9 Molecular Basis of Gene Interactions Flashcards
Polygenic inheritance - interaction between genes
Genes cooperate in the production of a trait —> formation of molecule complexes / molecular pathways (eg. Cell signalling)
Function of 1 gene can mask / modify function of another cooperating gene (Epistasis) —> protein of 1 gene may stimulate or repress another gene and its protein / Absence of a functional gene often affects the function of another gene and its protein
Epistasis
1 gene can mask / modify function of another cooperating gene
gene that is doing the masking…
Epistatic
masked gene
hypostatic to the other
Epistatic rations may allow a geneticist to determine…
the order of genes in a particulatar pathway
Dominant Epistasis ratio
12:3:1
dominant allele of 1 gene masks the effect of both alleles on the other gene
Complementary gene action ratio
9:7
2 genes needed to produce characteristics (eg. Snapdragon colour)
DIAGRAMS ON ONENOTE
Duplicate gene action ratios
15:1 ratio of phenotypes
double dominant alleles, 2 genes working on same part of pathway
DIAGRAM ON ONENOTE
Dominant suppression Epistasis RATIO
13:3
certain genes can suppress the expression of a gene at a second locus
DIAGRAM ON ONENOTE
Why is the 9:3:3:1 ratio not always seen
Recombination
Recombination during meiosis - what did Morgan observe
Prophase 1
Chias at a mark on site of recombination
Recombination occurs at random positions along the chromosome
Recombination during meiosis - What Morgan Predicted
Genetic recombination - mixing of genes during gametogensis produces gametes with combinations of genes that are different from the combinations received from parents
Genes on non-homologous chromosomes (unlinked) assort independently - as predicted by Mendel
Genes of same chromosome can co-segregate
Cross overs result in recombination between linked genes
The basis of those ratios
Cross over frequency is a function of the distance between 2 loci - the closer the 2 loci the less chance of a cross over event
Odd number of crossovers between 2 loci
recombinant chromosome can be detected
Even number of crossovers between 2 loci
no recombination is detected
Mapping Genes + Recombination
Recombination frequency of 2 genes can tell us how far apart they are on the chromosome, by comparing multiple pairs of genes we shoukd be able to tell the order of genes along the chromosome
Recombination frequency equation
Number of recombinant / number of test cross progeny X 100
Recombination frequency can be used as a measure of distance
genetic distance is measured in units called mu (Map unit)
Eg. cM (centiMorgan)
Example questions on Lecture Slides
What does 40% recombination frequnecy really mean
Cross over occurred in 40% of the population BUT this means that each recombinant chromosome will be present in the population 20% of the time
The maximum Rf is 50, when Rf = 50 genes are unlinked
If recombination occurs 50% of the time there are an equal number of parental and recombinants, so its impossible to know which is which - similar to Punnett square
Therefore Rf >50 is impossible to calculate
How to identify whether genes are on separate chromosomes or far apart on same chromosome
- Identify more genes in the linkage group
SUMMARY AND QUESTIONS
ONENOTE AND LECTURE SLIDES
