I have a phenotypically purple flowered pea plant with the flowers located along the stem. How do I determine the genotypes and do test crosses on the homozygous and heterozygous genotype and determine the genotype and phenotype ratios of each cross? The process is explained.© BrainMass Inc. brainmass.com November 29, 2021, 11:55 pm ad1c9bdddf
I have also included this as an attachment as the Punnett Square did not paste well below.
Gregor Mendel was an Austrian monk who was one of the first to quantify inheritance. He, like your question, also chose a pea plant for his work. Others had used pea plants successfully at the time Mendel was doing his work and knew that specific properties (color, wrinkled seeds, size) would hybridize. In hybridization, different strains of a species can be crossed to produce fertile offspring.
In addition, peas have a short generation time (the time from parents producing offspring to the offspring becoming parents themselves), are easy to grow and have easily distinguishable traits. But peas have a unique inflorescence (flower). Both the male and female organs are contained in the flower, so if pollen from another plant does not come by, all is not lost. It can self-pollinate, use the male and female parts in the same flower, to produce offspring. In this way, the experiment could be controlled. The male parts of a flower could be removed and then other pollen can be introduced manually (such as on the tip of a paintbrush). This is called cross-pollination (Raven and Johnson 1999).
The phenotype is the observable structural and functional characteristics of an organism; the genotype is the hereditary or genetic makeup of an organism (Lincoln and Boxhall 1990).
In other words, the genotype is "the genes" and the phenotype is "what you see".
Once organisms, in this case pea plants, are crossed, they provide offspring. The Latin word for "son" is "filius" (also the origin if the word, "affiliation"). The early scientists decided to name the first generation the first filial or F1 generation ("the sons", even though there may be daughters running around there too!) The second generation would be the F2 ...
Test crosses are demonstrated. The test crosses on the homozygous and heterozygous genotypes are analyzed.