Question

You notice that in most biology and genetics textbooks, the authors show that Gregor Mendel used flower color as one of his pairs of traits. The purple flower phenotype is dominant to the white flower phenotype. However, if you go back to Mendel's experiments, you see that he actually studied seed coat color. The purple seed coat phenotype was dominant to the white seed coat phenotype. Mendel did note that plants with purple seed coats had purple flowers and plants with white seed coats had white flowers.

Is the gene for seed coat color pleiotropic because it also affects flower color, or are the seed coat color gene and the flower color gene very closely linked? To find out the answer to this question, you assume that the genes for flower color and seed coat color are different genes, and your null hypothesis is that they assort independently. You designate the flower color gene wf and the seed coat color gene sw. Plants that are WF__, SW___ have purple flowers and purple seed coats. Plants that are wf wf, ws ws have white flowers and white seed coats.
You do the testcross WF wf, SW sw X wf wf, sw sw and collect 15,206 offspring. What result would tell you that the wf and sw loci are probably the same, pleiotropic locus?

Answer 1

To determine if the genes for seed coat color and flower color are pleiotropic or closely linked, you can perform a testcross between them. Analyzing the phenotypes of the offspring can help determine if the genes are pleiotropic or not.

Step-by-step explanation:

To determine if the gene for seed coat color and the gene for flower color are pleiotropic or closely linked, you can perform a testcross between the two genes. In this case, you would cross a plant with purple flowers and purple seed coats (WF wf, SW sw) with a plant with white flowers and white seed coats (wf wf, ws ws).

If the genes are pleiotropic, you would expect all the offspring to have either purple flowers and purple seed coats or white flowers and white seed coats. However, if the genes are closely linked, you would expect to see some variation in the offspring, such as plants with purple flowers and white seed coats or white flowers and purple seed coats.

After performing the testcross and collecting 15,206 offspring, you would analyze the phenotypes of the offspring. If you observe a significantly different pattern than what you would expect from the null hypothesis of independent assortment, such as a majority of the offspring having purple flowers and purple seed coats, it would suggest that the wf and sw loci are probably the same, pleiotropic locus.