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Quizzes > High School Quizzes > Science

Practice Quiz: Incomplete Dominance & Codominance

Hone skills with engaging genetics practice problems

Difficulty: Moderate
Grade: Grade 10
Study OutcomesCheat Sheet
Paper art depicting the dynamic Double Dose Dominance quiz for high school students.

Which term describes a situation where the heterozygote exhibits a blend of both traits?
Complete Dominance
Incomplete Dominance
Codominance
Recessive Expression
Incomplete dominance is characterized by a heterozygote showing a blended or intermediate phenotype. This distinguishes it from complete dominance, where one allele masks the other.
What is codominance?
Allele expression is based on the environment
Heterozygote shows a mixture of traits
One allele completely masks the other allele
Both alleles are fully expressed simultaneously
Codominance occurs when both alleles in a heterozygote are fully and distinctly expressed. Unlike incomplete dominance, there is no blending of the traits.
In incomplete dominance, the phenotype of heterozygotes is usually:
Identical to one of the homozygotes
Completely different from either homozygote
A random mixture of both traits
An intermediate blend between the two homozygotes
The intermediate appearance of heterozygotes is the hallmark of incomplete dominance. This blending distinguishes it from situations where one allele completely masks the other.
Which of the following statements about codominance is correct?
The dominant allele suppresses the recessive allele
Heterozygotes display a diluted phenotype
Only one allele is expressed in heterozygotes
Both alleles in a gene pair are fully expressed in heterozygotes
In codominance, both alleles are expressed independently and visibly. There is no blending, which differentiates it from incomplete dominance.
Which example best illustrates incomplete dominance?
A black and white pattern in a cow
Red and white snapdragons producing pink flowers
Brown eye color masking blue eye color
Human blood type AB where both A and B antigens are expressed
The red and white snapdragon cross that yields pink flowers is the classic example of incomplete dominance. The heterozygote exhibits a phenotype that is intermediate between the two homozygotes.
In a classic cross of two snapdragons with pink flowers (resulting from incomplete dominance, genotype Rw), what is the expected phenotypic ratio in their offspring?
1 pink : 1 white
1 red : 2 pink : 1 white
3 red : 1 white
1 red : 1 pink
Crossing two heterozygous snapdragons (Rw x Rw) results in a 1:2:1 phenotypic ratio. This is typical of incomplete dominance where the heterozygote shows an intermediate phenotype.
In codominance, when two alleles are present, the phenotype generally:
Shows characteristics of both alleles without blending
Shows only the dominant allele
Exhibits an intermediate phenotype
Displays only the recessive allele's trait
Codominance results in the full and separate expression of both alleles in the heterozygote. There is no blending of traits, and each allele's contribution can be clearly observed.
In human blood types, if a person inherits an A allele from one parent and a B allele from the other, the resulting blood type is:
O
B
A
AB
The A and B alleles are codominant, so when both are present, they are expressed simultaneously. This results in the AB blood type, where both antigens appear on red blood cells.
In snapdragons with incomplete dominance, if a flower is pink, its genotype is:
WW
RR
Either RR or WW
RW
A pink flower in snapdragons, where red is dominant and white is recessive in an incomplete dominance system, is the result of a heterozygous genotype (RW). This intermediate genotype produces the blended phenotype.
In a cross between two heterozygous organisms with codominant alleles, what is the typical phenotypic ratio?
1:2:1
3:1
2:1
1:1
When two heterozygotes for a codominant trait are crossed, the resulting genotypes appear in a 1:2:1 ratio. This ratio is directly reflected in the phenotype because both alleles are fully expressed.
Which pattern of inheritance is characterized by neither allele being fully dominant over the other, resulting in a phenotype that is a blend?
Codominance
Complete Dominance
Multiple Allelism
Incomplete Dominance
Incomplete dominance is defined by the production of a phenotype that is intermediate to both homozygous forms. This blending occurs because neither allele completely masks the other.
When analyzing a Punnett square for a trait exhibiting codominance, what observation differentiates it from an incomplete dominance pattern?
The heterozygote phenotype in codominance shows distinct, simultaneous expression of both traits
The heterozygote phenotype shows a mix of traits in both cases
Codominance produces a uniform phenotype
Incomplete dominance always results in a 3:1 ratio
The key difference lies in the phenotype of the heterozygote. In codominance, both alleles are expressed distinctly without blending, whereas in incomplete dominance the heterozygote exhibits an intermediate phenotype.
In a scenario of flower color inheritance via incomplete dominance, crossing two pink-flowered plants (Rw) yields which of the following genotypes?
Only RR or WW
Only RW
RR, RW, WW
Any mix where one allele is dominant
Crossing two heterozygous plants (Rw x Rw) yields three genotypes: RR, RW, and WW. This 1:2:1 ratio is typical of incomplete dominance inheritance.
Which of the following best describes the genetic mechanism in codominance?
A dominant allele prevents the expression of the recessive allele
Alleles interact to create a completely new trait
One allele is only partially expressed in the presence of a dominant allele
Two different alleles are both observably expressed in a heterozygote
In codominance, each allele in a heterozygote is fully expressed, resulting in both traits being visible simultaneously. This situation contrasts with complete dominance where one allele masks the other.
In human genetics, which trait is a common example of codominance?
Blood type AB
Hair type
Ear lobe attachment
Eye color
The AB blood type is a classic example of codominance, where both A and B alleles are expressed. This results in the simultaneous presence of both antigens on red blood cells.
In a dihybrid cross involving two traits that both exhibit incomplete dominance, what is the expected overall phenotypic ratio?
3:3:3:3
1:2:1:2:4:2:1:2:1
1:1:1:1
9:3:3:1
Each trait with incomplete dominance yields a 1:2:1 ratio. When two such traits are inherited independently, their phenotypic ratios multiply to produce a 1:2:1:2:4:2:1:2:1 ratio.
Consider a plant species where flower color exhibits incomplete dominance (red and white produce pink in heterozygotes) and seed coat pattern exhibits codominance (alleles 'C' and 'P' are both expressed in heterozygotes). If two plants heterozygous for seed coat pattern (CP) are crossed, what is the expected genotypic and phenotypic ratio for the seed coat pattern?
1:1 ratio; half show both patterns
1:2:1 ratio; heterozygotes show both patterns
All offspring show a blend of patterns
3:1 ratio; heterozygotes are not distinct
In a codominant system, crossing two heterozygotes (CP x CP) yields a 1:2:1 ratio. The heterozygous individuals distinctly express both alleles, confirming codominance.
In a pedigree analysis involving a trait exhibited through incomplete dominance, an individual displays an intermediate phenotype. Which of the following parental genotypes is most likely responsible?
One parent is heterozygous and the other is homozygous dominant
One parent is homozygous recessive and the other is heterozygous
Both parents are homozygous for opposite traits
Both parents are heterozygous
An intermediate phenotype in incomplete dominance occurs only in heterozygotes. When both parents are heterozygous, there is a significant chance of producing heterozygous offspring.
Which experimental approach would best help distinguish between incomplete dominance and codominance for a trait?
Observing if heterozygotes show a blended phenotype or distinct expressions of both alleles
Analyzing a single generation without crossing
Using environmental stress tests
Measuring gene expression levels in homozygotes only
The defining difference between incomplete dominance and codominance lies in the heterozygote phenotype. By examining whether the heterozygotes show a blended appearance or distinct traits, one can distinguish between the two patterns.
In a laboratory experiment, a researcher observes that a heterozygous individual exhibits both phenotypic traits in distinct areas of tissue. Which genetic inheritance pattern does this observation most likely indicate?
Codominance
Epistasis
Incomplete Dominance
Complete Dominance
When a heterozygote displays both traits in different tissue regions, it is a strong indication of codominance. This pattern ensures that both alleles contribute visibly to the phenotype without blending.
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Study Outcomes

