Monohybrid Cross – Definition, Steps, Examples, Practice

What is a Monohybrid Cross?

A monohybrid cross is a genetic cross between individuals who differ in only one trait or allele set. It is the study of inheritance patterns for a single trait, typically with a focus on a single gene with two opposing alleles.

In a monohybrid cross, two heterozygous (having two distinct alleles) individuals for a specific trait are crossed. One allele is inherited from each parent, and the progeny are observed to determine the inheritance and expression of the trait.

To illustrate a monohybrid cross, consider a simplified example of pea plant flower hue. Consider a flower-color gene with two alleles: “A” for purple flowers and “a” for white flowers. In this instance, a monohybrid cross would entail crossing two plants with the flower color phenotype “Aa” (heterozygous).

The F1 generation will inherit one allele from each parent when these two plants are crossed. As the “A” allele is dominant over the “a” allele, the possible genotypes of the F1 generation will be “AA” (homozygous dominant) and “Aa” (heterozygous), while the phenotype will be purple flowers.

Based on the principles of Mendelian genetics, if the F1 generation plants are allowed to self-fertilize or are crossed with other plants of the same genotype, the resulting F2 generation will manifest a specific ratio of phenotypes and genotypes. In this situation, the phenotypic ratio will be 3:1, with three plants displaying purple flowers (AA or Aa) and one plant displaying white flowers (aa).

By analyzing the patterns of inheritance in monohybrid crosses, scientists can determine the underlying genetic principles involved in the transmission of traits from generation to generation. Monohybrid crosses are a fundamental tool for the study of genetics and can be used to predict the likelihood that certain traits will arise in future generations.

Monohybrid Cross Definition

A monohybrid cross is a genetic cross between two individuals that differ in only one trait or one set of alleles. It involves the study of inheritance patterns for a single characteristic, typically focusing on a single gene with two contrasting alleles. The purpose of a monohybrid cross is to observe how the trait is inherited and expressed in the offspring. By analyzing the patterns of inheritance in monohybrid crosses, scientists can understand how traits are passed from one generation to the next and determine the underlying genetic principles involved.

Steps of Monohybrid Cross

The steps involved in a monohybrid cross are as follows:

1. Identify the traits: Determine the specific trait or characteristic of interest that you want to study. For example, consider flower color in pea plants.
2. Define the alleles: Identify the two alleles that control the trait. Assign symbols to represent each allele. In our example, let’s use “A” to represent the dominant allele for purple flowers and “a” for the recessive allele for white flowers.
3. Determine the parental generation: Select two individuals with different genotypes for the trait. For a monohybrid cross, choose parents that are heterozygous for the trait, meaning they have one dominant allele and one recessive allele. In our example, the parents would have the genotype “Aa.”
4. Write the parental genotypes: Represent the genotypes of the parents using the allele symbols identified in step 2. In our example, write the genotypes of the parents as “Aa” and “Aa.”
5. Determine possible gametes: Identify the possible types of gametes (sperm and egg cells) each parent can produce based on their genotype. In our example, both parents can produce two types of gametes: “A” and “a.”
6. Create a Punnett square: Construct a Punnett square, which is a grid used to predict the possible genotypes and phenotypes of the offspring. Place the possible gametes of one parent along the top row of the grid and the possible gametes of the other parent along the left column.
7. Fill in the Punnett square: Combine the gametes by matching each type of gamete from one parent with each type from the other parent. Fill in the squares of the Punnett square with the resulting combinations. This represents the possible genotypes of the offspring.
8. Determine the genotypic and phenotypic ratios: Count the number of squares showing each genotype in the Punnett square. This will give you the genotypic ratio. Then, determine the phenotypes corresponding to each genotype and calculate the phenotypic ratio.
9. Analyze the results: Interpret the genotypic and phenotypic ratios obtained from the Punnett square to understand how the trait is inherited and expressed in the offspring.

These steps help scientists predict the outcomes of a monohybrid cross and understand the principles of inheritance for a single characteristic controlled by a single gene.

