The titled question is one of the basics and most asked questions during the class. The same happened to me when a student asked to differentiate between monohybrid and dihybrid cross. I always answer such a question in two steps i.e., first I give a quick brief, then I explain every concept in a deeper sense.
Here is my short answer to differentiate between Dihybrid and Monohybrid cross.
The latter focuses on a single trait, whereas the former explores the inheritance of two distinct traits in the same genetic cross.
Now let’s dig deeper into it. Here’s my detailed answer.
There are two breeding methods in organisms specifically known as the Monohybrid and Dihybrid cross methods. Both methods are individually defined with proper examples below.
Monohybrid Cross
A monohybrid cross involves the examination of the inheritance patterns of a single trait. This means that in this type of genetic cross, we intend to study two individuals that differ by one character trait of our interest.
Example: Let us illustrate through an example. We are interested in color of a plant’s flower. Since this character is controlled by a gene in the parent plant. Each gene has two versions (known as alleles) for this trait (flower color in our case). Now the nature of these alleles will decide the offspring’s color of the flower.
Each counterpart of this cross has three possibilities that are:
1. Homozygous Dominant: Both alleles are identical and dominant. Usually denoted by “AA” where both alphabets are capital, meaning dominance.
2. Homozygous Recessive: Both alleles are identical but recessive. Usually denoted by “aa” where both alphabets are in small letters, showing recessive property.
3. Heterozygous: Alleles are not the same. One is dominant while the other is recessive. Denote by “Aa” or “aA”, both have same meanings. Which means one of the alleles is dominant and the other is recessive.
To perform a monohybrid cross and estimate an expected trait appearance in the offspring. A Punnett square can be drawn either online or by-hand. A pictorial example can be seen below.
Dihybrid Cross:
A dihybrid cross is a genetic experiment that investigates the inheritance patterns of two different traits simultaneously in organisms. It explores how alleles (alternative forms of a gene) for two separate characteristics are inherited and expressed in offspring.
Example of a Dihybrid Cross
Let’s take an example of pea plants to illustrate a dihybrid cross. Consider two traits: seed color and seed texture. In pea plants, seed color can be yellow (dominant allele, denoted as A) or green (recessive allele, denoted as a). Similarly, seed texture can be smooth (dominant allele, denoted as B) or wrinkled (recessive allele, denoted as B).
Imagine crossing two pea plants that are heterozygous for both traits (AaBb x AaBb). Using a Punnett square, we can predict the possible genetic combinations of their offspring. The resulting grid would demonstrate various genotypes and phenotypes, showing the probability of different seed color and texture combinations in the next generation. For your information, our have a dihybrid cross calculator on the main page which can generate the Punnett square and genotype-phenotype ratio in seconds.