Dihybrid Cross Definition, Steps, Process, and Examples

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Definition of Dihybrid Cross

A dihybrid crossing is a gene-cross between people who have homozygous or heterozygous genotypes that have two distinct characteristics or traits. Dihybrid crosses differ from the monohybrid crossing that only involves one genetic character or characteristic. The dihybrid cross is more complicated than monohybrid ones since they contain several genetic characteristic in which the parents could be homozygous or heterozygous in these traits.

The dihybrid is employed as a way to test or establish that the principle of independence is true. selection as it establishes that two characters separate independently from each other. But, it is only applicable when there are genes that aren’t connected and reside across different chromosomes. There are more gametes that are formed in a dihybrid crossing is greater than the number of gametes formed during an unihybrid cross because two distinct genes are at play in an adihybrid crossing.

There are more offspring. This can be greater in dihybrid crosses. They exhibit a greater different phenotypic characteristics than those that result from monohybrid crosses. The phenotypic proportion of offsprings of the first generation following a dihybrid cross is listed as 9:3 3:1. The offspring’s genotypes are also more diverse, by the ratio 1:2:2 4:1 2:1 2:1.

Steps/Process of Dihybrid Cross

These are the steps to follow to perform a dihybrid cross between two individuals.

1. Selection of parents

The initial step of the dihybrid crossing is the selection of the characters and parents who will be crossed. Pure lines are established by selfing the people for three generations . This confirms the existence in pure lines.

2. Designation for the characters

The alleles that belong to the two characters chosen are identified with specific alphabetic characters. Alleles that are dominant will be designated by uppercase letters, and recessive ones are identified with lowercase letters.

3. Punnet square

Because gametes are created for fertilization, gametes are created. Four distinct gametes can be formed as you study both characters. Punnet is a gamete that was created when studying the two characters. Punnet square is constructed using the information about the phenotype as well as genotype of both parents. The gametes are haploid as consequence of the meiotic division. The combinations that are possible between the genotypes are incorporated in the Punnet square. All combinations are equally feasible since fertilization processes are random.

4. Determination of ratios

After all combinations have been identified, the phenotypic and genotypic proportions of offsprings are recorded down.

Examples of Dihybrid Cross

1. Dihybrid cross in Pea plants

A dihybrid is the cross between a pea plant homozygous that has round, yellow seeds as well as dried green seeds. Round yellow seeds have been represented by the RRYY alleles, while the green seeds that are wrinkled are represented by  rryy. The gametes resulting from the two alleles are RY and the ry. When two parents cross, F1 hybrids bearing the RrYy allele are created. The hybrids are oval yellow seedlings (RrYy) that carry the predominant roundness allele and that dominant allele Y that is responsible for the yellow hue.

The four alleles are able to combine into four combinations: RY, Ry, rY, and ry. The four alleles are mixed randomly, resulting in four different types of gametes. Gametes are generated randomly in fertilization, resulting in sixteen different kinds of individuals in the generation known as F2. The hybrids appear in the combination of 9 rounds of yellow 3 round greens and 3 wrinkled yellow and one wrinkled green.

Dihybrid cross in Pea plants
Dihybrid cross in Pea plants

2. Dihybrid cross in Drosophila

Another instance of a cross that is a dihybrid can be seen in cases of homozygous long winged black-bodied Drosophila and grey-bodied, vestigial-winged fly. It is believed that the F1 generation hybrids are grey-bodied long-winged Drosophila fly. After mating, the hybrids with one another, create The F2 generation. The F2 generation comprises 9 grey bodies with long wings, three long-winged black bodies, three vestigial-winged grey bodies, and 1 old-fashioned winged black-bodied Drosophila.

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