Gene Linkage Flashcards
Linked Genes
On the same chromosome
Why don’t linked genes assort independently?
Linked genes are exceptions to the law of independent assortment because two genes are located on the same chromosome, but this is generally mitigated when chromosomes cross over.
When a dihybrid is testcrossed, how are the parental vs. recombinant classes of progeny immediately identified?
The #. A majority of the offspring will typically demonstrate the parental recombination. There will be much fewer recombinant offspring.
Distinguish between the trans and cis arrangement of alleles in a dihybrid.
Trans: one mutant allele and one wild type allele on the same chromosome Ex: Ab/aB
Cis: both mutant alleles and both wild type alleles on the same chromosome Ex: AB/ab
Why do genes that are 50 map units or more apart appear unlinked?
As map distance increases, recombination of alleles is more likely. At 50 map units, there is 50% recombination which means that the alleles act independently of one another - predicted ratios are seen here. (Ex: 1-1-1-1 for AaBb x aabb)
How does map distance relate to recombination frequency?
1 map unit = 1% recombination.
How is map distance between two genes determined?
(# of recombinants/total) x 100
From a two-point testcross that produces 200 offspring, 20
of the offspring are recombinant and 180 are parental types.
What is the map distance between the two genes?
10 map units
If two loci are 12 map units apart, and an AB/ab (cis)
individual is testcrossed:
a. there will be 12% Ab/ab individuals.
b. there will be 88% Ab/ab individuals.
c. there will be 6% aB/ab individuals.
d. there will be 44% Ab/ab individuals.
c. there will be 6% aB/ab individuals.
