Final answer:
When two white corn progeny, homozygous for a recessive lethal allele (gg), are crossed, all of their progeny will inherit the lethal allele from each parent, resulting in 100% white progeny.
Step-by-step explanation:
When dealing with lethal alleles in corn plants, where crossing two green corn plants results in 2/3 green progeny and 1/3 white progeny, we are observing a scenario where the white color is a result of homozygosity for a recessive lethal allele. The green plants are presumably heterozygous, carrying one lethal allele and one non-lethal allele; thus, when the green plants are crossed (Gg x Gg), the offspring ratio is expected to be 2:1, due to the lethal effect of the homozygous recessive genotype (gg) causing death before the plants can be observed.
If two white progeny are crossed with each other (gg x gg), every offspring they produce will receive a lethal allele from both parents. Therefore, because both parents are gg (homozygous for the lethal allele), all of their progeny will also be gg and hence we would predict 100% white progeny as the result of this cross.