The wild-type (normal) fruit fly, Drosophila melanogaster, has straight wings an

Question

The wild-type (normal) fruit fly, Drosophila melanogaster, has straight wings and long bristles Mutant strains have been isolated that have either curled wings of short bristles. The genes representing these two mutant traits are located on separate autosomes. Carefully examine the data from the crosses shown below (The numbers represent the number of progeny) Abbreviations: Str straight wings, Cur-curled wings, Sh=short bristles, Lg=long bristles Parental cross 1. Str Sh x Str Sh 2. Str Lg x Str Lg 3. Cur Lg x Str Sh 4. Str Sh x Str Sh 5. Cur Sh x Str Sh Str Lg 30 120 Str Sh 90 0 Cur Sh 30 0 Cur Lg 10 120 0 0 20 20 60 Based on the results, which of the following statement is correct? The parents of cross 1 are homozygous for both the wing and bristle traits Short bristle is recessive and curled wing is dominant Both short bristle and curled wing are dominant Both short bristle and curled wing are recessive Short bristle is dominant and curled wing is recessive Submit Answer Tries 0/4

Explanation / Answer

Option 1 The parents of cross 1 are homozygous for both wing and bristle traits   (False)

Reason. The progeny of cross 1 has non non parental(Cur,Lg; Str,Lg and Cur,Sh) phenotypes as well. This means the parents are not true breeding and contain alleles for non parental phenotypes as well. They are not homozygous

Option 2. Short bristle is recessive and curled wing is dominant   (False)

Reason. In the cross 1 we can see that two parents with short bristle(Sh) are producing both Short(sh) as well as Long(Lg) bristled offsprings. In other words both parents are non true breeding with respect to their phenotype. Since the trait expressed in a non true breeding parent is the dominant one we can conclude that Short(Sh) bristle is dominant. Also parent exhibit similar pattern with respect to straight wings as well i.e. straight(Str) wing is dominant over curled(Cur)

Option 3. Both short bristle and curled wing are dominant.    (False)

Reason. From earlier statements we know Sh is indeed dominant over Lg. However Cur is recessive while Str is dominant.

Option 4 Both short bristle and curled wing are recessive   (False)

Reason. Only Curled(cur) wing is recessive.

Option 5. Short bristle is dominant and curled wing   (True)

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