Main Difference
Altering traits of species while crossing over according to Mendel’s model is divided in to two broad categories, Monohybrid cross and Dihybrid cross. The main difference between monohybrid an dihybrid is, monohybrid involves one gene as a set of allele, for example color of a plant while dihybrid involves two set of genes for example color and height.
Monohybrid
A cross involving divergent expression of one trait is transferred to as monohybrid cross. In monohybrid allele one gene is required to cross over. For example, crossing of phenotypically yellow homozygous dominant plant color (YY) with phenotypically green homozygous recessive plant colour (yy), the gametes will be heterozygous dominant. The genotype will look like Yy and phenotypically it will be yellow. So if then we cross two F1 plants gene, the possible genotypes of F2 generation will be, one homozygous dominant specie (YY) which will be phenotypically yellow, two heterozygous dominant (Yy) which will also be yellow and one homozygous recessive (yy) which will be green phenotypically. The phenotypic ratio becomes 3:1. It tells the outcome of just one trait. This one character is responsible to bring about the change in specie.
Dihybrid
Dihybrid cross involves a pair of gene. It means two characteristics are used to cross over. For example, pea color and shape. First step is to find all possible allele combinations. From the monohybrid cross we know that genotypically, one or two Y alleles will turn the pea yellow phenotypically while genotypically (yy) will lead to green colour of pea phenotypically. But there are also two alleles that determine the shape of the pea. They can be round or wrinkled. The genotypically dominant allele R can turn the pea in round shape. The recessive gene r will cause the pea to be wrinkled phenotypically. So if you cross a homozygous dominant round yellow plant, genotypically (RRYY), with a homozygous recessive, wrinkled green plant, genotypically (rryy) the gametes will be RY and ry. All the plants phenotypically will be round and yellow but they will all be heterozygous for both the characteristics genotypically (RrYy). So if then we cross two F1 plants the possible gametes will be RY, Ry, rY and ry genotypically. F2 generation will me more mixed, there will be 9:3:3:1 ratio of round yellow to wrinkled yellow to round green to wrinkled green respectively. Dihybrid crosses are used to predict two traits at the same time.
Key Differences
- Cross between two perfect specie to study the inheritance of one gene involved is called monohybrid cross over while a cross between two pure organisms involving two pair of genes is called Dihybrid crossing.
- In monohybrid cross only one characteristic is focused phenotypically as well as genotypically while in Dihybrid cross two characters are crossed together to generate the result.
- Mendel focused on monohybrid crossing over first then he further assessed it by introducing Dihybrid model.
- Phenotypically in monohybrids cross over ratio of 3:1 is produced in second generation while in Dihybrid cross over ratio of 9:3:3:1 is produced in second generation.
- Monohybrid cross produces genotypic ratio of 1:2:1 in second generation while the Dihybrid cross over produce genotypic ratio of 1:2:1:2:4:2:1:2:1.
- The test cross ratio of monohybrids is -1:1 while Dihybrid is -1:1:1:1.