Final answer:
In interspecific hybridization between two grass species with diploid numbers of 8 and 10, endoreduplication results in a fertile hybrid with a doubled chromosome number, which is 16. This happens because the chromosome doubling provides each chromosome with a partner, allowing meiosis to proceed normally. The correct option is d).
Step-by-step explanation:
Polyploidy and Chromosome Numbers in Plant Hybrids
When interspecific hybridization occurs between two species of grass with a diploid chromosome number of 8 and 10 respectively, and sterile hybrids result, a process called endoreduplication (also known as chromosome doubling) can overcome this sterility.
Endoreduplication involves the replication of chromosomes in the cell without cell division, leading to a doubling of the chromosome number. This process generates fertile hybrids with an even number of chromosomes, which is viable for plant species, as they can be more robust and larger.
For instance, in the case of wheat, emmer wheat and einkhorn wheat underwent similar processes to create new plant species with higher ploidy levels.
When considering the diploid numbers of the two grass species in the question (8 and 10), after endoreduplication in the sterile hybrid, the chromosome number would double.
As such, the option that represents the chromosome number of a fertile hybrid through endoreduplication, when starting with one set of 8 and one set of 10 chromosomes would be d) 16 chromosomes. This doubling creates a situation where meiosis can proceed normally due to each chromosome having a pair. Option d) is the correct one.