Topic 4: One-Gene-One-Enzyme Flashcards
Genotype vs phenotype
G: genes and alleles of those genes an individual carries
P: physical expression of the genotype
What is forward genetics
Knowing a phenotype, making random mutations, screening for phenotypic change, identifying gene underlying phenotype
Genes function by encoding…
enzymes
Almost all metabolic pathways are
multistep processes
Each step in metabolic pathways are
controlled by different enzymes (thus diff genes)
What did Beadle and Tatum study
Metabolism in Neurospora crassa, identified mutants in biochemical pathways for the aa
Characteristics of Neurospora
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)
The one gene, one enzyme hypothesis:
Genes function by encoding enzymes, and each gene encodes a separate enzyme
What is an auxotroph
Organisms that will proliferate only when the medium is supplemented with a specific substance not required by the WT organisms
What is a phototroph
Organism that will proliferate on minimal media (WT)
What is minimal media
Medium only containing inorganic salts, a carbon source and water
Slide 10
Beadle and Tatum experiment
Explain how auxotrophic mutations can be isolated/identified
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
What is the order of the intermediates in a pathway
First intermediate will have the most (-)
Last intermediate will have the most (+)/least (-)
What is the order of the mutants/enzymes
Most (+) is the first
Most (-) is the last
Updated hypothesis? For euk?
One-gene-one-polypeptide (enzyme made up of multiple polypeptides)
Euk: one-gene-one or a few-polypeptides
What can genetic/mutant screening be used for
Dissect the genetic components of a phenotype of interest (discover which genes are responsible for what)
What is a complementation test
Determine whether mutations are at the same locus or at different loci
Homozygous genes
Have two copies of the same allele at gene of interest e.g. AA
Heterozygous gene
Have different alleles at gene of interest e.g. Aa
Dominant allele
Determines the expressed phenotype if present
Recessive allele
Only determines the phenotype in homozygous state (aa)
How are complementation tests run
Cross parents homozygous for different mutations; offspring are heterozygous (Aa tells us A is dominant)
Allelic mutations
Occur at the same locus
Offspring when mutations are allelic…
Heterozygous offspring have only mutant alleles
Exhibit a mutant phenotype
If mutations occur at different loci, offspring…
Heterozygous offspring inherit a mutant allele and a wildtype allele
Exhibit wildtype phenotype
What is haplosufficient
One wildtype allele is enough to get WT phenotype
Slides 23/24
Complementation test
