Virtual FlyLab Experiments, Set III
Working in groups of four assigned in discussion, analyze
the following traits using the
Virtual FlyLab. For each of these
crosses you will be given three traits to analyze at a time.
In addition to determining the inheritance pattern of each
trait individually you need to explain the inheritance
patterns that occur when all mutations are involved in the
same cross (a trihybrid cross). In particular, be sure to
determine the distance between genes on the same chromosome
and the order and any interference if all three of them
should be on the same chromosome. There is no crossing over
in male Drosophila so you have to be very careful about how
you design your crosses if you want to map the distance
between the genes. Don't forget to use the chi-square test
to test any hypotheses that you propose and to give
phenotypic and genotypic diagrams of all relevant crosses
with results. These problems are very difficult, especially
problem 3, and you will work in groups of three to four
students assigned in class and turn in a joint report.
Problems 1 and 2 are worth five points and problem 3 is
worth 15 points, your results are due in your discussion
section, the week of March 5th. There is an updated
scoring rubric for problems 1 and 2
and another one for problem 3.
- The easiest way to do this is to first design a
female fly with all three mutant traits and then cross
this fly with a wild type male.
- Any mutant traits that are present in the F1
females are dominant
- Traits that appear in the males but not the
females are X-linked recessive.
- Lethal traits will have a 1:1 ratio in both males
- If only some of the traits are X-linked use dihybrid
crosses to map the linked genes as in FlyLab 2.
- If all of the traits are either X-linked or autosomal
then cross the trihybrid F1 female with a male fly
homozygous for the recessive traits (design this fly).
Examine the F2 results for evidence of linkage.
- If none of the traits are linked you will see a
1:1:1:1:1:1:1:1 ratio of the eight different phenotype
- If two of the traits are linked there will be two
groups of numbers, one larger than the other. Half of
the phenotype combinations (4) will have the large
numbers, these four combinations contain the parental
configuration for the two linked genes, and the other
half will have the small numbers and are the
- determine which gene is not linked to the other
two (if you're confused, try some dihybrid crosses
to check for the linked genes)
- add all of the recombinants and divide by the
total progeny to get the map distance
- If all three genes are linked then you will get
four different pairs of numbers
- the largest pair should be the parental
- the smallest pair is the double recombinants,
use this to determine which gene is in the middle
- the other two pairs are the single recombinants
between the middle gene and each flanking gene, use
these numbers plus the double recombinants to get
the map distances
- check for interference by calculating an
expected number of double recombinants from the two
flanking distances and compare this to the actual
number of double recombinants
1. Investigate the spineless bristle, dumpy wing and
brown eye traits (5 pts).
2. Investigate the white eye, tan body and crossveinless
wing traits (5 pts.).
3. Black body is located near the middle of chromosme 2.
In Virtual Fly II and III you encountered five other genes
located on chromosome 2. Determine which genes are on
chromsome 2 and the linkage map of all the chromosome 2
genes (15 pts.). Include in your report only crosses used to
determine the map, you can use dihybrids or trihybrids
(trihybrids will be much faster). Also report any
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Last Update: Monday, September 4, 2000