Hybrids formed by mating two different species are often incapable of reproducing successfully with each other or with the members of their parent populations. Explain why this is the case. (Hint: Consider what you know about chromosome numbers and meiosis.)

Because of presence of different sets of chromosomes in hybrids

Explanation:

In normal animals the body cells have two sets of chromosomes out of which one comes from mother and the other from father. During the gamete formation, when meiosis occurs, these two sets of chromosomes are duplicated and then only one set of chromosome is transferred to each of the four formed gametes. Now each of these cells have only one set of chromosomes which is a mixture of mother and father chromosomes. This is possible because the parents have same sets of chromosomes.

But, as the hybrids are formed by mating of two different species parents, the chromosomes of hybrids don't match up with others in the order and during meiosis and thus the pairing between the chromosomes become difficult. This is why hybrids are incapable in reproducing sexually.

the missing space is phylum

oxygen = 21% of the atmosphere

nitrogen = 78%

carbon dioxide = 0.1%

argon =0.934%