Concept explainers
Figure 8.9 In pea plants, round peas (R) are dominant to wrinkled peas (r). You do a test cross between a pea plant with wrinkled peas (genotype rr) and a plant of unknown genotype that has round peas. You end up with three plants, all which have round peas. From this data, can you tell if the parent plant is homozygous dominant or heterozygous?
To analyze:
If the parent plant is homozygous dominant or heterozygous.
Introduction:
An organism is known as homozygous dominant when it carries two copies of same dominant allele and when it carries two copies of the same recessive allele, then it is called as homozygous recessive. In case of heterozygous organisms, two different alleles of a gene are present.
Explanation of Solution
Given:
According to the figure, Punnet square depicts the cross between plants with yellow and green seeds. There is a cross between the true-breeding parent (P) plantswhich produce F1 heterozygotes and are capable of self-fertilization. This self-cross of the F1 generation can be used for analysis with the Punnet square for predicting the genotype of the F2 generation. If the inheritance pattern of the dominant and recessive is provided then, the genotypic and phenotypic ratios can be determined.
Here, the pea plants having round peas(R) are dominant to the wrinkled peas(r). A test cross between a pea plant with the wrinkled peas having genotype (rr) and an unknown genotype having round peas. The progenyhas three plants with round peas. From this data,it cannot be surely concluded if the given plant is homozygous or heterozygous because the data set given is quite small. Due to a random chance, the three plants have acquired the dominant gene only even if the recessive gene is present.
Thus,from this data, we can't conclude if the given plant is homozygous or heterozygous because the data set given is quite small.
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