5 - genetic analysis Flashcards
what are the benefits of using escherichia coli as a model organism?
– small cell size – 20 min generation time – easy to culture – known genetic code – known mechanisms of DNA replication – spontaneous nature of mutations
most useful for:
antibiotic resistance, pathogen resistance, basic molecular machinery of a cell
what are the benefits of using saccharomyces cerevisiae (budding yeast) as a model organism?
– single celled eukaryote ∴ combines convenience of bacteria with the features of eukaryotes
– easy grown and cultured on plates
– 90 min cell cycle
– used to identify cell cycle genes and mechanisms of recombination
– able to study gene interactions
most useful for:
cell cycle studies, basic eukaryotic cell biochemistry and biology, haploid genetics
what are the benefits of using caenorhabditis elegans (naemotoad) as a model organism?
– has a defined number of cells – transparent ∴ cell fate can be traced – can be frozen – can feed on E.coli and grown on plates – able to study programmed cell death – able to study RNAinterferase – able to study micro RNAs in development
what are the benefits of using drosophila melanogaster (fruit fly) as a model organism?
– easy to obtain – short life cycle (~10 days) – easy to perform crosses – large number of mutants – 70% of cancer genes have drosophila counter parts
most useful for:
developmental biology, balancer chromosomes, maternal effect genes
what are the benefits of using danio rario (zebrafish) as a model organism?
VERTEBRAE MODEL ORGANISM
– transparent embryos and external fertilisation ∴ very easy to induce mutation
– easy to breed
– complete generation in 5-6 months
– can model for some human neuronal diseases
most useful for:
vertebrate development, large mapping populations, easy transgenics
what are the benefits of using mus musculus (mouse) as a model organism?
MAMMALIAN MODEL ORGANISM
– genetic similarity with humans – genome sequences available – able to study genetic basis of skin colour – able to study gene knockouts – able to test carcinogens – model for mammalian development
what are the benefits of using aradiposis thaliana as a model organism?
PLANT MODEL ORGANISM
– complete genome sequence
– small and easy to grow, life cycle ~ 5 weeks
– able to identify developmental genes
– able to study plant physiology and environmental effects
– population genetics
what is the difference between forward and reverse genetic analysis?
forward:
isolate a mutant based on phenotype → identify the genes which carry the mutant
i.e. mapping
reverse:
identify which genes are present via sequencing → find out function of gene
what is EMS and ENU?
how are they used to study genetics?
EMS = induce G:C to A:T transitions ENU = A:T to T:A transitions + G:C to A:T transitions
feed organism with EMS/ENS
analyse phenotypes of M2 generation
– first generation: recessive mutant exists in heterozygote form and will not be visible in phenotype
– second generation: mutant with separate into homozygous recessive state and can be identified
how do you determine if mutant are located in the same gene?
COMPLEMENTATION TEST
mutations are said to be complementary if they are located in different genes
begin by crossing two mutants
if the progeny is heterozygous, the recessive mutations must be located in different genes as the homozygous state is lost
describe how you would test for epistasis between two mutants
EXAMPLE: eye colour in drosophila
WT: dark red eyes
cinnabar mutant: bright red eyes
white mutant: white eyes
Begin with a dihybrid cross (ccWW x CCww) to obtain heterozygotes (CcWw = WT phenotype)
Cross heterozygotes and observe phenotype of F2 generation
Expected = 9:3:3:1 = WT : red : white : light red
Observed = 9:3:4 = WT : red : white
(expect double homozygous to have mixed phenotype but it is white-eyed)
White mutant phenotype masks/dominates cinnabar
∴ white is epistatic to cinnabar
This means the white enzyme/protein must be last in the pathway for eye-colour
describe the additive interaction between mutants.
what is the difference between additive and synergistic interactions?
additive interaction = the effects of the two mutants combine and are both visible in the double mutant phenotype
EXAMPLE: FLOWERING TIME • WT = 17 days • flm mutant = 14 days • maf2 mutant = 15 days • flm + maf2 = 12 days
synergy occurs when the contribution of two mutations to the phenotype of a double mutant exceeds the expectations from the additive effects of the individual mutations
what is a homeotic mutations
homeotic genes regulate the development of anatomical structures
homeotic mutations can disrupt or displace anatomical parts
how can genetic screening be used to identify the function of a mutation?
mutagenise a mutant and look for the effect on the phenotype
enhancer screen: identifies mutations which enhance the phenotype of interest.
suppressor screen: identifies mutations which alleviate/revert the phenotype of interest
new mutants can be:
– second-site (intra-genic, rare)
– interaction (epistatic, synergistic
rewatch leccy on molecular markers and recombination
follow along with example problem