Question

Some inbred strains of the weedy plant Arabidopsis thaliana flower early in the growing season, but other strains flower at later times. Four different Arabdiposis plants (1–4) were crossed, and the resulting progeny were tabulated as follows: Mating Progeny 1 × 2 77 late : 81 early 1 × 3 134 late 1 × 4 93 late : 32 early 2 × 3 111 late 2 × 4 65 late : 61 early 3 × 4 126 late a. Explain the genetic basis for the difference in flowering time. How do you know that among this group of plants, the flowering time trait is influenced by the action of a single gene? Which allele is dominant and which recessive? b. Ascribe genotypes to the four plants. c. What kinds of progeny would you expect if you allowed plants 1–4 to self-fertilize, and in what ratios?

Answer 1

The difference in flowering time in Arabidopsis thaliana is influenced by a single gene, with a dominant late flowering allele and a recessive early flowering allele. Self-fertilization of the plants would result in different progeny ratios depending on the genotypes of the plants.

Step-by-step explanation:

The difference in flowering time in different strains of Arabidopsis thaliana is influenced by a single gene. This is supported by the fact that when four different plants were crossed, the resulting progeny showed consistent ratios of late to early flowering. If the trait was influenced by multiple genes, the ratios would vary.

In this case, the late flowering allele is dominant, while the early flowering allele is recessive. This is evident from the progeny ratios observed in the different cross combinations.

If plants 1-4 were allowed to self-fertilize, the expected progeny ratios would depend on the genotypes of the plants. If plants 1, 2, and 4 were heterozygous for the flowering time gene (Late/Early), the expected ratio of late to early flowering progeny would be 1:2:1. If plant 3 was homozygous for the late flowering allele, all its progeny would be late flowering.

Answer 2

a. Let us consider that L is responsible for late and l is responsible for early. From the mentioned data, it can be concluded that allele L or late is dominant over early. By crossing plants 1 and 4 we get the expected ratio of 3: 1, which shows that it follows Mendel's law of dominant.

b. The genotype of all the four plants are:

1st plant = Ll

2nd plant = ll

3rd plant = LL

4th plant = Ll

c. If the plant 1 is self-fertilized then the expected progeny will be 3 (late): 1 (early).

In case if the 2nd plant is self-fertilized, the expected progeny will be only early.

In case if the 3rd plant is self-fertilized, the expected progeny will be only late.

In case if the 4th plant is self-fertilized, the expected progeny will be 3 (late): 1 (early).