Biology Homework Chapter 13: Population Changes and Microevolution
Textbook assignment: Chapter 13: How Populations Evolve, sections 12-18.
The second half of this chapter covers the way in which natural selection causes variations in populations over time.
- 13.12 Microevolution is a change in the distribution of a particular trait within a population; it occurs as a result of genetic drift, gene flow, mutation, non-random mating, and differential success in reproduction. Populations usually express one trait or gene in several ways; this leads to variation that allows some individuals to survive changes in the environment. Clines are gradual changes in a trait that match changes in the species' habitat.
- 13.13 Natural selection processes determine which variant survives. In the case of bacteria, where we manipulate the population with antibiotics, those bacteria which survive tend to be more resistant to existing antibiotic methods, creating a serious health concern.
- 13.14 Selection can tend to limit variation at the extremes (stabilizing selection), can favor the extremes over the commonest expression if the common form becomes a negative survival factor (diversifying selection), or can favor one extreme over the other (directional selection).
- 13.15 In some species, non-random mating factors which lead a female to chose one male over another as a mate appear to be related to the female's ability to recognize particular traits are associated with overall survivability. Over time, this selective selection may shift the male population in a species to a particular set of traits, while leaving the distribution of the same gene set unshifted in the female population. This may explain why male birds tend to have showier plumage (since these birds attract mates more frequently) than their female counterparts. Another factor that could contribute to less showy female plumage is the relative susceptibility of female birds to prey while nesting; females are more likely to survive if they can camouflage themselves.
- 13.16 Because natural selection favors bacteria that are resistant to antibiotics, the frequency of resistance is increasing, posing health hazards to the human population. Immunizations developed several generations ago are not effective against current strains of diseases like measles and whooping cough.
- 13.17 Some variations don't affect an individual's ability to survive and reproduce; these are considered "neutral" variations. Diploidy enhances expression of hidden traits based on recessive genes. Some traits favor survival if the carrier is homozygous, others heterozygous. Other mechanisms work to balance phenotypical expressions in the population, and so depend on the frequency of expression in the population. Only inheritable genetic traits determine a species' fitness or lack thereof. Mutations in somatic (body) cells do not affect offspring; learned characteristics do not affect offspring genetically.
- 13.18 Natural selection does not result in individuals that are perfectly adapted to their niche, since it must work only with existing traits that often have to answer multiple requirements of the environment, and that environment can change under catastrophic circumstances.
Read the following weblecture before chat: Theory of Evolution, Part 2
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
See if you can put the strata layers in order from the fossil record at the
Fossil Layers game site.
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- Required: Complete the Mastery Exercise with a score of 85% or better.
- Optional: Test yourself with the textbook multiple choice questions and note any that you miss that still don't make sense. Bring questions to chat!
- Go to the Moodle and take the quiz for this chapter.
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
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