Period+2+GR+24


 * AP Biology**
 * Guided Reading Chapter 24**

1.Define the following terms: beal. . . good! a.Speciation ​origin of species

b.Anagenesis accumulation of changes that gradually transform a given species into a species with different characteristics

c.Cladogenesis splitting of a gene pool into 2 or more separate pools, which give rise to 1 or more new species

2.What is the biological species concept? beal. . . good!

population or group of populations whose members have the potential to interbreed in nature and produce fertile offspring with members of other populations

3.What are the differences between prezygotic and postzygotic barriers to reproduction? beal. . . good!

​ Prezygotic barriers prevent mating or hinder fertilization if mating occurs. These barriers include habitat, temporal, behavioral, mechanical, gametic isolation. Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult. Examples are reduced hybrid viability, reduced hybrid fertility, and hybrid breakdown.

4.Identify each of the following as prezygotic or postzygotic barriers and write a brief definition of each: beal. . . good except for H!


 * a.****Habitat isolation:** Prezygotic; species are seperated by different habitats so they do not mate.


 * b.****Temporal isolation:** Prezygotic; species that breed during different times of day, seasons, or years cannot mix genes.


 * c.****Behavioral isolation:** Prezygotic; courtship rituals for mating or other behaviors unique to species can be reproductive barriers.


 * d.****Mechanical isolation:** Prezygotic; morphological differences prevent mating.


 * e.****Gametic isolation:** Prezygotic; sperm of one species may not be able to fertilize the eggs.


 * f.****Reduced hybrid viability:** Postzygotic; the genes of different parent species may interact and impair the hybrid's development.


 * g.****Reduced hybrid fertility:** Postzygotic; sterile hybrid Chromosomes of parents differ in number or structure.


 * h.****Hybrid breakdown:** Postzygotic; first generation beal. . .is a hybrid is fertile and viable but as generations go on the feebleness decreases. beal. . . increases!

5.Detail these other definitions of species: beal. . . good!

a.Morphological species concept- Characterizes species by its body shape, size, and other structural features

b.Paleontological species concept- Focus on morphologically discrete species from fossil record

c.Ecological species concept- Views species in terms of its ecological niche

d.Phylogenetic species concept- Defines species as a set of organisms with a uniques genetic history

6.What is the basis for allopatric speciation? beal. . . good!

Allopatric speciation occurs due to geograhical barriers. This is when the gene flow of a population is interrupted when a population is divided into geographically isolated subpopulations. For instance, when a lake is divided into smaller lakes, the water level of the larger lake drops dramatically.

 7. What does sympatric speciation mean? beal. . . good!

**Sympatric speciation is a mode of speciation occuring as a result of a radical change in the genome of a subpopulation, reproductively isolating the subpopulation from the parent population.**

8.What is the difference between autopolyploidy and allopolyploidy? beal. . . good!

**Autopolyploidy is when an individual has more that 2 chromosome sets, all derived from a single species.**  **Allopolyploidy is when a common type of polyploid species resulting from 2 different species resulting interbreeding and combining their chromosomes.**

9.In what types of organisms are polyploidy speciation more common and why do you think this occurs? beal. . . plants!

Polyploidy occurs when two species interbreed and produce a hybrid. Two species such as a horse and donkey have a different number of chromosome pairs, and when they breed a chromosome will be left over the offspring making it sterile.

10. What is adaptive radiation and why do island chains tend to be discussed often with this topic? beal. . . good!

Adaptive radiation is the emergence of numerous species from a common ancestor introduced into a new environment and are presented with new oppurtunities and challenges. It happens more often on islands because speices mover from their current environment and relocate to one that has not been established as a new environment.

11.Compare and contrast the models of punctuated equilibrium to gradualism as models for the rate of evolution. Does one have to exclude the other?​ Punctuated equilibrium shows a more direct evolution, applied quick and obvious. On the other hand, the gradualism model is more spread out and shows a more gradual rate of eveolution. Because these two models are so different one of them usually does exclude the other one. Often, punctuated equilibrium completely erases gradualism.

beal. . . good!

12.Define the following terms: beal. . . good!
a.Heterochrony Heterochrony is evolutionary change in the timing or rate of an organism’s development. b.Allometric growth The variation in the relative rates of growth of various parts of the body, which helps shape the organism. c.Paedomorphosis The retention in an adult organism of the juvenile features of its evolutionary ancestors. d.Homeotic genes Any of the genes that control the overall body plan of animals and plants by controlling the developmental fate of groups of cells.

13.What impact have the //Hox// genes had on vertebrates? beal. . . good. . . fins to limbs! Over the course of evolution, the Hox genes, genes that control the positioning of structures such as arms and legs, have duplicated multiple times, from very simple invertebrates with only one copy of the gene, to simple semi vertebrates with two copies of the gene, with more defined structures than the previous invertebrates, to modern vertebrates like us, with four copies of the gene, with complex, clearly defined structures like arms and mouths. in vertebrates, the hox genes not only allow us to have a spine, but the define the positioning of individual structures. The positions where the hox genes are expressed in fetal developement are the positions where our bodies grow, which in turn leads to the creation of limbs, and in complex vertebrates, fingers, the extremeites of extremeties.

14.How does the evolution of the horse exemplify the concept that evolution is driven by the interactions of the organism and its environment? The modern horses ancient ancestors were small, four-toed browsers, animals that browsed around in the brush, eating leaves and the like off of bushes and low tree branches. Modern horses clearly have only one toe on each foot,are very large, and are grazers, anmals that eat grass. These evolutionary changes did not occur wih he end goal of creating a modern horse, but instead to better adapt the animal to its changing circumstances, which eventually led to the horse. a trend that leads soley to modertn horses may be readily apparent if you are to follow only the line linking horses to their ancestors, Hyracotherium, but by following all of the various evolutionary destinations of this animal, this trend dissappears quickly. The family tree of the horse is long and varied, with many independent branches leading to many different ends,many of which were not one toed, were not grazers, which is a relativley modern trait, and were of various sizes, with the modern horse being merely the only surviving example of such a branch. Thus it is evident that evolution had no set goal, but meandered around untl it reached its modern state.

beal. . . good!