Question: 1. All the genes on a single chromosome are physically linked .
Two genes are genetically linked …
1. All the genes on a single chromosome are physically linked .
Two genes are genetically linked if they segregate together in
meiosis more frequently than they segregate separately. Two
physically linked genes that always segregate together show
complete genetic linkage . Two genes on the same chromosome that
usually but not alway s segregate together are incompletely or
partially linked . How can two genes be physically linked but not
be genetically linked? Explain the phenomenon of incomplete
linkage.
2. A genetic linkage group consists of all loci that are
genetically linked to one another. What is the relationship between
the number of genetic linkage groups and the number of pairs of
homologous chromosomes in an organism?
3. Thomas Hunt Morgan postulated a direct relations hip between
the cytological observation of crossing over in meiosis (with an
apparent physical exchange of segments of homologous chromosomes)
and the genetic evidence for an exchange of alleles between two
homologous chromosomes. Barbara McClintock provi ded the definitive
proof of Morgan’s hypothesis. What was the crucial experiment?
4. The frequency with which random events occur between two
points is a function of the distance between those two points. How
do we use this principle to map genes in eu karyotes?
5. If the frequency of recombinant progeny (the recombination
frequency ) from a cross between one individual heterozygous at two
loci and a second individual homozygous recessive at both of those
loci is less than 50%, the two genes in questi on are genetically
linked. What can we conclude about the genetic and physical linkage
of two genes when the recombination frequency between those two
genes is equal to 50%?
6. Why is crossing over, or recombination, in meiosis a genetic
advantage for a n organism? Why is crossing over an advantage for a
geneticist?
7. Why would one want to construct a genetic map for an
organism? What advantage(s) does having a genetic map provide for
breeders, counselors, and other folks?
