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Quizzes > Science

Phenotype Test Online: Genotype and Phenotype Practice Quiz

Quick, free genotype and phenotype quiz. Instant results and clear explanations.

Editorial: Review CompletedCreated By: Alex RobinsonUpdated Aug 28, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration for genotype phenotype quiz with DNA strands icons and coral background to test genetics knowledge

Use this quiz to connect genotypes with phenotypes, predict traits with Mendelian rules, and spot gaps before a test. If you want more review, try our phenotype quiz for extra trait questions, practice crosses with punnett square practice, or broaden your scope with a molecular genetics quiz.

What term describes the genetic makeup of an organism?
Phenotype
Genome
Genotype
Karyotype
The genotype of an organism refers to its specific set of genes or alleles that it carries. It contrasts with the phenotype, which is the observable expression of those genes. Knowing the genotype is crucial for predicting inheritance patterns. For more details, see .
Which term describes the observable characteristics of an organism?
Genotype
Genome
Phenotype
Allele
The phenotype encompasses all of an organism's observable traits, such as morphology, development, biochemical or physiological properties. These traits result from the interaction of its genotype with the environment. Thus, phenotype is what you can see or measure directly. For more information, visit .
What term is used for having two identical alleles of a gene?
Heterozygous
Hemizygous
Homozygous
Hybrid
An organism is homozygous for a gene when it carries two identical alleles, such as AA or aa. Homozygous individuals will pass on the same allele to their offspring. The counterpart, heterozygous, carries two different alleles (e.g., Aa). Additional details are available at .
According to Mendel's Law of Segregation, what happens to alleles during gamete formation?
They separate so each gamete carries one allele
They duplicate and both copies go into each gamete
They mutate at random
They blend to form intermediate alleles
Mendel's Law of Segregation states that during gamete formation, the two alleles for a trait separate so that each gamete carries only one allele. This ensures offspring inherit one allele from each parent. This principle underlies the predictable ratios seen in Punnett square analyses. See for more.
If T represents the dominant tall allele and t the recessive short allele in pea plants, what phenotype will a Tt plant display?
Varied height in different environments
Tall
Short
Intermediate height
In a classic dominant - recessive relationship, the presence of one dominant allele (T) masks the expression of the recessive allele (t). Therefore, a heterozygote (Tt) will display the dominant phenotype (tall). This behavior is fundamental to Mendel's observations. More information can be found at .
Which genotype notation indicates a heterozygous individual?
Rr
AA
RRRR
rr
A heterozygous genotype consists of two different alleles, for example Rr. Homozygous genotypes would be two identical alleles (AA or rr). The notation helps predict offspring genotypes and phenotypes. More on allele notation is available at .
In a monohybrid cross between two heterozygotes (Aa × Aa), what proportion of the offspring is expected to show the recessive phenotype?
50%
100%
75%
25%
When two heterozygotes (Aa × Aa) are crossed, Punnett square analysis predicts a 1:2:1 genotypic ratio (AA:Aa:aa), and only the aa genotype shows the recessive phenotype. That corresponds to 1 out of 4 or 25%. For details, see .
Which of the following illustrates codominance in genetics?
Red and white snapdragon producing pink flowers
Tall allele masking short allele
Two alleles blending to form an intermediate trait
Blood type AB expressing both A and B antigens
Codominance occurs when both alleles in a heterozygote are fully expressed, as seen in human blood type AB, where both A and B antigens appear on red blood cells. This differs from incomplete dominance, where alleles blend to form an intermediate phenotype. Further examples are discussed at .
What phenotypic ratio is expected in the F2 generation of a dihybrid cross assuming independent assortment?
27:9:9:3
9:3:3:1
1:1:1:1
3:1
A dihybrid cross (AaBb × AaBb) following Mendel's law of independent assortment yields a 9:3:3:1 phenotype ratio in the F2 generation. This ratio corresponds to all combinations of dominant and recessive alleles for two traits. More at .
What is epistasis?
When one gene masks the expression of another
Genes located on the same chromosome
A blend of two alleles in heterozygotes
Expression of multiple traits by one gene
Epistasis occurs when the expression of one gene is affected or completely masked by the presence of one or more modifier genes. Unlike dominance, epistasis involves interactions between different gene loci. Details can be found at .
Which term describes when one gene influences multiple, seemingly unrelated phenotypic traits?
Linkage
Pleiotropy
Polygenic inheritance
Epistasis
Pleiotropy refers to a single gene affecting two or more distinct and seemingly unrelated traits. Classic examples include the Marfan syndrome gene affecting connective tissue in multiple organ systems. Visit for further reading.
What describes polygenic inheritance?
Trait controlled by many genes each with small effect
A single gene with multiple alleles
One gene masking another
Genes located in mitochondria
Polygenic inheritance involves multiple genes contributing additively to a single trait, such as human height or skin color. Each gene may have a small effect, resulting in a continuous distribution of phenotypes. More on this topic at .
How can the environment influence phenotype?
By affecting gene expression and trait development
By altering an organism's genotype directly
Environment has no influence on phenotype
By changing the dominant allele to recessive
