Question

De Vries’ Oenothera lamarckiana was
A) Complex heterozygote with anomalous chromosome behavior.
B) Homozygous with a fragile chromosome.
C) Heterozygote which developed gene mutations.
D) Homozygous with stable chromosomes.

Answer 1

De Vries’ gave mutation theory, which states that new species arise from the pre-existing ones in a single generation by the sudden appearance of marked discontinuous, inheritable, genetic variations called mutations.

Complete answer:
De Vries’ experiment on a plant called Oenothera lamarckiana (Evening Primrose).

Option A: When Oenothera lamarckiana was self-pollinated and its seeds were allowed to grow, the majority of F1 plants were similar to the parents, but a few were different plants. The same results were found in the F2 generation. It suggested that the origin of species is through sudden, large changes of traits from another species and these sudden changes are due to mutation. Later on, it was revealed that most of the variants isolated from Oenothera lamarckiana were due to its anomalous chromosome behaviour i.e., chromosome forms multiple rings at meiosis and chromosomal end segments only involves in recombination (low-level crossing over) and plant shows complex heterozygosity i.e., during meiosis maternal and paternal chromosomes are arranged in alternate order. Therefore, this is the correct option.
Option B: Oenothera lamarckiana showed complex heterozygote with anomalous chromosome behavior. Therefore, this is an incorrect option.
Option C: Heterozygous refers to having inherited different forms of a particular gene from each parent. Oenothera lamarckiana showed complex heterozygotes with anomalous chromosome behavior. Therefore, this is an incorrect option.
Option D: Homozygous is a genetic condition where an individual inherits the same alleles of a gene from both the parents. Therefore, this is an incorrect option.

Thus, the correct option is (A) Complex heterozygote with anomalous chromosome behavior.

Note: Oenothera lamarckiana has 14 chromosomes and the mutants produced from it have 16, 20, 22, 24, 28 and 30 chromosomes. This shows that the mutants are independent species.