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Biology Examination Unit 3 - Coggle Diagram
Biology Examination Unit 3
Science Inquiry
Processes for Continuity of Life
DNA Structure and Function
Variation and Mutation
Genetics
Biotechnology - Its tools and techniques
Biotechnology - agriculture and environmental conservation
Evidence for Evolution
Mechanism of Evolution and Speciation
Evolution and its Mechanism
Evolution: process of cumulative, heritable change in a population over many generations.
Theory of evolution: all organisms have developed from previous organisms and that all living things have a common ancestor in some initial form of primitive life.
Mechanisms: cause basis of evolution; changes in allele frequencies within a gene pool.
Mechanism for evolution
Mutation
Define: A source of new alleles in a population's gene pool.
It is a permanent change in DNA sequence of a gene.
Can change one allele into another, but the net effect is a change in frequency of an existing allele.
Change in frequency is small, its effect on evolution is insignificant unless it provides a beneficial trait with a selection pressure in the environment.
Selection pressure: an environmental factor that can be survived by those individuals in a population who possess a beneficial trait, but not others.
SP in an environment:
Presence of food/prey/shelter (resources)
temperature, water availability, pH (abiotic factors)
pathogens/disease + predators (biotic factors)
contributes to changes in allele frequency in a population gene pool
mutation may produce an allele that is selected against, for or neutral.
Example: Peppered moth
white speckled form
dark form
better for evading bird predation. Overtime they will dominate population.
Mutation is ultimate source of variation
Population: group of individuals of the same species that live in the same geographic area and readily interbreed to produce fertile offspring.
Variation: based on differences in DNA sequences, which give rise to different forms of genes (alleles), which turn result in different phenotypes.
Members of population have variation in their genotypes that causes variation in their phenotypes.
Gene pools
Gene: The means of transmitting phenotypes from one generation to another.
many exist in different forms as alleles + characteristics of individuals are determined by alleles they inherit.
this variation causes alleles carried by different individuals that leads to most of variation in a population.
Define: Total collection of alleles within a population.
meiosis
crossing over
independent assortment
non-disjunction
chemical agents
Natural Selection
Occurs when selection pressures in the environment confer a selective advantage over a specific phenotype to enhance its survival and reproduction.
leads to changes in allele frequency in the gene pool of a population
individuals have certain inherited traits are more likely to survive and reproduce at higher rates than other individuals.
Principles:
VARIATION
Individuals in a population differ from one another; that is, individuals within populations show variation.
Due to mutation in alleles and meiosis/sexual reproduction processes.
Include:
crossing over
independent assortment
random fertilisation
random mating
OVERPRODUCTION
There are more individuals produced in a population than the environment can support.
Environmental resources are limited.
Not all individuals can survive to reproduce.
COMPETITION AND SURVIVAL OF THE FITTEST
Environmental selection pressures e.g. food availability, predators + diseases favour those with advantageous traits/alleles.
Leads to competition between individuals in a population, and those with the advantageous trait may outcompete those w/o advantageous trait.
Known as: survival of the fittest
Those who are more fit are better suited to the environment in which the population lives.
HIGHER REPRODUCTIVE RATE
Individuals with inheritable advantageous trait are more likely to surivive, reproduce and have higher reproductive rate than those w/o.
HERITABILITY
advantageous alleles are passed down to offspring (e.g. camouflaged colouration)
ALLELE FREQUENCY CHANGE
Over consecutive generations, frequency of advantageous alleles/traits increases.
Frequency of disadvantageous traits decreases.
Overtime, advantageous allele = fixed; frequency can become 100%.
Disadvantageous allele = extinct, frequency becomes 0%
Example: GIRAFFES
Variation
Were alleles for short and long necked giraffes due to mutation and sexual reproduction processes.
Overproduction
More giraffes are produced than environmental resources can sustain.
Not enough leaves to feed a whole population, and last leaves to be eaten = high up.
Competition and Survival of the Fittest
Individuals compete for the leaves high in the tree.
Only those with the advantageous tall allele/trait can reach and consume enough food.
Higher productive rate
Individuals who possess the advantageous allele can survive and have a higher reproductive who do not possess advantageous allele.
Heritability
Giraffes with higher reproductive rate = likely to pass their inheritable, advantageous allele on to offspring.
Allele Frequencies Change over Generations
Next generation of giraffes have a higher frequency of advantageous (tall) alleles. Over many generations tall allele accumulates until allele = fixed and disadvantageous short allele = extinct.
First proposed by Charles Darwin
Idea: Populations typically produce more offspring than the surrounding environment support. As a result, there is competition for survival.
Genetic Drift (Found in short-answer, MC or EXT resp)
Bottle-neck effect
major disaster = major decrease in population, few survive
Define: Occurs when there is a disaster that reduces a population to a small handful, which rarely represents actual genetic makeup of initial population.
