Ch. 23.3 Broad Pattern of Evolution

Question 1

Heterochrony

Answer 1

Changes in rate and timing.
Many striking evolutionary transformations are the result of heterochrony, an evolutionary change in the rate or timing of developmental events. For example, and organism’s shape depends in part on the relative growth rates of different body parts during development. Changes to these rates can alter the adult form substantially, as see in the contrasting shapes of human and chimpanzees.

Question 2

Paedomorphosis

Answer 2

Changes in rate and timing.
Heterochrony can also alter the timing of reproductive organs. If the development of reproductive organs accelerates compared to that of other organs, the sexually mature stage of a species may retain body features that were juvenile structures in an ancestral species, an condition called pedomorphosis.

Question 3

Homeotic Genes

Answer 3

Substantial evolutionary changes can also result from alterations in genes that control the spatial organizations of body parts. Master regulatory genes that determine such features as where a pair of wings and legs will develop on a bird or how flower parts are arranged.