Question

A pure-breeding fruit fly with curled wings mates with a pure-breeding fruit fly with normal (straight) wings. The F1 mate with each other to produce an generation that consists of 160 flies with curled wings and 80 with straight wings. What can you infer from this observation?

- Two interacting genes determine wing shape.
- Curled wings is a recessive trait.
- Wing shape is controlled by two co-dominant alleles.
- All of the hybrid F 1 flies had straight wings.
- The dominant curled wing allele is also a recessive lethal.

Answer 1

We can deduce that curled wings is a recessive trait associated with a recessive lethal allele in fruit flies, altering the expected phenotypic ratio to 2:1 instead of 3:1 due to the lethality of the homozygous recessive genotype.

Step-by-step explanation:

From the observation that a mating between F1 fruit flies resulted in 160 offspring with curled wings and 80 with straight wings, we can infer that curled wings is a recessive trait. This is evident from the 2:1 ratio of curled to straight wings in the offspring, which suggests a recessive lethal allele is at play. Since the trait for curled wings appears in two-thirds of the flies, it suggests that the allele for curled wings is lethal when homozygous recessive (individuals with two copies of the allele do not survive), and only those that are heterozygous for the trait (carrying one dominant and one recessive allele) show the curled wing phenotype.

This follows a typical Mendelian inheritance pattern where a recessive lethal allele affects survival, thus changing the expected 3:1 dominant-to-recessive phenotypic ratio to a 2:1 ratio due to the lethality of the homozygous recessive genotype.