What would be the results of a test cross with the F1 flies?

Question

A.  1 brown eye, thin wing veins: 1 red eye, heavy wing veins
B.  1 brown eye, heavy wing veins: 1 red eye, thin wing veins
C.  1 brown eye, thin wing veins: 2 red eye, thin wing veins: 1 red eye, heavy wing veins
D.  1 brown eye, heavy wing veins: 2 red eye, thin wing veins: 1 red eye, thin wing veins

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain?
 
Gather Content
· What do you already know about linked genes and testcrosses?

  Consider Possibilities
· What other information is related to the question? Which information is most useful?
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
 Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
 

Answer 1

A.  1 brown eye, thin wing veins: 1 red eye, heavy wing veins

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses linked genes and testcrosses.
· What type of thinking is required?
        o You need to Analyze the information given, using logic, to dissect the problem and determine the answer.
· What key words does the question contain?
        o A testcross is a cross used to determine the genotype of one of the parents, by looking at the phenotypes that result when crossed to a tester strain.
 
Gather Content
· What do you already know about linked genes and testcrosses?
        o Tightly linked genes segregate together, so you can treat them as a unit.
        o Testcrosses typically use a double homozygous recessive strain, so that any dominant alleles in the other parent are revealed in the progeny.

  Consider Possibilities
· What other information is related to the question? Which information is most useful?
        o Punnett squares are a useful way to determine both genotype and phenotype ratios.
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Since testcrosses typically use a fully recessive homozygous strain, we should assume a homozygous bw hv is crossed to an F1 individual.
        o The F1 are heterozygous bw hv+ / bw+ hv .
        o So the cross is bw hv+ / bw+ hv x bw hv / bw hv.
        o Draw a Punnett square. The tester parent produces only bw hv gametes.
        o Since the genes segregate together, the other parent produces just two kinds of gametes: bw hv+ and bw+ hv.
        o This creates just two combinations of offspring in equal proportion: bw hv+ / bw hv and bw+ hv / bw hv.
        o Their phenotypes are: brown eyes, thin wing veins and red eyes, heavy wing veins.
 Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question required you to Analyze the information given, using logic, to dissect the problem and determine the answer.
        o Did you remember the point of a testcross?
        o Did you recognize that the tester strain should be recessive for all genes?
        o Did you use a Punnett square to help you determine the genotype ratios?
        o Did you correctly match phenotypes to the genotypes?