Monohybrid Cross example

Gregor Mendel’s Peas Experiemnt

• Gregor Mendel, the renowned Austrian monk and scientist, conducted groundbreaking experiments with pea plants in the mid-19th century, unraveling the mysteries of inheritance and laying the foundation for modern genetics. His study of pea plants became known as “Gregor Mendel’s Pea Experiment.”
• Mendel’s objective was to investigate the inheritance patterns of specific traits within pea plants. One such trait was the length of the plants, which exhibited variation between tall and short varieties. Through meticulous observations and controlled breeding experiments, Mendel sought to determine the underlying principles of inheritance.
• To conduct his experiments, Mendel selectively bred pea plants that possessed distinct characteristics. He focused on two distinct varieties: tall plants and short plants. He discovered that the trait for plant height was governed by the interaction of specific genetic factors, or alleles.
• Mendel denoted the alleles responsible for plant height with the letters “T” and “t.” The homozygous tall plants were represented by the genotype “TT,” indicating that both alleles were identical and dominant for height. Conversely, the homozygous short plants were represented by the genotype “tt,” signifying the absence of the dominant allele.
• To determine the mode of inheritance, Mendel performed a monohybrid cross by mating a tall plant (TT) with a short plant (tt). The resulting offspring, known as the F1 generation, possessed a heterozygous genotype, denoted as “Tt.” These hybrids displayed the phenotype of tall plants, indicating that the trait for tallness was dominant over shortness.
• In subsequent experiments, Mendel took the F1 generation plants and allowed them to self-pollinate. This produced the F2 generation, where he observed a consistent ratio of traits. Approximately 75% of the plants displayed the tall phenotype, while the remaining 25% exhibited the short phenotype.
• Mendel’s analysis of the F2 generation led him to propose the existence of discrete units of inheritance, which he called “factors” or “genes.” He also discovered that these genes could be present in different forms, known as alleles, and that the inheritance of traits followed predictable patterns.
• Gregor Mendel’s pea experiments marked a significant turning point in our understanding of heredity. By carefully studying the inheritance of specific traits in pea plants, he unveiled the principles of dominance and recessiveness, as well as the concept of discrete hereditary units. His pioneering work paved the way for future generations of geneticists and laid the groundwork for the field of modern genetics.

Huntington’s Disease

• Huntington’s disease, a hereditary neurological disorder, serves as an example of monohybrid cross in the study of genetics. This condition is caused by a genetic mutation in the Huntingtin gene, leading to the development of the disease over time.
• Researchers have conducted extensive studies to unravel the genotypic conditions associated with Huntington’s disease. Through careful analysis of affected individuals and their offspring, scientists have made significant discoveries regarding the inheritance pattern of this disorder.
• In the context of monohybrid cross, a homozygous dominant gene is paired with a homozygous recessive gene. In the case of Huntington’s disease, individuals affected by the disorder are considered homozygous dominant for the disease-causing allele, denoted as HD.
• When an affected individual with the homozygous dominant genotype (HD/HD) mates with an individual who carries the homozygous recessive genotype (hd/hd), studies have revealed a consistent pattern in the offspring. Regardless of the other parent’s genotype, all the children born from such a cross inherit the dominant allele for Huntington’s disease (HD).
• This discovery suggests that the dominant allele, HD, is responsible for the onset of Huntington’s disease. Consequently, all the offspring of an affected individual carrying the homozygous dominant genotype (HD/HD) are expected to inherit the disease.
• It is crucial to note that the inheritance of Huntington’s disease is not solely limited to the monohybrid cross. The disease is also influenced by other genetic factors and the phenomenon of genetic anticipation, where symptoms tend to appear at an earlier age in subsequent generations.
• By studying Huntington’s disease as an example of monohybrid cross, researchers have gained valuable insights into the genetic mechanisms underlying the condition. This understanding contributes to improved diagnosis, genetic counseling, and potential avenues for future treatment and prevention strategies for Huntington’s disease.

