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Punnett Square, test cross, mono/di-hybrids

Explain the test - cross. I have to explain the usefullness of the test-cross. I had my paper written then was told I need to incorporate the Punnett square, monohybrid cross, dihybrid cross etc. into the paper. I am now confused - maybe I have just researched so much I cannot make sense of any of it. How is the Punnett Square, test cross, monohybrid cross, dihybrid cross all tied in together?

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Let's start with simple definitions for these terms (from http://www.thefreedictionary.com):

Punnett Square-Â A method for predicting the ratios of phenotypes in offspring, given the phenotypes and/or genotypes of the parents. Generally, the alleles of two or fewer genetic loci are worked with per square.

Test cross- a cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait so the unknown genotype can be determined from that of the offspring.

monohybrid cross- hybridization (breeding) using ...

Solution Summary

Definitions and relation between test crosses, monohybrids, dihybrids and Punnett squares.