If you crossed flies heterozygous for the Cy allele, what phenotypes would you find in the adult F1 generation?

Question

  Let Cy = curly wings and Cy+ = wild type. In Drosophila, the Cy allele behaves as a dominant mutation that produces curly wings in the heterozygous condition (Cy/Cy+), but also behaves as a recessive lethal mutation. Flies homozygous for the Cy allele die before reaching adulthood.

A.  both wild type and curly wings
B.  wild type only
C.  curly wings only
D.  None because all the F1 flies would die before reaching adulthood.

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 dominant and recessive alleles?

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.  both wild type and curly wings

Clarify Question
· What is the key concept addressed by the question?
        o This question asks about a complex example of one allele that is both recessive and dominant, for different traits.
· What type of thinking is required?
        o This question requires you to Analyze the information to predict an outcome.
· What key words does the question contain?
        o Cy is the abbreviation for the Curly gene. The mutant allele is both recessive – trait exhibited only in the homozygote – and dominant – trait exhibited in the heterozygote. It is recessive for lethality – that is, when homozygous the flies do not survive to adulthood. It is dominant for wing shape. Heterozygotes have curly wings.

Gather Content
· What do you already know about dominant and recessive alleles?
        o You know that dominant alleles are exhibited in the heterozygote, and recessive alleles are exhibited only in the homozygote. Perhaps you did not know that one allele can be both recessive and dominant, for different traits!
        o There are other examples of genes that can be both recessive and dominant. One is the mutation for Manx cats. When heterozygous, they have missing tails. But when homozygous, kittens die in utero.

Consider Possibilities
· What other information is related to the question? Which information is most useful?
        o Don’t let the complexity throw you. Simply write out the cross: Cy / Cy+ x Cy / Cy+
        o Now, you may be able to do this in your head. If not, what approach could you use to see all the categories of offspring?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Try drawing a Punnett square. The gametes are Cy and Cy+ on the top and the side.
        o The combinations in the offspring are thus Cy / Cy (dead), Cy / Cy+ (curly wings, alive), Cy+ / Cy (curly wings, alive), and Cy+ / Cy+ (straight wings, alive).
        o So the two phenotypes seen in adults are curly wings and wild type (straight wings).

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 Writing down the cross is helpful with questions like these. Even better, draw the Punnett square.Q