Confirming Dominant Traits

• In the field of genetics, confirming dominant traits plays a crucial role in understanding the inheritance patterns of specific characteristics. While monohybrid crosses provide initial insights into the dominance of alleles, it is often necessary to conduct heterozygous crosses to solidify these findings and confirm the nature of a trait.
• The methodology employed in this second phase closely resembles the approach pioneered by Gregor Mendel in his experiments with peas. To illustrate this process, let’s consider the example of stem length. Imagine scientists breeding two parents with long stems, each possessing the genotype Ll. By crossing these individuals, the resulting offspring have a diverse range of genotypes.
• In an ideal scenario, one out of every four offspring will inherit the genotype ll, indicating the presence of a recessive allele and resulting in a short stem phenotype. The remaining three out of four offspring, with either the genotype LL or Ll, will display the long stem phenotype associated with the dominant allele.
• When analyzing the data from this second iteration, scientists observe that the occurrence of long stems is more frequent than that of short stems. Based on this observation, a reasonable conclusion can be drawn: long stems are indeed a dominant trait in this particular context.
• This confirmation of dominant traits through heterozygous crosses enables scientists to gain a deeper understanding of the genetic mechanisms underlying specific characteristics. By establishing the dominance or recessiveness of certain traits, researchers can further unravel the complexities of inheritance and contribute to the wider body of knowledge in the field of genetics.
• In conclusion, while monohybrid crosses provide a preliminary understanding of allele dominance, the process of confirming dominant traits through heterozygous crosses is essential in solidifying these findings. Through meticulous observation and analysis of offspring phenotypes, scientists can ascertain the prevalence of specific traits and expand our understanding of genetic inheritance patterns.

Other Examples

Example 1: Flower color in pea plants

Trait: Flower color

Alleles: “A” for purple flowers (dominant) and “a” for white flowers (recessive)

Parental generation: Parent 1: Homozygous dominant (AA) for flower color Parent 2: Homozygous recessive (aa) for flower color

Punnett square:

A A

a Aa Aa

a Aa Aa

Resulting offspring (F1 generation): All offspring will have the genotype Aa and the phenotype of purple flowers because the dominant allele A masks the recessive allele a.

Example 2: Seed shape in pea plants

Trait: Seed shape

Alleles: “R” for round seeds (dominant) and “r” for wrinkled seeds (recessive)

Parental generation: Parent 1: Homozygous dominant (RR) for seed shape Parent 2: Homozygous recessive (rr) for seed shape

Punnett square:

R R

r Rr Rr

r Rr Rr

Resulting offspring (F1 generation): All offspring will have the genotype Rr and the phenotype of round seeds because the dominant allele R masks the recessive allele r.

Example 3: Hairline shape in humans

Trait: Hairline shape

Alleles: “W” for widow’s peak (dominant) and “w” for straight hairline (recessive)

Parental generation: Parent 1: Heterozygous (Ww) for hairline shape Parent 2: Heterozygous (Ww) for hairline shape

Punnett square:

W W

W WW Ww

w Ww ww

Resulting offspring (F1 generation): The genotypic ratio of the offspring will be 1 WW : 2 Ww : 1 ww, while the phenotypic ratio will be 3 individuals with a widow’s peak (WW or Ww) : 1 individual with a straight hairline (ww).

These examples demonstrate how monohybrid crosses can be used to predict the genotypic and phenotypic ratios of offspring based on the inheritance patterns of a single trait controlled by a single gene.

What Is a Test Cross?

In the realm of genetics, when the genotype of an individual expressing a dominant trait is unknown, a test cross serves as a valuable tool to determine whether the individual is heterozygous or homozygous. This cross involves breeding the individual of interest with another individual that is known to be homozygous recessive for the specific trait under investigation. By examining the phenotypes of the resulting offspring, one can deduce the genotype of the unknown individual. The expected ratios of phenotypes in the offspring can be predicted using a Punnett square.

Test Cross 1

Test Cross 1	G	(g)
g	Gg	gg
g	Gg	gg

Let’s consider an example to illustrate the concept of a test cross. Previously, we discussed pod color, where the dominant trait is green (G) and the recessive trait is yellow (g). In Test Cross 1, a plant with unknown genotype (Gg) is crossed with a plant that has a homozygous recessive genotype (gg) for yellow pod color. The offspring exhibit both green (Gg) and yellow (gg) phenotypes. The observed ratio of phenotypes is 1:1, with half of the offspring being yellow and the other half being green.

Test Cross 2

Test Cross 2	G	(G)
g	Gg	Gg
g	Gg	Gg

In Test Cross 2, a plant with the same unknown genotype (Gg) is crossed with a plant that is homozygous dominant (GG) for green pod color. In this scenario, all the offspring display the green phenotype (Gg). This outcome confirms that the unknown individual carries a heterozygous genotype (Gg) for pod color.

