Complete dominance is when one allele fully masks the other in a heterozygous plant, so the phenotype shows only the dominant trait. In Intro to Botany, it shows up in Mendelian crosses like pea flower color.
Complete dominance in Intro to Botany is the inheritance pattern where one allele fully determines the phenotype in a heterozygous individual. If a plant has one dominant allele and one recessive allele, the visible trait looks like the dominant trait, not a blend of the two.
That makes complete dominance a genotype-to-phenotype rule. The genotype is the allele pair, such as Aa, but the phenotype is what you can observe, such as purple flowers instead of white ones. In this pattern, the recessive allele is still present in the plant’s DNA, it just does not show up in the visible trait when the dominant allele is there.
Mendel’s pea plant crosses are the classic example. If purple flower color is dominant over white, then a heterozygous plant with one purple allele and one white allele will still have purple flowers. If you cross two heterozygotes, Aa x Aa, you usually get a phenotypic ratio of 3:1 in the offspring, with three showing the dominant trait and one showing the recessive trait.
A useful detail in botany is that complete dominance is about the trait being studied, not about the allele being somehow stronger in every way. One gene can show complete dominance for flower color, but the same kind of dominance pattern might not apply to another trait in the same plant. That is why botany labs often ask you to track one trait at a time and compare observed offspring ratios to expected Mendelian ratios.
This pattern also gives you a clean way to predict inheritance in crosses. If you know the parents’ genotypes, you can use a Punnett square to work out likely offspring genotypes and phenotypes. The dominant allele appears in the phenotype whenever it is present, while the recessive phenotype only appears when both alleles are recessive, such as aa.
Complete dominance is one of the first genetics patterns you use when working with plant traits in Intro to Botany. It gives you the basic logic for moving from allele combinations to visible traits, which is exactly what you do in Mendelian genetics problems.
It also sets up the vocabulary you need for later topics like plant breeding, inherited variation, and trait prediction. When a lab asks you to compare offspring outcomes from a cross, you need to know whether the trait should follow a simple dominant-recessive pattern or something more complicated. Complete dominance is the simplest case, so it becomes the reference point for spotting when a trait does not fit that pattern.
In plant examples, this concept also helps you read results correctly. If a heterozygous plant looks fully dominant, you cannot tell its hidden recessive allele just by looking at it. That matters when you are interpreting crosses, calculating expected ratios, or explaining why a trait can skip a generation and show up again later.
Keep studying Intro to Botany Unit 3
Visual cheatsheet
view galleryallele
Complete dominance only makes sense when you are tracking alleles, the different versions of a gene. A plant’s phenotype depends on which alleles it inherited from its parents, and complete dominance describes what happens when one of those alleles masks the other in the visible trait. You need allele language to read crosses and predict offspring outcomes.
phenotype
The whole point of complete dominance is the phenotype, or the trait you can observe. In a heterozygous plant, the phenotype shows the dominant version of the trait even though the recessive allele is still there. This is why botany problems often ask you to connect what is in the genotype to what you can actually see.
genotype
Genotype tells you the allele combination, while complete dominance tells you how that combination shows up outwardly. A plant can have the same phenotype as a homozygous dominant plant even if its genotype is heterozygous. That gap between genotype and phenotype is a big reason why genetics problems require careful notation.
f2 generation
Complete dominance is easy to spot in the F2 generation of a monohybrid cross, especially after crossing two heterozygous plants. That is where the classic 3:1 phenotype ratio shows up if the trait follows Mendel’s pattern. Botany labs often use the F2 generation to check whether observed offspring fit that expectation.
A quiz question may give you a plant cross and ask for the expected phenotype of the offspring. Your job is to identify whether the trait follows complete dominance, then use the parent genotypes to predict which offspring show the dominant trait and which show the recessive one. If the cross is Aa x Aa, you should recognize the 3:1 phenotype ratio and know that the recessive trait only appears in the homozygous recessive plants.
You may also see a data table or a Punnett square in a lab worksheet and need to explain why a heterozygous plant looks like the dominant parent. That is a direct complete dominance question, even if the assignment uses flowers, seed shape, or another plant trait instead of the phrase itself.
Complete dominance is not a blend. In incomplete dominance, the heterozygote has an intermediate phenotype, like red and white parents producing pink offspring. In complete dominance, the heterozygote looks just like the dominant homozygote, so you do not see an in-between trait.
Complete dominance means one allele fully masks the other in a heterozygous plant.
The visible trait, or phenotype, matches the dominant allele when both dominant and recessive alleles are present.
A heterozygous cross often produces a 3:1 phenotypic ratio in the F2 generation.
The recessive allele is still in the genotype even when it does not show in the phenotype.
This pattern is the classic Mendelian model you use before moving on to more complicated inheritance patterns.
Complete dominance is when one allele fully masks another allele in a heterozygous plant, so only the dominant trait appears. In Intro to Botany, this is the basic Mendelian pattern used to predict visible traits like flower color in pea plants.
In complete dominance, the heterozygote looks like the dominant homozygote, so there is no blended trait. In incomplete dominance, the heterozygote has an intermediate phenotype, which is why the offspring can look like a mix of the two parents.
A heterozygous cross usually gives a 3:1 phenotypic ratio if the trait shows complete dominance. That means three offspring show the dominant trait and one shows the recessive trait. The genotype ratio is different, so do not mix those up.
Yes. In complete dominance, the recessive allele is still present in the genotype, it just does not show in the phenotype when the dominant allele is also there. That is why a trait can seem to disappear and then show up again in later offspring.