Any organism is nothing but a by-product of its genetic makeup and environment. If you want to learn about it in detail, then you have to know the genetic vocabulary, terms, and concepts. This article talks about the test cross and how it helps recognize the genotype. It gets performed between an organism exhibiting the dominant trait and another organism displaying the recessive trait. Gregor Mendel, also famous as the father of modern genetics, is the founder of test cross. Before you understand the difference between back cross and test cross, you must know what a test cross is? This article takes you through it all, so sit back and keep reading till the end.

What are Genotype and Phenotype?

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In biology, a gene refers to a section of DNA that encodes a trait. The particular arrangement of nucleotides (each composed of a phosphate group, sugar, and a base) in a gene can vary from copies of the same gene. Thus, a gene can occur in various forms across organisms. Those various forms are nothing but alleles. The precisely fixed position on the chromosome that contains a specific gene is a locus.

A diploid organism has two copies of a single allele or one copy of two different alleles from their parents. When the individual inherits two similar alleles, it means they have a homozygous genotype at that locus. But, if they have two different alleles, then it refers to a heterozygous genotype at that locus. A subsequent combination of alleles possessed by an individual for a specific gene is their genotype.

Phenotype refers to a total of an organism's observable characteristics. The primary difference between genotype and phenotype is that genotype gets inherited from the parents of an organism. And phenotype is the opposite. The phenotype, however, does get influenced by genotype and not vice versa. Factors like epigenetic modifications, environment and lifestyle do affect the phenotype.

What is a Test Cross?

A test cross is a method of exploring the genotype of an organism. Earlier, the test cross got used as an experimental mating test to figure out the alleles present in the genotype. During the test cross, the F1 hybrid gets crossed back with the recessive parent.

In simple words, the test cross is the cross of an organism having an unknown dominant genotype with an organism that is homozygous recessive for that trait. Test cross can help you determine if the individual getting tested is homozygous dominant or heterozygous dominant.

What is a Back Cross?

Backcross refers to the mating of hybrid organisms with one of its parents or an organism that is genetically equivalent to the parent. In other words, breeding of F1 hybrids with either of the two parents gets referred to as a backcross.

The backcross is helpful in genetics studies to isolate particular characteristics in a related group of animals or plants. In animal breeding, backcross also gets called a top cross. It gets widely used in horticulture, animal breeding, and for the production of gene knockout organisms.

Back cross example – particular crop plant hybrids get backcrossed with wild species to recover their helpful traits like high yield, disease resistance, etc.

The fundamental difference between the test cross and backcross is that the test cross gets used to discriminate against the genotype of a phenotypically dominant individual. And backcross gets used to recover an elite genotype from a parent carrying it.

Difference Between Back Cross and Test Cross

Test Cross	Back Cross
It is a cross between the dominant phenotype and the recessive phenotype.	It is the cross between F1 hybrid with any of the parents.
Test cross helps with figuring out the genotype of the dominant phenotype.	Backcross helps with recovering helpful characteristics in the parental population.
All test crosses are backcrosses too.	Backcross of an F1 hybrid with a recessive phenotype can get called as a test cross.
The F1 hybrid gets crossed with a recessive genotype during test cross.	F1 hybrid gets crossed with either heterozygous genotype or homozygous dominant during backcross.
Test cross helps identify the zygosity of the dominant phenotype.	Backcross helps with recovering elite genotypes.

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FAQs on How Does a Test Cross Help in Identifying the Genotype?

Question 1: Define the Test Cross and State its Importance.

Answer: The crossing of an F11 progeny with a double (homozygous) recessive parental progeny gets done to figure out if the progeny is homozygous or heterozygous for a character under consideration. It is nothing but a test cross.

Importance of the test cross: the test cross gets conducted to figure out the genotype of a dominant parent and check whether it's a homozygous or heterozygous dominant. Further, you get results in the ratio of the offspring, based on which you can predict the genotype carried by the parent. If all the offspring belong to a single phenotype, then it's a homozygous-dominating parent. If you notice a 1:1 ratio in the organism's phenotype, then it's a heterozygous-dominating parent.

Question 2: Explain in Brief: How Does a Test Cross Help Identify the Genotype of an Organism?

Answer: You must know that the test cross gets conducted to determine if an organism having a dominant phenotype is heterozygous or homozygous for the trait. Also, note that cross gets carried out between a homozygous recessive organism and another organism with a dominant phenotype.

If the organism displaying dominant phenotype has homozygous alleles, then the resulting F1 generation will have all organisms with dominant characters. And their genotype will be heterozygous for the trait.
On the other hand, organisms having a heterozygous genotype for the dominant trait results in F1 generation, where half of the organisms have the dominant phenotype. And rest half of the organisms have the recessive phenotype.

Such a cross can get represented by a cross for the yellow (dominant) or green (recessive), below is a pod feature of a pea plant.