Evolution, 4th Edition

160 CHAPTER 6

different animals independently evolve similar coloration, is that the result of

changes at the same or at different genes? Surprisingly, the evolution of darker

and lighter colors in many species of mammals, birds, and reptiles is often due

to changes at just a single locus, the melanocortin-1 receptor, or Mc1r. The protein

produced by this gene regulates the production of pigments in hair, feathers, and

scales. Mutations at several different nucleotides in the Mc1r gene have produced

dark (melanic) coloration (FIGURE 6.29). Here parallel phenotypic evolution results

from genetic changes that are parallel at the level of the gene but not at the level of

the nucleotides.

FIGURE 6.29 Diagram of the melanocortinin-1 receptor bound to the cell mem-

brane. The arrows point to positions where selection has changed amino acids to

produce new coloration in four species of animals. In these cases, the results are

polymorphisms within species (shown in the photos). Many other polymorphisms

within species and differences between species have also evolved by changes to

the Mc1r gene. (After [36].)

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_06.29.ai Date 11-10-2016 01-13-2017

Membrane

Extracellular

Cytoplasm

NH 2

Snow goose Jaguar

Rock pocket mouse

Striped whiptail

COOH

Amino

acids

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