Topic 4: One-Gene-One-Enzyme

Question 1

Genotype vs phenotype

Answer 1

G: genes and alleles of those genes an individual carries
P: physical expression of the genotype

Question 2

What is forward genetics

Answer 2

Knowing a phenotype, making random mutations, screening for phenotypic change, identifying gene underlying phenotype

Question 3

Genes function by encoding…

Answer 3

enzymes

Question 4

Almost all metabolic pathways are

Answer 4

multistep processes

Question 5

Each step in metabolic pathways are

Answer 5

controlled by different enzymes (thus diff genes)

Question 6

What did Beadle and Tatum study

Answer 6

Metabolism in Neurospora crassa, identified mutants in biochemical pathways for the aa

Question 7

Characteristics of Neurospora

Answer 7

Grow in lab as haploid and diploid
Grow asexually through mitosis (budding)
Makes ascospores
Has a and alpha mating types
Has sexual cycle (meiosis and cell fusion)

Question 8

The one gene, one enzyme hypothesis:

Answer 8

Genes function by encoding enzymes, and each gene encodes a separate enzyme

Question 9

What is an auxotroph

Answer 9

Organisms that will proliferate only when the medium is supplemented with a specific substance not required by the WT organisms

Question 10

What is a phototroph

Answer 10

Organism that will proliferate on minimal media (WT)

Question 11

What is minimal media

Answer 11

Medium only containing inorganic salts, a carbon source and water

Question 12

Slide 10

Answer 12

Beadle and Tatum experiment

Question 13

Explain how auxotrophic mutations can be isolated/identified

Answer 13

Cause mutations to org
Move a cell to complete medium x4
Transfer to minimal media
Whichever does not grow on MM, move to media + aa, whichever it grows on is the aa that’s pathway is broken

Question 14

What is the order of the intermediates in a pathway

Answer 14

First intermediate will have the most (-)
Last intermediate will have the most (+)/least (-)

Question 15

What is the order of the mutants/enzymes

Answer 15

Most (+) is the first
Most (-) is the last

Question 16

Updated hypothesis? For euk?

Answer 16

One-gene-one-polypeptide (enzyme made up of multiple polypeptides)
Euk: one-gene-one or a few-polypeptides

Question 17

What can genetic/mutant screening be used for

Answer 17

Dissect the genetic components of a phenotype of interest (discover which genes are responsible for what)

Question 18

What is a complementation test

Answer 18

Determine whether mutations are at the same locus or at different loci

Question 19

Homozygous genes

Answer 19

Have two copies of the same allele at gene of interest e.g. AA

Question 20

Heterozygous gene

Answer 20

Have different alleles at gene of interest e.g. Aa

Question 21

Dominant allele

Answer 21

Determines the expressed phenotype if present

Question 22

Recessive allele

Answer 22

Only determines the phenotype in homozygous state (aa)

Question 23

How are complementation tests run

Answer 23

Cross parents homozygous for different mutations; offspring are heterozygous (Aa tells us A is dominant)

Question 24

Allelic mutations

Answer 24

Occur at the same locus

Question 25

Offspring when mutations are allelic…

Answer 25

Heterozygous offspring have only mutant alleles
Exhibit a mutant phenotype

Question 26

If mutations occur at different loci, offspring…

Answer 26

Heterozygous offspring inherit a mutant allele and a wildtype allele
Exhibit wildtype phenotype

Question 27

What is haplosufficient

Answer 27

One wildtype allele is enough to get WT phenotype

Question 28

Slides 23/24

Answer 28

Complementation test