Final answer:
The number of genes in animals can vary widely, with humans having about 20,000 to 25,000 genes. A significant portion of an organism's genome is made up of non-coding DNA, and gene count is not always indicative of complexity due to processes like splicing.
Step-by-step explanation:
The number of genes in animals varies significantly across different species. Humans, which are a complex species, have between 20,000 to 25,000 genes. This might seem like a large number, but even simpler species have nearly as many genes. Not all DNA within an organism codes for genes; for humans, only about 25 percent of DNA base pairs are part of genes and their regulatory elements, and within this subset, only two percent actually code for proteins.
Genetic diversity is vast among living organisms due to the differences in genetic composition. Genome size, which includes both coding and non-coding DNA, doesn't always correlate with the gene count. For instance, more than 180 species have had their genomes sequenced, revealing a range of gene counts, such as 1750 genes for Haemophilus influenzae and roughly 25,000 for Arabidopsis thaliana and Homo sapiens.
It's important to note that gene counts alone don't fully represent biological complexity, as processes such as splicing allow a single gene to produce multiple proteins. This contributes to an organism's complexity without the need for additional genes.