1. The petals of the blue-eyed Mary (Collinsia parviflora) are normally blue. There are color variants of white and pink. Two pure breeding lines, one with pink petals and another with white petals were collected and the following crosses were made, with results shown in the table below: parents F1 F2 blue x white blue 101 blue, 33 white blue x pink blue 192 blue, 63 pink pink x white blue 272 blue, 121 white, 89 pink A. Define the allele symbols that can be used and show the genotype of parents, F1 and F2. B. A cross between a certain blue F2 plant and a certain white F2 plant gave progeny of which 3/8 were blue, 1/8 were pink, and ½ were white. What must the genotypes of these two F2 plants have been?
1. The petals of the blue-eyed Mary (Collinsia parviflora) are normally blue. There are color variants of white and pink. Two pure breeding lines, one with pink petals and another with white petals were collected and the following crosses were made, with results shown in the table below:
| parents | F1 | F2 |
| blue x white | blue | 101 blue, 33 white |
| blue x pink | blue | 192 blue, 63 pink |
| pink x white | blue | 272 blue, 121 white, 89 pink |
A. Define the allele symbols that can be used and show the genotype of parents, F1 and F2.
B. A cross between a certain blue F2 plant and a certain white F2 plant gave progeny of which 3/8 were blue, 1/8 were pink, and ½ were white. What must the genotypes of these two F2 plants have been?
The principle of independent assortment was derived from Mendel’s dihybrid cross experiment. A cross which includes the analysis of two independent characters is called as dihybrid cross. According to this principle, the assortment of genes of one pair is independent of the other pair at the time of gamete formation. So, each pair of opposite traits behaves independently and is not associated with a particular trait. Therefore, new combinations of traits are produced in the offspring. With complete dominance, a self-fertilized dihybrid cross gives a 9:3:3:1 phenotypic ratio in its F2 progenies, and in F1 progeny all with dominant phenotype.
From the first two crosses, both the F1 progenies are blue, which implies that blue is dominant to both white and pink petal color in blue-eyed Mary. Though the F2 generation for the first two cross resembles like that of a monohybrid cross phenotypic ratio but in the third cross, the F2 phenotypic ratio deviates from the Mendelian dihybrid cross 9:3:3:1 phenotypic ratio and all the F1 progeny is blue, which implies that there is more than one gene responsible for the petal coloration.
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