Question 6

FOA selection for URA- mutants

Answer 6

-FOA- an acid is converted to the toxic compound by the URA3 gene product, so those without the ura-3gene will live
-use haploid yeast again then mutagenzie the yeast with EMS
-spread out on minimal media + amino acids/bases + FOA
-colonies that grow are FOA resistant –> mutants in the ura-3 gene
-can also make a master plate as a control to make sure the FOA selection is working
-survivors have the mutants you are looking for

Question 7

screen vs selection

Answer 7

-screen- unbiased approach to looking at all possible mutations –> fast way to get lots of alleles of specific pools of genes that can mutate through that phenotype
-selection- limited to the ones that you know will act on a certain change in media but this can be advantageous if you already know a gene that you’re interested in works with FOA then you save time
-screen you look at all mutations and wild type together and let them grow then change the media to see the phenotypes of interest (forward genetics)
-selection is more narrowed approach since you have an idea of the specific mutations –> more efficient and cost effective

Question 8

null (amorph)

Answer 8

-complete loss of function = null allele
-same effect as removing the entire gene

null allele/null allele = null allele/Df = Df/Df

Question 9

hypomorph

Answer 9

-partial loss of function
-ts allele, less stable protein, promoter down mutation

null/null < hypomorph/null < hypomorph/hypomorph

Question 10

hypermorph

Answer 10

-increased WT function
-more active protein, more stable protein, promoter up

hypermorph/+;Dp(+) < hypermorph/+ < hypermorph/null <= +/+

Question 11

antimorph (poisonous)

Answer 11

-reduced function- dominant
-interferes with WT allele

antimorph/null < antimorph/+ < antimorph/+;Dp(+)

Question 12

neomorph

Answer 12

-new function
-a mutant receptor that responds to new ligand
-least informative mutation

neomorph/null = neomorph/+ = neomorph/+;Dp(+)

Question 13

how do you find our if two mutants are in the same gene?

Answer 13

cross them with each other and perform complementation test

Question 14

complementation groups

Answer 14

alleles that are in the same gene and therefore do not complement each other

Question 15

complementation test

Answer 15

-look for minuses in the table and those alleles are typically in the same group
-if one of the alleles has a minus with everyone, it is considered Dominant and therefore cannot be easily used for complementation testing

Question 16

what point do you stop doing the complementation screen?

Answer 16

when you reach saturation, which is when you keep getting alleles in the same gene

Question 17

what are exceptions to the complementation test?

Answer 17

-essential genes
-small genes
-duplicated or redundant genes

Question 18

how can two mutations be in the same gene?

Answer 18

intragenic complementation occurs when two mutations in the same gene complement each other –> this can occur through different domains of the protein, reduced amount of improper interactions caused by a mutation, or stabilization where two changes in the protein structure allow for interaction

Question 19

which types of mutations are dominant?

Answer 19

hypermorph, antimorph, and neomorph

Question 20

which types of mutations are recessive?

Answer 20

amorph and hypomorph