Chromosome mapping in eukaryotes Flashcards
What’s the recombination rate of genes that are on different chromosomes ?
0,5 (50% chance that an allele from one chromosome is inherited along with an allele from another chromosome –> independent assortment)
Define linkage
When genes are present on the same chromosome, causing them to be inherited together as a unit (provided that they are not separated by crossing over durer meiosis)
True or false : linked genes follow independent assortment
False
The frequency of crossing over between any two loci on a single chromosome is proportional to ___
The distance between them
if 2 genes are very far apart on the same chromosome, what’s their recombination rate ?
0.5 (max : they behave as if they were on separate chromosomes)
Define complete linkage
When 2 genes are so close that they always get inherited together
NO cross-over possible
(F1 individuals will only form parental gametes)
How many types of gametes can be produced when 2 genes are completely linked ?
2 (each of the parental types)
Because both genes are inherited together
What’s the ratio of phenotypes when crossing for 2 genes that are completely linked ?
1:1
How many gametes would be produced when 2 genes are not completely linked ? What’s the genotype ratio ?
4 types of gametes (genes are unliked)
genotypic ratio = 1:2:1
What does it mean when a very small proportion of gametes show a recombinant phenotype ?
Chances of crossing over are very small = the 2 loci are within a short distance
if we have 34,5% of recombinant phenotypes in a sample, what is the distance between the 2 genes observed ?
34,5cM
1 centimorgan is equal to what ?
1% chance of recombinant phenotypes in the next generation
What’s the maximum chance of recombination ? that translates to how many centimorgan ?
50% –> 50cM
True or false : if there is no gene of interest between a double crosse over, it will not be detected
True (the second cross over cancels the recombination that would’ve happened)
How can we calculate the probability of a double cross over (DCO) happening ?
Using the product law ( product of the 2 individuals probabilities for each single cross over)
True or false : expected frequency of double cross-over gametes is always much higher than that of either single cross-over gametes
False, it’s always much lower
Complete : we need a large number of offsprings to detect ___
DCOs (double cross-overs)
What’s interference ?
Interference explains why the observed frequency of DCOs is often lower than the expected frequency of DCOs.
Interference : inhibition of further crossover events by a crossover event in a nearby region (think of the shape the chromosome takes to do a cross over –> takes space)
autrement dit: a cross over can be inhibited by a previous cross over
Interference ranges from -1 to +1. How can we calculate by how much interference decreases the number of DCOs ?
I = 1 - (DCOobserved/DCOexpected) x 100
