Lecture 7 - Linkage & recombination Flashcards
Why does Mendel’s law of independent assortment not apply when the genes are linked?
as Mendel’s law of independent assortment only holds true for genes that are NOT carried close together on the same chromosomes
Why might the ratios of progeny not be what we expected?
the genes might be linked
What type of progeny might you expect if the genes are linked?
parental genotypes in equal proportion
What is the formula for recombination frequency?
RF = recombinants/total meiotic products x 100%
What is RF roughly proportional to?
the distance between the 2 loci
Does the chance of a recombination event occur increase or decrease the closer the genes are?
decrease
What determines the strength of linkage?
the distance between the genes
What would the % of recombination be if 2 loci were right next to each other?
0% - RF (recombination frequency)
What would the % of recombination be if 2 loci were on separate chromosomes?
50% recombinant & 50% parental - 50% RF
What is the maximum possible RF?
50%
What does a low RF% suggest?
relatively low % suggests that the loci are close together
Does the ratio of alleles change in a tetrad?
NO - the ratio of alleles stay the same
What tetrad do 2 linked genes create?
parental ditype
What is parental ditype?
all 4 products of meiosis are the same as one of the parent
What tetrad do 2 unliked genes (independent assortment) create?
50% of the time - all parental genotype - PARENTAL DITYPE
50% of the time - all non-parental genotypes - NON-PARENTAL DITYPE
What does a single crossover between 2 loosely linked genes give?
a tetratype
What is the tetrad tetratype?
2 parental & 2 non-parental genotypes
If there are lots more parental ditype than non-parental ditype, are the genes linked?
yes - we can conclude that the genes are linked
If you see about the same number of parental ditype and non-parental ditype, are the genes linked?
no - we can conclude that the genes are unlinked
How many samples do you need to complete a chi-squared?
5
What is a recombinant?
any segregate that is different from both parents