  1. Analyze phenotypic ratios resulting from incomplete dominance and codominance crosses.
  2. Apply genetic principles to predict outcomes in various inheritance scenarios.
  3. Interpret allele interactions to differentiate between incomplete dominance and codominance.
  4. Evaluate test problems to identify conceptual strengths and areas for improvement.
  5. Develop strategies for solving complex inheritance challenges.

Incomplete & Codominance Review Cheat Sheet

  1. Blended Traits in Incomplete Dominance - In incomplete dominance, the heterozygote shows a mix of both parental traits, like juicy pink snapdragon blooms from red and white parents. It's like mixing paint - red and white swirl into a whole new shade! Pearson Biology Guide
  2. Full Expression in Codominance - Codominance lets both alleles shine equally, so you get a roan cow sporting vivid red and white patches at the same time. No blending here; each trait pops like spots on dice! Biology Corner Worksheet
  3. Ratios in Incomplete Dominance - For incomplete dominance crosses you'll often see a 1:2:1 genotypic and phenotypic ratio, meaning one parent color, two blended offspring, and one of the other parent color. Practicing these ratios makes predicting flower colors as easy as counting petals. Biology Notes Online
  4. Ratios in Codominance - Codominance also follows a 1:2:1 ratio, but the heterozygotes show both traits fully - think of two flavors in one scoop! Spotting this pattern helps you nail those Punnett square predictions. Biology Notes Online
  5. Punnett Square Practice - Sharpen your genetics skills by filling out Punnett squares for both incomplete dominance and codominance scenarios. With a little practice, you'll forecast offspring traits faster than a fortune teller! Pearson Exam Prep
  6. Blood Types: A Codominance Example - Human blood types A and B alleles combine in AB individuals, showing codominance with both markers on red blood cells. It's a real-life demo of how two versions can live together in harmony! Pearson Biology Guide
  7. Non‑Mendelian Inheritance - Incomplete dominance and codominance break the classic Mendel rules, giving you more than just dominant or recessive outcomes. Embrace these exceptions - they reveal the rich tapestry of genetic possibilities! Good Science Education
  8. Memory Mnemonics - Use catchy phrases like "Incomplete blends, co‑both shine" to keep the difference clear in your brain. A little rhyme goes a long way when exam time zooms around! Biology Notes Online
  9. Real‑World Case Studies - Peek at snapdragon petals for incomplete dominance and roan cattle for codominance to see these patterns in action. Observing nature's genetics lab makes learning feel like a fun safari! Biology Corner Worksheet
  10. Interactive Flashcards - Quiz yourself with online flashcards and interactive games to reinforce these concepts and track your progress. Turn study time into play time for maximum retention! Pearson Flashcards
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