The key difference between reciprocal cross and test cross is that the reciprocal cross determines the sex-linked inheritance; that is whether the trait depends on the parent sex or not, while the test cross determines the zygosity of the trait; that is whether it is heterozygous or homozygous.
There are different types of genetic crosses in breeding programs to determine the genetic basis of traits and their inheritance. Reciprocal cross, test cross and back cross are popular tests among them. The reciprocal test mainly reveals whether the trait is autosomal or sex-linked. Test cross reveals whether the trait is homozygous or heterozygous while backcross helps to produce an offspring that is genetically very close to the recurrent parent. But, this article mainly focuses on discussing the difference between reciprocal cross and test cross.
CONTENTS
1. Overview and Key Difference
2. What is Reciprocal Cross
3. What is Test Cross
4. Similarities Between Reciprocal Cross and Test Cross
5. Side by Side Comparison – Reciprocal Cross vs Test Cross in Tabular Form
6. Summary
What is a Reciprocal Cross?
The reciprocal cross is a test that determines the role of the parent sex in the inheritance of a trait. In simple words, it reveals whether a trait is sex-linked or not (autosomal).
Figure 01: Sex-linked Inheritance in Drosophila
To assess that, it is necessary to carry out a reciprocal cross between a male of the homozygous for that trait with an individual who does not have the same trait. Similarly, it can be done between a female of the homozygous for that trait with an individual who does not have the same trait.
What is a Test Cross?
The test cross is a genetic cross that determines the zygosity of the parent for the trait. In simple words, test cross reveals whether the unknown dominant phenotype parent is heterozygous or homozygous for that trait. To find this out, it is necessary to carry out the test cross between an individual with an unknown dominant phenotype with an individual (parent) homozygous recessive for that trait.
Figure 02: Test Cross
If a test cross produces all identical offsprings, it indicates that the parent is homozygous for that trait. On the other hand, if the test cross produces 1:1 ratio of two types of offsprings, it indicates that the parent is heterozygous for that trait.
What are the Similarities Between Reciprocal Cross and Test Cross?
- Reciprocal cross and test cross are two genetic crosses.
- Both reveal the genetic basis of traits.
- Moreover, they both involve a cross between two individuals.
What is the Difference Between Reciprocal Cross and Test Cross?
The reciprocal cross reveals the linkage of a trait with sex chromosomes while the test cross reveals the homozygous or heterozygous nature of a trait. So, this is the key difference between reciprocal cross and test cross. Moreover, in a reciprocal cross, the cross happens between a male (or a female) homozygous for a trait with an individual who does not have that trait. In a test cross, the cross occurs between an unknown dominant phenotype with an individual (parent) homozygous recessive for that trait. Therefore, we can consider this too as a significant difference between reciprocal cross and test cross.
The below infographic shows more comparisons regarding the difference between reciprocal cross and test cross.
Summary – Reciprocal Cross vs Test Cross
In summary, the reciprocal cross and test cross are two frequently used genetic crosses. Reciprocal cross tells whether the trait is linked to sex chromosomes or not. But, test cross tells whether the parent is homozygous or heterozygous for the trait. So, this is the key difference between reciprocal cross and test cross.
Reference:
1. “Reciprocal Cross.” Wikipedia, Wikimedia Foundation, 14 June 2019, Available here.
2. “Test Cross (Genetics) – Definition and Examples.” Biology Dictionary, 26 Aug. 2018, Available here.
Image Courtesy:
1. “Sex-linked inheritance” By GYassineMrabetTalk✉This W3C-unspecified vector image was created with Inkscape. – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Figure 12 02 03” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia
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