Test Crossing: How is the genotype of an organism identified?

Test Crossing is a process of studying the genotype of an organism. It determines whether a dominant phenotype is homozygous or heterozygous for a specific allele. Usually, one allele has the power to dominate another allele. Therefore, it can mask it, which will make it tough to determine what kind of allele an organism possesses.

All organisms with unknown genotype are crossed with a homozygous organism to achieve a recessive trait. After that, the offspring of the test cross will be observed to see how this test crossing is going. In case, there is any recessive offspring; the unknown parent organism will possess heterozygous alleles. However, if there is dominant offspring, the parent organism will have homozygous dominant alleles.

Gene Mapping: Crossover Frequencies

Gene mapping is a method of determining the location of genes within the chromosomes. This approach can recognize the distance between genes as well as the frequency of the recombination process. If the genes are closer, it is less probable that they will be isolated in the crossover stage. Besides, they will pass on to the next generation together.

Gene mapping also gives us valuable information about the chance of the inheritance of any existing disorders. This information is critical for an effective biometric system such as – accuracy, throughput rate, speed, the uniqueness of the biometric organ and action, acceptability to users, reliability, resistance to counterfeiting, etc.

The Statistical methods used for Test Crossing

There are two basic rules of probability for solving problems in genetics – Multiplication and Addition. The multiplication rule includes – independent events in a sequence and questions with ‘And.’ The addition rule contains mutually exclusive events with questions with ‘Or.’

Other methods include – the nature of inheritance where we will draw a test cross and apply the chi-squared test. The chi-squared test is a process of determining the actual and expected results. The following is the formula for a chi-squared test.

x2 = Σ[(obs. – exp.)2 / exp.]

obs. = observed data

exp. = expected data

To conclude, the above process clearly explains how test crossing is conducted to the genotype of an organism.