Environmental factors such as temperature, nutrition, and light can influence gene expression and thus phenotype without altering the genotype. For example, hydrangea flower color can change based on soil pH. This gene - environment interaction is key to understanding trait variability. See .
Why are X-linked recessive disorders more common in males?
Males have a higher mutation rate
Females inactivate one X chromosome
Males have two X chromosomes
Males only need one copy of the recessive allele
Males have only one X chromosome (XY), so a single recessive allele on the X chromosome will cause the disorder. Females (XX) would require two copies of the recessive allele to express the trait. This pattern explains why conditions like hemophilia are more frequent in males. More at .
An autosomal recessive disorder will appear in offspring only if:
Both parents pass on a recessive allele
The disorder skips two generations
At least one dominant allele is present
One parent carries the allele
Autosomal recessive disorders manifest only when an individual inherits two copies of the recessive allele, one from each carrier parent. Carriers (heterozygotes) typically show no symptoms. This inheritance pattern leads to a 25% risk for affected offspring when both parents are carriers. See .
What is the primary use of the chi-square test in genetics experiments?
To test if observed data fit expected ratios
To map genes on chromosomes
To calculate allele frequencies
To measure gene expression levels
The chi-square test in genetics is used to determine whether observed offspring ratios deviate significantly from expected Mendelian ratios. It compares observed counts to theoretical expectations and provides a p-value. A high p-value suggests data fit the model. Additional reading at .
What does incomplete penetrance mean?
Not all individuals with a genotype show the expected phenotype
Two alleles share expression equally
Gene is located on the mitochondrial genome
Phenotype varies depending on environment
Incomplete penetrance occurs when some individuals carrying a disease-causing genotype do not exhibit the disease phenotype. This can result from modifier genes, environment, or stochastic factors. Understanding penetrance is vital for genetic counseling. See .
A recombination frequency of 10% between two genes indicates they are approximately how many map units apart?
50 map units
100 map units
1 map unit
10 map units
Recombination frequency reflects the physical distance between genes on a chromosome. A 1% recombination frequency equals one map unit (centimorgan). Thus, 10% frequency corresponds to roughly 10 map units. Further explanation at .
What is genetic drift?
Change in allele frequency due to selection pressure
Random fluctuation in allele frequencies in small populations
Mutation creating new alleles
Migration of individuals between populations
Genetic drift refers to random changes in allele frequencies that occur especially in small populations, potentially leading to allele loss or fixation. It differs from natural selection, which is non-random. Drift can reduce genetic variation over time. More at .
In a population at Hardy - Weinberg equilibrium with allele frequencies p = 0.8 and q = 0.2, what proportion of individuals are expected to be homozygous dominant?
0.80
0.64
0.04
0.16
Under Hardy - Weinberg equilibrium, the expected frequency of homozygous dominant individuals is p². With p = 0.8, p² = 0.64 or 64%. This assumes random mating, no selection, mutation, or migration. For more, see .
What does the selection coefficient (s) measure in population genetics?
Mutation rate per locus
Absolute fitness of a genotype
Relative change in allele frequency per generation
Reduction in fitness of a genotype relative to the most fit genotype
The selection coefficient (s) quantifies the reduction in fitness of a particular genotype compared to the genotype with the highest fitness (usually set to 1). It ranges from 0 (no selection) to 1 (complete selection against). This parameter helps predict allele frequency changes. More at .
Which pattern of inheritance describes mitochondrial genes?
Mendelian autosomal inheritance
Strictly maternal inheritance
Y-linked inheritance
Strictly paternal inheritance
Mitochondrial DNA is inherited exclusively from the mother in most species because sperm mitochondria are typically degraded after fertilization. Thus, mitochondrial disorders follow a maternal inheritance pattern. Details at .
What is genomic imprinting?
Random mutation of alleles during gamete formation
Simultaneous expression of both alleles
Expression of all genes on one chromosome
Allele expression depends on parent of origin
Genomic imprinting is an epigenetic phenomenon where the expression of a gene depends on whether it was inherited from the mother or the father. Imprinted genes are silenced by DNA methylation on one allele. This selective expression can lead to parent-specific effects on development. More information at .
Which approach is commonly used to identify quantitative trait loci (QTL) in a crop species?
Chromosomal karyotyping
Linkage mapping using molecular markers
Northern blotting of RNA
Single-gene knockout analysis
Quantitative trait loci are regions of the genome that correlate with variation in a quantitative trait. Linkage mapping with molecular markers across segregating populations helps pinpoint QTL locations. Advanced methods also include genome-wide association studies. For more, see .
In CRISPR-Cas9 gene editing, what component directs Cas9 to the specific DNA sequence to be cut?
Protospacer adjacent motif (PAM)
Cas9 protein alone
Donor DNA template
Single guide RNA (sgRNA)
In the CRISPR-Cas9 system, the single guide RNA (sgRNA) contains a 20-nucleotide sequence complementary to the target DNA and directs Cas9 to that location. The adjacent PAM sequence is required for cutting but does not provide specificity. The sgRNA - Cas9 complex then induces a double-strand break. For details, see .
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Study Outcomes