Founder effect
lots of variation within population
random individuals from large population finds a new area results in new population
small population = genetic drift is more likely.
Define: a few individuals who migrate to new area and become isolated from larger population might not carry al alleles present in original population.
Means isolated population has less genetic diversity > original population
deleterious recessive allele = higher chance of coming together > original population
occurs when there is dramatic decrease in genetic diversity caused via development of small colonies from original population that remain isolated from other colonies.
Only small subset of genetic diversity of source population = likely to be included in new population and relative frequencies of alleles may be very different from what they were in source population.
It is more about random changes
all about chances
Occurs in all population but strongest effect found in smaller populations.
more likely with small population
Definition: Random changes from generation to generation. It is a mechanism of evolution in which allele frequences of a population change over time due to chance
Typically, loss of genetic variation over generations.
Gene Flow
Define: Transfer of alleles and results from migration of individuals from one population to another. Can be due to immigration and emigration.
Frequency of a allele = no. of allele in population / total number of alleles for the gene in the population.
Micro-evolution
Define: A change in the frequencies of various alleles within a population. Which is a change below the species level.
COMPARISON
MICRO:
A change in the frequencies of various alleles within a population
Change below the species level
Small-scale change in the gene pool of a population due to the mechanisms of mutation, natural selection, genetic drift and gene flow.
MACRO:
Changes in allele frequencies in more than one population/species
Large scale change resulting from an accumulation of micro-evolutionary changes over many generations and a long period of time.
Major evolutionary changes above the species level
Macro-evolution
Define: A set of processes that attempt to explain how new species have evolved in such large numbers.
Processes: that work towards macro-evolution
Natural selection favours phenotypes that make the population better adapted to its environment. Over time population change as their gene pools accumulate small changes in response to natural selection. (MICRO-EVOLUTION)
Eventually a population accumulates so many changes that a new species can be identified. This process can lead to speciation, the multiplication of species
Sometimes a rapid series of speciation events leads to the development of a whole collection of new species, or even genera, families, or higher classification groups. (MACRO-EVOLUTION)
Drawbacks
resources of the gene pool of the population
collection of different alleles in a population
reduces gene pool = reduces allele frequency
selective (artificial) breeding
selecting for certain alleles that code for the traits we want.
best individuals are closely related.
less variation
in-breeding
prone to disease or inherited defects.
sexual selection
Lyre birds
Bigger picture of evolution
Speciation
Terminology
SPECIES: A group of organisms that can interbreed to produce viable, fertile offspring and cannot breed with the individuals of another species to produce fertile offspring.
BIOLOGICAL SPECIES CONCEPT: a genetically isolated group with its own gene pool.
MORPHOLOGICAL SPECIES: defines a species by structural features. Individuals of the same species are morphologically similar.
Define: The formation of a new species. It is the process of one species splitting into two or more species.
Example: Galapagos tortoises similar to smaller Chaco tortoise, found in South America, but are completely separate species.
Darwin hypothesis: Tortoises on the islands originally came from the mainland population, but had changed over time to become better suited to the environment of the Galapagos.
Isolating Mechanisms
Define: separate two subgroups of a population and prevent them from producing fertile, viable offspring. These mechanisms can operate before reproduction has occurred or after reproduction.
Organisms become genetically diverse that they form two new species. They are then no longer able to interbreed, even if the populations come back together.
Pre-reproductive Isolating Mechanisms
Define: Biological or ecological mechanisms that prevent organisms from being able to interact to reproduce.
Temporal (time) mechanisms: Individuals breed during different seasons of the year or times of the day
Behavioural mechanisms: individuals have different courtship patterns.
morphological mechanisms: individuals have different reproductive structures.
Example: Periodical cicadas hatch every 17 years; other hatches every 13 years. Lengthy life cycle act to prevent different populations from interbreeding and producing hybrid offspring.
Post-reproductive isolating mechanisms
Define: Do not prevent mating from occurring but they do prevent young from being produced.
Gamete mortality: gametes don't survive
Zygote mortality: zygote forms but doesn't survive
Hybrid Sterility: Adult offspring are formed but are infertile because they are unable to produce viable gametes, usually because of having received a different number or type of chromosomes from each species.
Allopatric
Gene flow is disrupted when populations become physically separated via geographical isolation.
Populations diverge
Due to selection pressures acting on two populations / other random processes e.g. genetic drift
Physical barriers that can separate a sub-population from original population:
water (terrestrial)
land(aquatic)
Mountains
New physical barriers arise due:
continental drift
rising sea levels
climate change
Steps:
subpopulation
isolation via physical barrier
no gene flow
different selection pressures
natural selection
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