Name:________________________________________
chromosome

Drosophilab Gene Linkage

In this activity, you will continue your exploration of Drosophila inheritance using the program: Drosophilab. These tasks specifically examine cases where alleles are located on the same chromosomes, linkage groups.

Task 6A - Show how linked genes are inherited byoffspring if they are in the cis position

Create a cross using the parent flies labeled Task6.  The parents have the genotypes shown below.

Parent 1: AaBb ←heterozygous, dominant alleles on same chromosomes,  wild-type
Parent 2: aabb ←homozygous, recessive, mutant,  purple eyes, vestigial Wings

1. Create a Punnett square to show the "expected" results of the cross above.

 

 

 

2. Cross the flies using the simulator and count the resulting offspring. Create a table to show your results below.

  Red Eyes,
+ Wings
Red Eyes,
Vg Wings
Purple Eyes,
+ Wings
Purple eyes,
Vg wings
Number (out of 20) observed        
Number (out of 20) expected        

3. Were you results as expected? Explain why you have some flies with unexpected phenotypes.

 

Task 6B- Show how linked genes are inherited by offspring if they are in the trans position

Create a cross using the parent flies labeled Task6.  The parents have the genotypes shown below.

Parent 1: AaBb ←heterozygous, dominant alleles on opposite chromosomes,  wild-type
Parent 2: aabb ←homozygous, recessive, mutant,  purple eyes, vestigial Wings

chromosome

4. Create a Punnett square to show the "expected" results of the cross above.

 

 

5. Create an F1 generation with 20 offspring and record data.  

  Red Eyes,
+ Wings
Red Eyes,
Vg Wings
Purple Eyes,
+ Wings
Purple eyes,
Vg wings
Number (out of 20) observed        
Number (out of 20) expected        

6.  Again, you probably have flies that do not match any of the expected types.  This is due to the fact that alleles on chromosomes can switch position during prophase 1 of meiosis.   Show a diagram of how your alleles in Task 6B could have switched position, changing the outcome of the cross.

 

 

7.  Determine the frequency of cross-over, this is the percentage of the time the alleles switch places, as evidence by offspring you observe that do not have the expected phenotype.  In task 6, any offspring that had two recessive alleles aabb or two dominant alleles AABB signifies a crossover event.  Calculate the percent.  

Percent Cross-Over = _______                 (this is also the distance they are apart in map units)          

8. Go to "TOOLS" in drosophilab and open the chromosome map.

What is the location of the vg allele? ___________ What is the location of the pr allele? ________

How far apart are they in map units based on the chromosome map? ____________

fruit fliesTask 7 - Create Your Own Cross

Go to the chromosome editor and create a male fly with sepia eyes and striped body. Create a female fly that is heterozygous for both traits. You will need to choose whether your alleles are in the trans or cis alignment.

9. Show a Punnett of your cross. Are your alleles in the cis or trans alignment?

 

 

10. Create a data table to show the actual (observed) offspring of this cross.

 

 

 

11. What percent of the time did you observe crossing over? How far apart are the sepia and striped body alleles based on this percentage?

 

 

12. How far apart are the alleles based on known information (from the chromosome map)?