  1. Understand Key Genetic Concepts -

    After engaging with this genotype and phenotype practice quiz, you will grasp the difference between genotype and phenotype and recognize how alleles contribute to observable traits.

  2. Analyze Allele Combinations -

    Learn to categorize genotypes using Punnett squares and predict phenotypic ratios, reinforcing how genotypes are the outward expression of an allele combination.

  3. Apply Mendelian Principles -

    Use Mendel's laws to solve real-world genetics problems and predict inheritance patterns through our targeted genotype phenotype practice questions.

  4. Interpret Phenotypic Outcomes -

    Develop skills to connect allele combinations to trait expressions and assess the likelihood of specific phenotypes appearing in offspring.

  5. Evaluate Genetic Scenarios -

    Critically assess case studies and practice questions in this genetics quiz online to reinforce your understanding of heredity and variation.

  6. Navigate Online Genetics Quizzes -

    Gain confidence in tackling diverse question formats and enhance your test-taking strategies for future genetics assessments.

Cheat Sheet

  1. Fundamentals of Mendelian Inheritance -

    Review Gregor Mendel's laws - Law of Segregation and Law of Independent Assortment - which explain how alleles segregate and sort independently during gamete formation. A handy mnemonic is "S.I. Test" (Segregation, Independent assortment, Test cross) to recall the key steps. These core principles are essential for any genotype and phenotype practice and are detailed in resources like the University of California's genetics primer.

  2. Punnett Squares for Predicting Ratios -

    Use a Punnett square to visualize allele combinations and calculate expected genotype and phenotype ratios, such as a monohybrid cross (Aa × Aa) yielding 1:2:1 genotypic and 3:1 phenotypic ratios. Label parental gametes on the axes and fill in the grid to predict outcomes in your genotype phenotype practice. This method, endorsed by Khan Academy and other academic sites, sharpens your skills for a genetics quiz online.

  3. Defining Genotype vs Phenotype -

    Remember that genotype refers to the genetic makeup (e.g., AA, Aa, aa) while phenotype is the observable trait influenced by those alleles and environment ("nature vs. nurture"). A simple shorthand is "genotype in the genes, phenotype on the scene." This concept clarifies that genotypes are the outward expression of an allele combination but can be modified by external factors.

  4. Allele Types: Dominant, Recessive, Codominant -

    Classify alleles as dominant (masking), recessive (masked), codominant (both expressed), or incompletely dominant (blended). For example, in blood groups (IA and IB codominant), both traits appear, while in snapdragon flowers, red and white blend to pink (incomplete dominance). Understanding these patterns enriches your genotype and phenotype practice by highlighting real-world genetic diversity.

  5. Beyond Simple Traits: Polygenic and Epistasis -

    Many traits, like skin color or height, are polygenic - controlled by multiple genes - and can show continuous variation; epistasis occurs when one gene affects another's expression. A quick tip: think "poly = many genes, epi = on top of" to distinguish these patterns in your study notes. Mastery of these concepts prepares you for challenging questions in any genetics quiz online.

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