Case study :The Evolution of Color Vision in Monkeys: From Nucleotides to Ecology

1. Under what circumstances do dichromatic monkeys fi nd more Kix than do trichromatic monkeys?

2. What kind of vision is associated with distinguishing food from non-food by shape or pattern? Explain your
answer.

3. What kind of vision is associated with distinguishing food from non-food by color? Explain your answer.

4. Review slides 26-29 which describe an experiment on how monkeys found food. What was the overall design of the experiment to  determine the importance of pattern/shape in selecting food? What did the results indicate?

5. Evolution question: If being a trichromatic monkey provides richer color cues than being a dichromatic monkey, why are there any dichromats at all?

6. What is the basic pathway for color perception from light to brain?

7. What are cone cells and what is their function in the pathway described for question 1?

8. What is the one entity that varies among the three different kinds of cone cells? What is the nature of this variation?

9. What is the diff erence between medium wavelength (MWS) sensitive and long wavelength (LWS) sensitive receptors/opsins?

10. Why does having three color receptors (a.k.a. opsins) lead to a more complex color perception than just two?

11. What is the relationship between the chromophore (retinal) and the opsin protein of a cone cell?

12. Evolution question: Primates with only two types of opsin protein typically have better low-light vision than those with three opsin  proteins. Th is is because dichromat primates typically have more rod cells than dichromat primates. What are rod cells, how do they work, and under what circumstances could having a high proportion of rod cells be evolutionarily adaptive?

13. How many genes are responsible for trichromatic color vision? What are the genes and proteins involved called?

14. Are all opsin genes located on the same chromosome pair? Explain your answer.

15. How did gene duplication and mutation produce the information for a third type of opsin protein?

16. Explain gene duplication in the X chromosome in terms of meiotic events in an XX (female) individual.

17. How many nucleotides and amino acids do the MWS and LWS genes/proteins have? Why are they so similar?

18. What are the key diff erences between the MWS and LWS genes and proteins? How did these diff erences arise?

19. What is meant by the term "spectral shift"?

20. How do these shifts provide an additional opsin protein for perceiving color?

21. Why do MWS and LWS absorption spectra look so similar?

22. List in bullet form the process of the formation of LWS receptors starting with meiosis.

 23. Evolution question: Variation in populations is an important component of evolution. Explain how each gene duplication and mutation in general can lead to variation in a population for a given characteristic.

24. Was the common ancestor to Old World and New World monkeys likely a di- or trichromat? Explain your answer.

25. When did the split between the two groups occur? What is a reasonable hypothesis for when the gene duplication happened such that a new color receptor could evolve?

26. Explain the presence of a species of trichromatic monkeys in the New World (i.e., the Howler Monkey).

27. Evolution question: How could two populations of one species lead to two diff erent species?