Teaching Genetic Linkage and Recombination through Mapping with Molecular Markers
Lisa McDonnell and Jennifer Klenz
IN-CLASS HANDOUT B
In your teams of six, answer these questions to teach one another about your F2 predictions.
F1 self-fertilized  Generate an F2 population
1. Which genotypes and banding patterns are parental and
recombinant if you are analyzing the drought sensitive plants
only? (think about the gametes that combined to make each
plant)
2. Which genotypes and banding patterns are parental and
recombinant if you are analyzing the drought
only?
tolerant plants
3. For each of the three populations below, indicate if you can detect linkage and determine the map distance
between the DR and G loci, and if so the map distance, by examining the banding patterns:
Detect linkage & determine map distance? Explain why or why not:
Yes or No
The F2 drought tolerant plants
only
The F2 drought sensitive
plants only
The entire F2 population
Challenge: If a gene and marker are so tightly linked that there is almost no recombination between the loci,
what phenotypes (drought tolerant/sensitive) and banding patterns will you observe in the F2?
Teaching Genetic Linkage and Recombination through Mapping with Molecular Markers
Lisa McDonnell and Jennifer Klenz
HANDOUT B ANSWERS
FOR INSTRUCTORS
1. Which genotypes and banding patterns are parental and
recombinant if you are analyzing the drought sensitive plants
only? (think about the gametes that combined to make each
plant)
200/400 pattern could be
parental/parental if two parental gamete types combine:
DRS G400 /DRT G200 or
recombinant/recombinant if two recombinant gamete
types combine: DRT G400 / DRS G200
400/400 pattern could be:
parental/parental: DRS G400 / DRS G400, or
parental/recombinant: DRS G400/ DRT G400,
200/200 could be:
parental/recombinant: DRT G200/ DRS G200, or
recombinant/recombinant DRS G200/ DRS G200
2. Which genotypes and banding patterns are parental and recombinant if you are analyzing the drought
tolerant plants only?
Parental/recombinant: DRT G200/ DRT G400
Recombinant/recombinant: DRT G400/ DRT G400
Parental/parental: DRT G200/ DRT G200
Teaching Genetic Linkage and Recombination through Mapping with Molecular Markers
Lisa McDonnell and Jennifer Klenz
4. For each of the three populations below, indicate if you can detect linkage and determine the map distance
between the DR and G loci, and if so the map distance, by examining the banding patterns:
Detect linkage & determine map distance? Explain why or why not:
Yes or No
Yes
For every band on the gel we know if it is
The F2 drought tolerant plants
recombinant or parental, therefore we can calculate
only
the frequency of recombinants (which tells us about
linkage and map distance).
No
Each banding pattern can be parental or
The F2 drought sensitive
recombinant. If we cannot tell the difference
plants only
between parental and recombinant we cannot
calculate the frequency of recombinants and
therefore linkage/map distance cannot be
determined.
The entire F2 population
No
If we cannot determine which bands are parental
and recombinant in the drought sensitive plants, we
cannot accurately determine linkage or map
distance.
Challenge: If a gene and marker are so tightly linked that there is almost no recombination between the loci,
what phenotypes (drought tolerant/sensitive) and banding patterns will you observe in the F2?
No recombination means that all the gamete types from the F1 will be the parental types: DRT G200 and DRS G400,
so in the F2 we expect:
Frist gamete /second gamete
¼
DRT G200
/ DRT G200
drought tolerant
T 200
¼
DR G
/ DRS G400
drought sensitive
S 400
T 200
¼
DR G
/ DR G
drought sensitive
¼
DRS G400
/ DRS G400
drought sensitive
 3:1 drought sensitive: drought tolerant
¼ drought tolerant homozygous 200/200, ½ drought tolerant 200/400, ½ not tolerant homozygous 400/400