Chapter 5 Flashcards
Evolution and biodiversity
Heritable characteristics
characteristics that an organism possesses due to its genetic make-up
Evolution
the change in heritable characteristics of a species over time
Fossil record
provides a record of the order of the changes in certain species over time
- hence, fossil record provides evidence for evolution
How was the fossil record determined?
- geologists interpreted different rock strata in which fossils were found
- dating of those strata allowed chronological ordering and deduction of which organism came first
- later, came radioisotope-dating
- use of radio isotopes, more accurate dating methods became available, supporting chronology of fossils
Selective breeding
- a form of artificial selection
- where humans select animal or plant with the best characteristics to create a breed or plant line that retains these desired characteristics
- it accelerates the evolutionary process, as evolutionary changes become visible in a much shorter time interval than might have occurred through natural selection
NB/ artificial selection can only happen through human intervention
Domestication of animals and evolution
- selective breeding of domesticated animals shows how artificial selection can cause evolution
- all breeds of household dogs today are the products of selective breeding
- original bloodline is from wolf-like animals that were tamed and bred for more docile traits
- when inheritable physical features of domesticated dogs are compared w/ wolves, it’s clear evolution has occurred
- following several generations of selective breeding, domesticated breeds can differ a lot from their wild ancestor
Homologous
refers to something that is similar in position, structure and evolutionary origin, but not necessarily in function
Homologous structures
structures that share the same origin and ancestral form, but not function
- suggests that the species must have had a common ancestor, but they diverged over time to be better adapted to their respective environments
Divergent evolution
- where there’s an accumulation of differences between groups which led to the formation of new species
- there is a shared ancestor, but the end points are two different lines with two structures that have different functions
Divergent evolution of homologous structures
divergent evolution of homologous structures explains the similarities in limb structure of mammals, birds, amphibians and reptiles, even if each of them has a different method of locomotion
Analogous structure
the function may be similar, but there is no similarity in bone structure or common ancestor
Convergent evolution
when organisms that are not closely related evolve similar structures that are used for similar purposes
- structures develop to resemble each other and have the same function
Speciation
process by which new species form
How do species form?
- Physical separation
2. Adaptive radiation
Physical separation and speciation
- separated populations adapt to environment they inhabit
- if they remained isolated over a long period of time, they would become genetically different
- if, by chance, they met with members from original population, they could no longer interbreed to produce fertile offspring
NB/ a group can be said to be of a different species when they can no longer interbreed to produce fertile offspring
Adaptive radiation
a process in which organisms rapidly diverge from the form of the original species into several new forms specialised to make use of different environmental niches
Darwin’s finches
- shows how related populations, isolated from each other due to geographical barriers, change over time to be better adapted to their environment
- Galapagos finches show continuous variation across their geographical range
- Beak sizes gradually get bigger, there is no sudden change from small beaks to large beaks, w/ no intermediate sizes present
- this supports idea of gradual divergence; organisms change through a slow process and may ultimately form new species
- Thus, when all members of related species are compared, they show continuous variation across geographical range
Industrial melanism
- example of how a change in environment can precipitate an evolutionary adaptation - moth, Biston betularia is active at night and roosts during the day
- It rests on trees and uses tree bark covered w/ lichen as camouflage to remain undetected so birds won’t prey on it
In the 19th century, industrial revolution led to widespread burning of fossil fuels to power machinery
- produced large amounts of sulphur dioxide- killed many plants and lichen
- also produced vast quantities of soot which changed colour of the tree bark- result was darker coloured trees
Populations of Biston betularia consist of two main morphs: a darker and a lighter coloured moth
- melanistic morph was better camouflaged in the most industrial areas
- lighter coloured moth was better adapted to non-polluted areas, because trees were still covered in lichen and had little or no soot - making it less visible to predators
- hence, in industrial areas, no. of darker moth increased, and no. of lighter moth declined
- can be explained as lighter peppered moths were easily spotted and eaten while resting on dark and sooty tree barks
- darker peppered moths were well camouflaged in polluted areas and many survived to reproduce
- hence, pollution brought about by industrial revolution acted as a selection pressure that favoured darker moth over lighter moth
Principle of evolution
- evolution concerns interaction of environment and fitness of a population
- If a change in the environment occurs, only best able to adapt individuals will survive
Gene pool
refers to the sum of all genes found in an interbreeding population
- hence, each species has its own gene pool
Bigger gene poole
- means that if conditions change, a species has a better chance of survival
- It also helps to have a large population
- If there is only a small population left, gene pool will also be small
- species will be endangered
Variation
- phenotype of a species is one way to observe certain characteristics, but a lot of variation is invisible
- range of alleles present in a species accounts for variation in the population
- is a good measure of a healthy gene pool
Causes of variation
- Mutation: any change to DNA sequence is classified as a mutation
- It can range from a single base change to removal of one segment of a chromosome - Meiosis: produces gametes w/ unique combinations of alleles, thus increasing genetic variation of individuals within the species.
- Sexual reproduction: combination of gametes results in a zygote that has genes from both of its parents
Asexual reproduction and variation
- Not all species reproduce sexually
- most prokaryotes and some eukaryotes reproduce asexually
- a species reproduces asexually, it produces a clone that is an identical genetic copy of itself
- only way asexual species can increase variation is through mutation