Key Points. Linkage.
Why is it that sister chromatid exchange, as long as it is reciprocal, does not lead to
new combinations of alleles at linked loci?
If there was loss or gain of chromatin with each crossover event, do you think that
crossing over would have evolved as such a potent source of genetic variation?
What are the consequences (if any) – in terms of segregation and in terms of
independent assortment – of the random alignment of non-homologous
chromosomes on the Metaphase I “plate”?
Consider the following data from a testcross in a tropical flower.
Purple
non-aromatic
42
Purple
aromatic
8
White nonaromatic
6
White
aromatic
44
Which phenotypes are non-parental?
What is the distance (expressed as % recombination) between the color and aroma
loci?
If you converted the % recombination to cM, would the value be larger or smaller?
Is recombination at meiosis a source of new alleles, a source of new combinations of
alleles at linked loci, or both?
How can you determine if the association of two traits in inheritance is due to
linkage or pleiotropy?
If you discover that a negative association between two traits is due to pleiotropy
(e.g. good flavor and disease susceptibility), what option(s) do you have to develop a
variety of your favorite plant that has good flavor and is disease resistant?
You read that a species is 2n = 28 but when you make a linkage map you get 22
linkage groups. What are two possible explanations?
Define the following terms, as they relate to linkage:
Chiasma
Sister chromatid
Non-sister chromatid
Cis/coupling
Trans/repulsion
Explain how two loci on the same chromosome can show independent assortment.
The examples of linkage analysis have all involved doubled haploid or test cross
examples. Is it possible to do linkage analysis with an F2?
Why are molecular markers more popular for linkage map construction than naked
eye polymorphisms?
Differentiate between homology, homoeology, synteny, and orthology.