Dominant — Science definition
Expressed in the heterozygote under a specified complete-dominance model; not necessarily common or beneficial.
Where it is taught
- Mendelian Genetics — DNA, Inheritance & Gene Expression, Life Science: Biology, Grade 10
In use
Under complete dominance, the heterozygote has the modeled dominant phenotype.
Mendelian Genetics
Questions using dominant
Problem 1
If B (brown) is dominant over b (white), an organism with genotype Bb will have which phenotype?
- A blend of brown and white
- It cannot be determined
- Brown
- White
Answer and explanation
Brown
One dominant B is enough to produce the brown phenotype, so Bb is brown.
Problem 2
In a cross between two Bb parents (B dominant), what percent of the offspring are expected to show the recessive phenotype?
Answer and explanation
25 %
Bb x Bb gives BB, Bb, Bb, bb — 1 of the 4 boxes (25%) is bb, the recessive phenotype.
Problem 3
In a hypothetical complete-dominance model, an organism with dominant phenotype could be BB or Bb. Explain a model test cross and the limit of a small sample.
Answer and explanation
Cross with bb under the model. Any bb offspring implies the tested parent supplied b. All dominant offspring in a small sample do not prove BB because Bb can produce such a sample by chance.
Problem 4
Two Tt parents (T dominant). The probability that two of their offspring in a row are both tt equals 1 out of what number?
Answer and explanation
16 (1 out of this many)
Each tt has probability 1/4; multiplying independent events, 1/4 x 1/4 = 1/16, so 1 out of 16.