The Difference between Test Cross and Backcross in Genetics
When it comes to genetic breeding, there are two common terms used to describe the process of mating between two different individuals – test cross and backcross. Although both terms describe a type of breeding, there are major differences between the two.
Test Cross
A test cross is a type of breeding where one of the parents is unknown. Typically, a purebred organism is crossed with an unknown individual to determine its genetic makeup. The purebred organism is usually homozygous, meaning that it has two identical copies of the same gene. On the other hand, the unknown organism is usually heterozygous, meaning that it has two different versions of the same gene.
The purpose of a test cross is to determine the genotype (the genetic makeup) of the unknown organism by examining the phenotype (observable traits) of the offspring produced from the cross. If the unknown organism is homozygous, all the offspring will have the same phenotype. If the unknown organism is heterozygous, the offspring’s phenotype will display a 3:1 ratio of dominant to recessive alleles.
Backcross
A backcross is another type of breeding where one of the parents is a hybrid or a heterozygous organism. In a backcross, the hybrid is crossed with one of its parents or a purebred organism. The aim of a backcross is to enhance desirable traits that the hybrid organism possesses.
The offspring produced through a backcross will have a 50% chance of inheriting the desired trait from the hybrid parent. If the offspring inherits the trait, it is called a backcrossed organism.
Key Differences
The major difference between a test cross and a backcross is the purpose of the breeding. A test cross is used to determine the genetic makeup of an unknown organism, while a backcross is used to enhance desirable traits in a hybrid organism.
Another difference between the two is the type of parent used in the breeding process. In a test cross, a purebred organism is used, while in a backcross, a hybrid or heterozygous organism is used.
Finally, the expected results of a test cross and a backcross are different. In a test cross, the expected outcomes are predictable based on the phenotype of the offspring. However, in a backcross, the desired trait may or may not be passed on to the offspring.
In conclusion, understanding the differences between test cross and backcross is crucial for geneticists and breeders. It will enable them to choose and implement the appropriate breeding strategy to obtain the desired offspring.
Table difference between test cross and backcross
| Test Cross | Backcross |
|---|---|
| It involves crossing an organism with a homozygous recessive individual. | It involves crossing an organism with one of its parental types. |
| The purpose is to determine whether the organism is homozygous or heterozygous for a particular gene. | The purpose is to reintroduce a desirable trait from one of the parents back into the offspring. |
| It helps in determining the genotype of a dominant trait in an organism. | It helps in restoring the original genetic makeup of an organism. |
| It is usually done for experimental purposes. | It is usually done in agriculture for plant and animal breeding purposes. |