1. A biologist collects seeds from a pale yellow sunflower in his back yard. He
ID: 58423 • Letter: 1
Question
1. A biologist collects seeds from a pale yellow sunflower in his back yard. He grows four, to adulthood, in a greenhouse, and bags the flowers so that they are forced to self-fertilize. Asking questions about whether his flower is cross pollinated, he grows all the seeds from each of these four sunflowers and records the results. His results are as follows. All flowers except some of the progeny from the fourth seed have normal petals:
Seed number one. F1 has pale yellow flowers. F2 Progeny are all pale yellow.
Seed number two. F1 has pale yellow flowers. F2 progeny are 73 pale yellow flowers and 27 red flowers.
Seed number three. F1 has dark yellow flowers. F2 progeny are 77 dark yellow flowers and 23 pale yellow flowers.
Seed number four. F1 has dark yellow flowers and normal petals. F2 have 59 dark yellow flowers with normal petals, 21 dark yellow flowers with curled petals, 17 pale yellow flowers with normal petals, and 3 pale yellow flowers with curled petals.
a) Based upon your intuition for the crosses above, how many alleles determine flower color? What is the dominance relationship among them?
b) Regarding flower color and petal shape, how many loci determine this? Diagram the crosses for seed number 4 and show a plausible genetic hypothesis for his results.
Explanation / Answer
The pale yellow is dominant over dark yellow and dark yellow flowers are dominant over dark red flowers. The normal petals are dominant over curled petals. Therefore, the flower color is determined by the three alleles determine the flower color and the dominance relationship is as follows:
Pale yellow > Dark yellow > Dark red yellow
b)
Regarding flower color two loci determines its phenotype and for petal shape only one loci (two alleles) determines its phenotype. The plausible genetic explanation regarding this is, it is an epistatic relationship. Expression one allele mask the phenotype of another allele.
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