Variation in gene numbers among eukaryotes
Gene numbers in
various organisms remind us that evolution is not
necessarily progressive. Single-celled yeasts have
smaller numbers of genes than do multi-cellular
organisms, but invertebrates such as flies
and worms do not vary greatly from humans.
The higher number of genes in flowering angiosperms
reflect additional metabolic functions (including photosynthesis)
with respect to animals. The exceptionally high number
in maize is likely due to its origin as a
cultivated polyploid species that has become
partially diploidized through divergence of
duplicated gene loci. Compare this table with the chart
of C-value [total
DNA content].