4/29 Flashcards
(23 cards)
when two genes are very far, what happens to the accuracy of the % recombination/ map distances?
it becomes less accurate, the observed number of recombinant offspring will underestimate the actual distance between the genes
why does map distance get more inaccurate as genes are further apart
the likelihood of multiple crossovers increases and even numbers of crossovers won’t be counted as recombinations
if three recombination events occur, how many are counted?
only 1 is actually counted, the other is viewed as a double crossover which returns the linkage back to its parent state
at 50% recombination, what happens to the proportions of the phenotypes?
it appears like independent assortment and there are equal amounts of each phenotype
how can genes be mapped?
it can be calculated by calculating the map distances between nearby linked genes that will have less instances of recombination
when genes are too far apart, why can their map distances cannot be calculated
they may act like thye are independently assorting or have an underestimation of cross over events
why are trihybrid crosses helpful
they help detect double cross over events as the middle gene will swap places and the two surrounding genes maintain the same linkage
true or false, double cross over events are frequent
false they are rare
how do you calculate the amount of offspring with a single crossover recombination?
E=np
n= total number offspring
p= probability of recombination (% recombination/ map distance)
how do you calculate the probability of a double cross over event
(probability of single cross over event 1)(probability of single cross over event 2)
if we see a lesser amount of double cross over events than we expect, what does this mean
this indicates positive interference
if we see more amounts of double cross over events than we expect, what does this mean
this indicates negative interference
what is positive interference
when the observed value is less than the expected value, the first crossover decreases the probability of a second
how do you calculate interference?
I=1-C where C= # of observed DCO/# of expected DCO
if you have an interference of 60% what does this mean
this means 60% ox the expected cross overs did not occur
what is negative nterference
it is where the amount of observed DCOs is greater than the expected DCO
what is mitotic recombination
it is recombination that occurs in mitosis and is considered a mutation
how does a heterozygote phenotype work
two proposed theories:
50% of the protein from the dominant allele is enough or the gene is upregulated so more protein is expressed to compensate for the loss of function
what is a gain of function dominant allele
the mutated gene produces a protein that gains a new function
at is a dominant negative allele
it is where the protein encoded by the mutant gene acts antagonistically to the normal protein. In a heterozygote, the mutant protein counteracts the normal protein and changes the phenotype
what is haploinsufficiency
a single copy within a heterozygote is not enough to make the wildtype protein and two copies are required
During a mapping experiment the number of observed double crossover events will always equal the number of expected crossover events. true or false
false
