43. In general, offspring of barn swallows have tail lengths very similar to their parents. However, if the offspring are removed from their nests while young and transplanted to nests that have parents of significantly different tail lengths, these birds tend to grow tail lengths similar to their "foster" parent types. What explains this result?
Answer: B
Tail length in barn swallows appears to be influenced by both genes and the environment.
The observation that barn swallow offspring can develop tail lengths similar to their foster parents indicates that their growth is affected by environmental factors in addition to genetic inheritance.
A) Tail length in barn swallows follows a genetic pattern of incomplete dominance.
This option is incorrect because incomplete dominance refers to a genetic scenario where the phenotype of heterozygotes is intermediate between the phenotypes of the homozygotes. The evidence presented suggests that environmental factors, rather than a simple genetic interplay, play a significant role in tail length development in these birds.
B) Tail length in barn swallows appears to be influenced by both genes and the environment.
This option is correct as it encapsulates the findings that barn swallow offspring raised by foster parents with different tail lengths tend to mimic those lengths. This indicates that environmental influences, such as the presence of different parental traits, can affect phenotypic expression alongside genetic predispositions.
C) Tail length is a phenotypic trait that follows patterns of Mendelian inheritance.
While tail length could be considered a phenotypic trait, this option does not accurately describe the influence of environmental factors demonstrated in the experiment. Mendelian inheritance alone does not account for the significant environmental impact observed in the offspring's tail length resulting from being raised by different parents.
D) Tail length is not influenced by genotype in barn swallows.
This statement is incorrect as it completely disregards the genetic contribution to tail length. The offspring's similarity to their biological parents indicates that genotype does have a role; however, the environmental factor introduced by foster parenting also significantly affects the outcome.
Conclusion
The correct answer, B, highlights the dual influence of genetic and environmental factors on the tail length of barn swallows. Other options fail to account for the environmental effect observed when offspring are raised by foster parents, which leads to a phenotypic outcome that diverges from purely genetic expectations. This illustrates the complex interplay between genes and environment in determining physical traits.