A scientist crosses genes of a pine tree with broad needles (BB) with a pine tree with thin needles (tt). The F, generation of pine trees has a genotypic ratio of 100% Bt. When the scientist looks at the trees, he or she sees only broad needles. Which conclusion can be made about these trees?
A.
The broad needle trait is dominant to the thin needle trait.
B.
To avoid broad needles, the scientist must cross two parent plants other than tt.
C.
To produce thin needles, the scientist must cross two parent plants that are both BB.
D.
The thin needle trait is dominant to the broad needle trait.
The correct answer and Explanation is :
The correct answer is A. The broad needle trait is dominant to the thin needle trait.
Explanation:
In genetics, when analyzing the inheritance of traits, the dominant and recessive nature of alleles determines the observable characteristics. Here’s a step-by-step explanation based on the given scenario:
- Genotypes of Parent Trees:
- The first pine tree has broad needles and its genotype is given as BB. This means both alleles for needle width are dominant for broad needles.
- The second pine tree has thin needles and its genotype is tt, meaning both alleles for needle width are recessive for thin needles.
- F1 Generation Results:
- When these two trees are crossed (BB x tt), all the offspring in the F1 generation have the genotype Bt. This indicates that each F1 tree inherits one dominant allele (B) and one recessive allele (t) for needle width.
- Phenotypic Observation:
- Despite having the genotype Bt, all F1 trees exhibit broad needles. This observation is critical in understanding the dominance relationship between the alleles.
- Understanding Dominance:
- In this case, the presence of the broad needle trait in all F1 offspring suggests that the broad needle allele (B) is dominant over the thin needle allele (t). Therefore, the trait associated with the dominant allele (B) is expressed in the phenotype, regardless of whether the other allele is dominant or recessive.
- Dominance and Recessiveness:
- Since all the F1 plants display broad needles, it implies that the dominant broad needle trait masks the expression of the recessive thin needle trait. If the thin needle trait were dominant, we would expect to see thin needles in the F1 generation.
In conclusion, the broad needle trait being expressed in all F1 generation trees demonstrates that it is dominant over the thin needle trait. Thus, the correct conclusion is that the broad needle trait is dominant to the thin needle trait.