Examkin

Question

Difficulty: MediumBasic Genetics Terminology and Concepts

A geneticist crosses two heterozygous tall pea plants (TtTt). In the resulting offspring, some plants display the dwarf trait even though both parent plants were tall. Which genetic principle best explains why the dwarf trait was masked in the parent generation?

  1. The allele for dwarfness is recessive and masked by the dominant allele for tallnessAnswer
  2. B
    The allele for dwarfness exhibits codominance with the allele for tallness
  3. C
    Stem height in pea plants is governed strictly by continuous variation
  4. D
    The dwarf trait is an acquired somatic characteristic produced by environmental factors

Answer

The allele for dwarfness is recessive and masked by the dominant allele for tallness in the heterozygous parent generation.
The option stating that the allele for dwarfness is recessive and masked by the dominant allele for tallness is correct because in heterozygous organisms (TtTt), the dominant allele determines the phenotype, keeping the recessive allele hidden until inherited in a homozygous recessive state (tttt).

Step-by-Step Solution

1
Identify the parental genotypes and phenotypes
Both parent plants have the heterozygous genotype TtTt and display the tall phenotype.
Since both parents are tall but carry the dwarf allele (tt), the tall allele (TT) must be dominant.
2
Analyze the expression of alleles in the heterozygous state
In TtTt individuals, the recessive allele (tt) is masked phenotypically by the dominant allele (TT).
By definition of dominance and recessiveness in basic genetics, a recessive allele is only expressed when two copies are present (tttt).
3
Relate to the appearance of dwarf offspring in the F1 generation
Segregation of alleles produces tttt offspring with a 25% probability, revealing the masked recessive trait.
The reappearance of dwarf plants proves that the dwarf allele was present but masked in the heterozygous parents.

Key Concept

Dominant and Recessive Alleles in Heterozygous Organisms
Estimated Time:1m 0s
Rate this question

Topics

Basic Genetics Terminology and Concepts

More questions from this topic