By analyzing the phenotypic ratios in the offspring resulting from the test crosses, we can determine the genotype of the individual expressing the dominant trait. In the case of a 1:1 ratio, it indicates a heterozygous genotype, whereas a uniform dominant phenotype in the offspring suggests a homozygous dominant genotype.

The test cross serves as a powerful tool in genetics to uncover the genetic makeup of individuals expressing dominant traits. It allows researchers to discern whether the unknown individual carries two identical copies of the dominant allele (homozygous) or one dominant and one recessive allele (heterozygous). This information is crucial for understanding inheritance patterns and unraveling the complexities of genetic traits.

In summary, a test cross involves crossing an individual of unknown genotype expressing a dominant trait with another individual that is homozygous recessive for that trait. By examining the phenotypes of the offspring, researchers can deduce whether the unknown individual is heterozygous or homozygous for the trait in question. The test cross provides valuable insights into the genetic composition of individuals and contributes to our understanding of inheritance patterns.

Advantages of Monohybrid Cross

• Simplicity: Monohybrid crosses involve the study of a single trait, making them relatively straightforward to understand and analyze compared to more complex crosses involving multiple traits.
• Clear Mendelian Inheritance Patterns: Monohybrid crosses allow for the clear observation of Mendelian inheritance patterns, such as the segregation of alleles and the dominance of certain traits over others. This simplicity helps in establishing basic principles of inheritance.
• Predictability: Monohybrid crosses enable the prediction of genotypic and phenotypic ratios in offspring, providing a level of predictability in understanding trait inheritance. This is particularly useful in selective breeding programs and genetic counseling.
• Basic Building Block: Monohybrid crosses serve as a foundation for understanding more complex genetic concepts, such as dihybrid crosses and other patterns of inheritance. They provide a starting point for comprehending genetic principles and establishing a solid understanding of genetics.

Limitations of Monohybrid Cross

• Limited Scope: Monohybrid crosses focus on the inheritance of a single trait, which may not capture the complexity of genetic interactions and inheritance patterns that occur in real-world scenarios. Many traits are influenced by multiple genes and can exhibit more intricate inheritance patterns.
• Lack of Consideration for Linked Genes: Monohybrid crosses do not account for the phenomenon of genetic linkage, where genes located close to each other on the same chromosome tend to be inherited together. This limitation overlooks the possibility of linked genes affecting trait inheritance.
• Oversimplification of Genetics: Monohybrid crosses provide a simplified view of genetics and may not fully represent the complexities of genetic inheritance and gene interactions. Real-world genetics involves the interplay of multiple genes, environmental factors, and epigenetic influences that are not accounted for in monohybrid crosses.
• Incomplete Understanding of Phenotypic Variations: Monohybrid crosses do not address the full range of phenotypic variations observed in nature. Many traits are influenced by a combination of genetic and environmental factors, and monohybrid crosses alone may not provide a comprehensive understanding of these variations.
• Limited Application to Complex Traits: Monohybrid crosses may not be suitable for studying complex traits that are controlled by multiple genes and exhibit polygenic inheritance. Complex traits, such as height or intelligence, require the consideration of multiple genes and their interactions, which monohybrid crosses cannot adequately address.

Uses of Monohybrid Cross

• Understanding Mendelian Inheritance: Understanding Mendelian Inheritance Gregor Mendel used monohybrid crosses to establish the principles of inheritance in his experiments with pea plants. Mendel formulated his laws of segregation and dominance by observing the patterns of trait transmission across generations.
• Determining Dominant and Recessive Traits: Monohybrid crosses are used to determine whether a trait is dominant or recessive. By crossing individuals with known traits and observing the phenotypes of their progeny, scientists can determine whether a trait is dominant or recessive.
• Predicting Genotypic and Phenotypic Ratios: Monohybrid crosses enable for the prediction of the genotypic and phenotypic ratios of the offspring. Scientists can estimate the likelihood of particular genotypes and phenotypes arising in the offspring of a cross using Punnett squares or mathematical calculations.
• Selective Breeding: In selective breeding programs, monohybrid crosses are utilized to produce progeny with desired traits. Breeders can increase the frequency of desirable traits in subsequent generations by selectively mating individuals with particular phenotypes.
• Genetic Counseling: Monohybrid crosses can be utilized in genetic counseling to determine the likelihood of inheriting particular genetic disorders or traits. By analyzing the genotypes of parents and employing monohybrid crosses, genetic counselors can determine the likelihood of passing on particular traits to progeny.
• Plant and Animal Breeding: In plant and animal breeding programs, monohybrid crosses are utilized to enhance the quality and characteristics of crops and livestock. Breeders can create offspring with enhanced traits, such as increased yield, disease resistance, or specific physical characteristics, by meticulously selecting parent individuals with desired traits and conducting monohybrid crosses.
• Evolutionary Studies: Monohybrid crosses can provide insights into the genetic diversity and evolutionary processes of populations for evolutionary studies. By analyzing the distribution of traits within a population and examining inheritance patterns, scientists can obtain a better understanding of how traits are transmitted and how they may evolve over time.

Monohybrid Cross vs Dihybrid Cross – What is the differences between Cross and Dihybrid Cross?

Differences	Monohybrid Cross	Dihybrid Cross
Number of Traits	Involves the study of a single trait	Involves the study of two different traits simultaneously
Parental Generation	Involves two purebred parents for one trait	Involves two purebred parents for two different traits
Gametes	Only one type of gamete is produced	Two different types of gametes are produced
Punnett Square	Requires a 2×2 Punnett square	Requires a 4×4 Punnett square
Genotype Possibilities	Produces three possible genotypes	Produces nine possible genotypes
Phenotype Possibilities	Produces two possible phenotypes	Produces four possible phenotypes
Alleles	Deals with one pair of alleles	Deals with two pairs of alleles
Law of Segregation	Demonstrates the segregation of alleles during gamete formation	Demonstrates the segregation of alleles for two different traits during gamete formation
Law of Independent Assortment	Not applicable	Demonstrates the independent assortment of alleles for two different traits during gamete formation
Inheritance Patterns	Shows patterns of dominance, recessiveness, or co-dominance for a single trait	Shows patterns of dominance, recessiveness, or co-dominance for two different traits
Example	Crossing two purebred tall and short pea plants	Crossing two purebred yellow and green pea plants for seed color and roundness
Genetic Ratio	Produces a 1:2:1 genotypic ratio	Produces a 1:2:2:4:1:2:1:2:1 genotypic ratio
Phenotypic Ratio	Produces a 3:1 phenotypic ratio	Produces a 9:3:3:1 phenotypic ratio
Application	Used to study inheritance patterns of a single trait	Used to study inheritance patterns of multiple traits simultaneously
Mendel’s Experiments	Mendel’s experiments on pea plants were primarily monohybrid crosses	Mendel’s experiments on pea plants involved both monohybrid and dihybrid crosses

Monohybrid cross Practice

In pea plants, the gene for flower color has two alleles, P (purple) and p (white). If a plant with the genotype Pp is crossed with a plant with the genotype pp, what will be the phenotypic ratio of the offspring?
a) 1:1 purple to white
b) 3:1 purple to white
c) 1:2:1 purple to white
d) 1:3 purple to white

In cats, the gene for fur color has two alleles, B (black) and b (brown). If a heterozygous black cat (Bb) is crossed with a brown cat (bb), what is the probability of the offspring being black?
a) 0%
b) 25%
c) 50%
d) 75%

In corn plants, the gene for kernel texture has two alleles, S (starchy) and s (sweet). If a homozygous starchy corn plant (SS) is crossed with a homozygous sweet corn plant (ss), what will be the genotypic ratio of the offspring?
a) 1:0 starchy to sweet
b) 1:1 starchy to sweet
c) 3:1 starchy to sweet
d) 1:2:1 starchy to sweet

In mice, the gene for coat color has two alleles, C (black) and c (white). If a heterozygous black mouse (Cc) is crossed with a white mouse (cc), what will be the phenotypic ratio of the offspring?
a) 1:0 black to white
b) 1:1 black to white
c) 3:1 black to white
d) 1:2:1 black to white

In chickens, the gene for comb shape has two alleles, R (rose comb) and r (single comb). If two heterozygous chickens (Rr) are crossed, what is the probability of the offspring having a rose comb?
a) 0%
b) 25%
c) 50%
d) 75%

In fruit flies, the gene for eye color has two alleles, B (red eyes) and b (white eyes). If a heterozygous fruit fly (Bb) is crossed with a white-eyed fruit fly (bb), what will be the genotypic ratio of the offspring?
a) 1:0 red eyes to white eyes
b) 1:1 red eyes to white eyes
c) 3:1 red eyes to white eyes
d) 1:2:1 red eyes to white eyes

