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For Evidence for Evolution

Guided Reading Chapter 24

1. Define the following terms:

a. Speciation-- The origin of a new species in evolution.

b. Anagenesis--
AKA phyletic evolution – it’s the accumulation of changes that gradually a given species into a new species with different characteristics

c. Cladogenesis--
AKA branching evolution- it is the splitting of a gene pool into two or more separate pools, which each give rise to one or more new species

2. What is the biological species concept?

They define species as a population or group of populations whose members have the potential to interbreed in nature and produce fertile offspring but are unable to produce offspring with those in other populations. They are linked by who they can reproduce with.


3. What are the differences between prezygotic and postzygotic barriers to reproduction?.
Prezygotic barriers to reproduction impede mating or hinder fertilization. Postzygotic barriers to reproduction prevent an organism from developing and/or reproducing.
-Sawyer W & Steph A

4. Identify each of the following as prezygotic or postzygotic barriers and write a brief definition of each:

Habitat isolation -
Prezygotic barrier – two populations occupy different habitats

Temporal isolation: Prezygotic barrier – two populations mate at different times of the day, month, season or year
Behavioral isolation: Prezygotic barrier – sexual competition limits chance of mating
Mechanical isolation: Prezygotic barrier – sex organs are incompatiblec110694_02_14a-peacock.jpg
Gametic isolation: Prezygotic barrier – Sperm cannot fertilize egg
Reduced hybrid viability: Postzygotic barrier – genes from parents interact and do not mix
Reduced hybrid fertility: Postzygotic barrier – chromosomes from parents do not match up
Hybrid breakdown: Postzygotic barrier - some first gen hybrids are fertile but cannot mate with original species


-Sawyer W & Steph A

5. Detail these other definitions of species:

a. Morphological species concept
-Characterizes a species by its body shape, size, and other structural features. It applied to asexual and sexual organisms and can be useful without the information on gene flow.

b. Paleontological species concept
-Focuses on morphologically discrete species known only from the fossil record. Many species are forced to be identified this way because there is little to know information on their mating abilities.

c. Ecological species concept
-Views a species in terms of its ecological niche, its role in a biological community. An example is two finches; they look the same but are different in what they eat.

d. Phylogenetic species concept
-Defines a species as a set of organisms with a unique genetic history; as one branch on the tree of life. Biologists trace the phylogenetic history of a species by comparing its physical characteristics or its molecular sequences with those of other organisms.

external image 2z6cxsy.jpg

Adam A, Mario C, Martin A

6. What is the basis for allopatric speciation?
Gene flow is interrupted by when a population is geographically isolated. An example would be a lake partially drying up. This would split the lake in two. The two populations would become separate species. Martin A.

-When gene flow is interrupted in a population and it is divided into geographically isolated subpopulations. Then one or both of the populations may undergo evolutionary change during the period of separation. For instance, when a lake is divided into smaller lakes, the water level of the larger lake drops dramatically. Adam A, Mario C, Martin A
external image Speciation%20Diagram.png

7. What does sympatric speciation mean?
external image SymptrcSpctnSml.jpg
Sympatric speciation is the developing of new species in geographically overlapping populations. The speciation occurs when a mutation, or certain mating, occurs that creates genetic polymorphisms. It does not necessarily create phenotypic polymorphisms. After many generations, the polymorphism begins to create different organisms that look and act slightly differently than the original species, eventually creating a whole new species.
-Steve W.-

8. What is the difference between autopolyploidy and allopolyploidy?

9. In what types of organisms are polyploidy speciation more common and why do you think this occurs?
Polyploidy speciation is more common in plants because they reproduce much differently than animals. Their pollen is carried from one plant to another in order to reproduce, so two species of plants accdiently mating in not as uncommon as it is in animals. Accidents in cell divison occur more frequently in plants and tetraploids are able to mate and with other tetraploids much easier. Also, plants are able to become asexual when a hybrid is infertile, which animals are not able to do. Since the hybrid cannot proudce sexually, the offspring is able to evolve quickly into an asexual organism in able to survive.

external image flower.gifexternal image beeonmum.jpg

10. What is adaptive radiation and why do island chains tend to be discussed often with this topic?
Adaptive radiation is evolution of many diversely adapted species from common ancestor. Island chains are discussed with this topic because islands are areas where much allopatric speciation occurs. Many island species tend to float, fly, or blow over to seas to mainland or to different areas on the island. As one population gives rise to a new species, and members of those species make their way to neighboring islands and so on. Many new species are formed with new characteristics enabling them to survive in diffferent habitats. These places across island are still closely located, however, and some species make it back to the original species and they are able to coexist with their common ancestors because they still have similar traits.

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?

Gradualisms is when species descended from a common ancestor gradually diverge more and more in their morphology as they acquire unique adaptations, where punctuated equilibrium changes mostly as it buds from a parent species and then changes little for the rest of its existence. As the species diverge through the evolution sequence it is possible that a parent species could diverge and enter a stage of gradualism. No, one does not have to exclude the other.


12. Define the following terms:
a. Heterochrony

An evolutionary change in the rate or timing of developmental events.
b. Allometric growth
It is the proportioning that helps give a body its specific form
c. Paedomorphosis
It is when reproductive development accelerates compared to somatic development, the sexually mature stage of a species may retain body features that were juvenile structures in an ancestral species
d. Homeotic genes
They determine such basic features as where a pair of wings and a pair of legs will develop on a bird or how a plant’s flowers parts are arranged

13. What impact have the Hox genes had on vertebrates?
The Hox genes have had a great impact on vertebrates because they have introduced positional information to animal embryos. In some vertebrates transformed from aquatic to land animals by not prompting the development of the correct structures needed for swimming and slowly, the mechanisms needed to live on land developed. -- The red team

14. How does the evolution of the horse exemplify the concept that evolution is driven by the interactions of the organism and its environment?
Upon a look at all lines to the modern horse, it is clear that not all developments leaned toward less toes, bigger bodies, and teeth for grazing; rather each member of the line was simply adapted to its present environment and did not adapt based on a goal of what the horse should become. -- The red team