Introduction

Sexual reproduction was an early evolutionary innovation after the appearance of eukaryotic cells. It appears to have been very successful because most eukaryotes are able to reproduce sexually, and in many animals, it is the only mode of reproduction. And yet, scientists recognize some real disadvantages to sexual reproduction.

On the surface, creating offspring that are genetic clones of the parent appears to be a better system. If the parent organism is successfully occupying a habitat, offspring with the same traits would be similarly successful. There is also the obvious benefit to an organism that can produce offspring whenever circumstances are favorable by asexual budding, fragmentation, or asexual eggs. These methods of reproduction do not require another organism of the opposite sex. Indeed, some organisms that lead a solitary lifestyle have retained the ability to reproduce asexually. In addition, in asexual populations, every individual is capable of reproduction. In sexual populations, the males are not producing the offspring themselves, so in theory an asexual population could grow twice as fast.

However, multicellular organisms that exclusively depend on asexual reproduction are exceedingly rare. Why is sexuality (and meiosis) so common? This is one of the important questions in biology and has been the focus of much research beginning in the latter half of the twentieth century. There are several possible explanations, one of which is that the variation that sexual reproduction creates among offspring is very important to the survival and reproduction of the population. Thus, on average, a sexually reproducing population will leave more descendants than an otherwise similar asexually reproducing population. The only source of variation in asexual organisms is mutation. This is the ultimate source of variation in sexual organisms, but in addition, those different mutations are continually reshuffled from one generation to the next when different parents combine their unique genomes and the genes are mixed into different combinations by crossovers during prophase I and random assortment at metaphase I.

For homework this week, you will watch a film that explores the evolutionary benefits of sexual reproduction. During the film please write down the answers to the questions in the attached worksheet. You will submit this before your lab section meets, instead of completing a quiz. During next week’s lab, be prepared to discuss the film in class.

1. What is special about the lizards being rounded up in Texas?
2. Name three drawbacks to sexual reproduction:
3. Which fish had more parasites?
4. Why are the sexual fish considered a harder target for the parasites?
5. What happened to the sexual fish after many died from drought?
6. What happened to the sexual fish once new minnows were added to the pool?
7. Why do females produce few eggs?
8. What are 3 problems caused by a peacock’s large tail?
9. What are two traits that peahens look for in peacocks?
10. What advantage does monogamy give females?
11. What advantage does monogamy give males?
12. What is the major difference between chimpanzees and bonobos?
13. Why do female chimpanzees mate with as many males as possible?
14. How are female bonobos different from female chimps?
15. According to the study, what do females look for in a short-term mate?
16. What seems to influence what features a female finds more attractive?
17. Why, according to the narrator, are humans unique?

Lab worksheet:

If your lab section did not complete the nutrition activity last week, the version of the worksheet below includes the section on nutrition: