Upon
completing his initial series of experiments, Mendel redirected his focus
toward a new inquiry. His aim was to investigate the inheritance of two traits
concurrently. To achieve this, he chose a pea plant yielding round, yellow
seeds and another plant yielding wrinkled, green seeds. The first-generation
(F1) seeds all exhibited roundness and yellowness, which indicated the
dominance of these traits. Mendel's F2 generation, consisting of 556 seeds,
yielded the following counts: 315 round yellow, 108 round green, 101 wrinkled
yellow, and 32 wrinkled green seeds. Notably, the F2 generation's outcomes
replicated those of the parental traits – round yellow, wrinkled green – while
also introducing combinations like wrinkled yellow and round green. This occurrence
indicated a recombination event, signifying the emergence of novel gene
assortments. Mendel duly observed that the offspring materialized in a ratio of
9:3:3:1.
These
findings laid the foundation for Mendel's second overarching deduction: the law
of independent assortment. This principle posits that "when a pair of
contrasting characters are crossed, the characters are inherited or assorted
independently of each other."
Drawing
from the conclusions regarding the inheritance of individual traits, we
ascertain that in the F2 generation, the probabilities of yellow seeds are 3/4,
green seeds are 1/4, round seeds are 3/4, and wrinkled seeds are 1/4. By
multiplying these independent probabilities of seed shape and color, we arrive
at the frequency of seed types within the F2 generation.
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| Dihybrid Cross |
Drawing
from the conclusions regarding the inheritance of individual traits, we
ascertain that in the F2 generation, the probabilities of yellow seeds are 3/4,
green seeds are 1/4, round seeds are 3/4, and wrinkled seeds are 1/4. By
multiplying these independent probabilities of seed shape and color, we arrive
at the frequency of seed types within the F2 generation.