In rabbits, the gene for fur texture has two alleles, F (long fur) and f (short fur). If a homozygous long-furred rabbit (FF) is crossed with a homozygous short-furred rabbit (ff), what will be the phenotypic ratio of the offspring?
a) 1:0 long fur to short fur
b) 1:1 long fur to short fur
c) 3:1 long fur to short fur
d) 1:2:1 long fur to short fur

In roses, the gene for flower scent has two alleles, S (fragrant) and s (non-fragrant). If a homozygous fragrant rose (SS) is crossed with a non-fragrant rose (ss), what is the probability of the offspring being fragrant?
a) 0%
b) 25%
c) 50%
d) 100%

In horses, the gene for coat color has two alleles, C (chestnut) and c (black). If a homozygous chestnut horse (CC) is crossed with a black horse (cc), what will be the genotypic ratio of the offspring?
a) 1:0 chestnut to black
b) 1:1 chestnut to black
c) 3:1 chestnut to black
d) 1:2:1 chestnut to black

In dogs, the gene for tail length has two alleles, T (long tail) and t (short tail). If a heterozygous long-tailed dog (Tt) is crossed with a short-tailed dog (tt), what will be the phenotypic ratio of the offspring?
a) 1:0 long tail to short tail
b) 1:1 long tail to short tail
c) 3:1 long tail to short tail
d) 1:2:1 long tail to short tail

In sunflowers, the gene for petal color has two alleles, Y (yellow) and y (red). If a homozygous yellow sunflower (YY) is crossed with a heterozygous yellow sunflower (Yy), what will be the phenotypic ratio of the offspring?
a) 1:0 yellow to red
b) 1:1 yellow to red
c) 3:1 yellow to red
d) 1:2:1 yellow to red

In tomatoes, the gene for fruit shape has two alleles, R (round) and r (oval). If a heterozygous round tomato plant (Rr) is crossed with an oval tomato plant (rr), what is the probability of the offspring having round fruits?
a) 0%
b) 25%
c) 50%
d) 75%

In butterflies, the gene for wing pattern has two alleles, W (striped) and w (spotted). If a homozygous striped butterfly (WW) is crossed with a heterozygous striped butterfly (Ww), what will be the genotypic ratio of the offspring?
a) 1:0 striped to spotted
b) 1:1 striped to spotted
c) 3:1 striped to spotted
d) 1:2:1 striped to spotted

In peas, the gene for seed shape has two alleles, S (smooth) and s (wrinkled). If a smooth-seeded pea plant (SS) is crossed with a wrinkled-seeded pea plant (ss), what will be the phenotypic ratio of the offspring?
a) 1:0 smooth to wrinkled
b) 1:1 smooth to wrinkled
c) 3:1 smooth to wrinkled
d) 1:2:1 smooth to wrinkled

In mice, the gene for coat length has two alleles, L (long) and l (short). If a heterozygous long-haired mouse (Ll) is crossed with a short-haired mouse (ll), what is the probability of the offspring having long hair?
a) 0%
b) 25%
c) 50%
d) 75%

Answers:

b) 3:1 purple to white
c) 50%
c) 3:1 starchy to sweet
c) 3:1 black to white
c) 50%

b) 1:1 red eyes to white eyes
b) 1:1 long fur to short fur
c) 50%
b) 1:1 chestnut to black
c) 3:1 long tail to short tail
c) 3:1 yellow to red
b) 25%
c) 3:1 striped to spotted
c) 3:1 smooth to wrinkled
b) 25%

FAQ

References

• Monohybrid Crosses and Segregation. (2021, August 12). University of Arkansas at Little Rock. https://bio.libretexts.org/@go/page/25731
• https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/monohybrid-cross
• https://biologydictionary.net/monohybrid-cross/
• https://www.aakash.ac.in/important-concepts/biology/monohybrid-cross-inheritance-one-gene
• https://www.thoughtco.com/monohybrid-cross-a-genetics-definition-373473
• http://www.biology.arizona.edu/mendelian_genetics/problem_sets/monohybrid_cross/01q.html
• https://thebiologynotes.com/monohybrid-cross/
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