What does an organism's genotype describe? the allele combination for a trait
the physical appearance of a trait
the number of alleles on a gene
the number of different traits inherited

the allele combination for a trait

Explanation:

The genotype describes which alleles (versions) of a gene an organism has. Diploid organisms, such as humans, have two copies of each gene. Sometimes these alleles are the same and the individual is h0m0zygous for that gene. If they are different, the individual is heterozygous for that gene.

The physical appearance of a trait is the phenotype.

a community that experiences major changes undergoes progress

stimulus is a change in the environment that causes an organism to react. the response is the reaction to the stimulus. some examples of stimuli for zebras are drought, to many predators, and bad feeding grounds such as dead grass or plants. zebras respond to stimuli just like all other living organisms