Speciation - level 3

Evidence for evolution

-fossils
-homologous structures
-analogous structures
-vestigial structures
-biogeography
-genetic analysis

Parallel evolution

When two or more related groups evolve among similar lines. just independently from one another.

Coevolution

In which a feature of one speices acts as a selection pressure for another species.

What is the importance of genetic variation?

It increases the chance that some individuals will have an allele or trait suited to a change in environment or selection pressure, increasing the chance of survival of the population.

Independent assortment

occurs during metaphase 1 and is when the chromosomes line up randomly along the equator of the cell so the chromosomes are randomly divide in anaphase 1.

Crossing over

When chromosomes exchange segments of dna at a locus, resulting in a new combination of alleles on each chromatid - occurs during prophase 1.

Segregation

When the chromosomes line up randomly, single file and the chromatids separate randomly so that each gamete receives a single copy of each allele, resulting in unique allele combinations.

Define mutation and explain its importance

a permanent change in the base sequence of DNA.
A mutation is the only form of new alleles.
mutations are the only form of variation which can occur during mitosis.

Harmful mutation

mutation results in a trait which prevents reproduction and/or survival until reproductive age. the mutation will be selected against and will be less likely to be established in the gene pool.

Silent mutation

Provides neither an advantage or disadvantage towards survival or reproduction.

Beneficial mutation

Mutation results in a trait which will increase chance of survival or reproduction so will be selected for and trait will have an increased presents in the gene pool over many generations.

Gene flow

Is the change in allele type and frequency within a population over time.

Genetic drift

Describes the change in allele frequency or allele type due to chance events rather than selection pressures.

Founder effect

Occurs when a small number of individuals emigrate from a population or become geographically isolated from their original population.

Bottleneck effect

When a population's numbers decline drastically due to a random catastrophic event.

What are the effects of a genetic drift?
- bottleneck and founder effect

So the allele type and frequency likely differ from the orintifal population/ the remaining population is not representative of the whole population's alleles .
- reduction in genetic diversity.

Natural selection

Natural selection occurs when populations are subject to selection pressures. The organism which contains the most favourable allele are more likely to:

- Survive to reproductive age

- Finding a mate and producing offspring → passing on their favourable alleles.

Stabilizing selection

When selective pressure selects against the two extremes of a trait, the median phenotypes become more common.

Disruptive selection

When the selection pressure favours parents at opposite extremes of the rait. Intermediate phenotypes are selected against.

Directional selection

When selective pressure selects against one extreme of the traint, the populations traint distribution shifts towards the other extreme

Dimorphism

When male and females display different physical traits.
- These traits may appear disadvantageous as they make the animals more visible to predators, hinder movements and are energy intensive to grow and maintal so it would be thought that these traits would be naturally selected against.However these traits increase an individual's ability to reproduce

Species

A group of individuals that are able to successfully interbreed and produce fertile offspring, and are reproductively isolated from other species.

Evolution

Evolution is an umbrella word which describes a population's selection for or against specific alleles over time in response to a changing environment.

Cline

Is a pattern of gradual variation between individuals over a geographical area, usually as a result of environmental differences.

Population

Is a group of organisms of a single species, living in the same geographical area.

Deme

Is a subset of a population that has limited gene flow with members of the larger population.

Ring species

When individuals on each end of a cline are unable to breed, however neigbouring clines are able to interbreed allowing gene flow to occur between the whole population.

Speciation

The formation of a new species.

RIM's

Reproductive isolation mechanisms (RMS's) are barriers that prevent one member of a species from mating with different species.

Decribe prezygotic RIM's
- acronym

Occur before the egg is fertilized.
- 6 different types (EGG BMT)

Geographical isolation

Species occur in different areas with no geographical overlap.

Ecological isolation

species occupy different habitats within the same area.

Behavioural isolation

Different courtship rituals, sounds, calls or colouration

Temporal isolation

Activity, mating or flowering occurs at different time of the day, month or year

Mechanical isolation

Reproductive structures are incompatible nd prevent the delivery or acceptance of gametes

Gametic isolation

Gametes are incompatible and unable to fuse and produce a viable zygote.

Postzygotic RIM's
- acronym

If two species manage to overcome prezygotic isolating mechanisms there are many RIM which occur after a zygote has formed.
- h BIS

hybrid breakdown

Hybrids may be viable, fertile and capable of producing offspring.
- There offspring have extreme genetic abnormalities
- Offspring has reduced fitness and fertility

Hybrid inviability

The hybrid embryos are often not viable because the genes of the two species are incompatible.
- The hybrid dies
- Or the hybrid does not reach reproductive age.

Hybrid sterility

Hybrid offspring that do survive birth and reach sexual maturity
- are sterile so cannot produce gametes.

Allopatric speciation

Occurs when two populations become geographically isolated from each other. Continued geographical isolation may lead to reproductive isolation and perhaps ultimately the formation of a new species (speciation).

- Geographical isolation
- Gene pool
- Behavioral isolation
- Reproductive isolation
- Competition

Sympatric speciation

Is the formation of a new species without geographical isolation. The new species become reproductively isolated even though they are surrounded by their parent population.
- Occurs mostly in plants through polyploidy.
- may occur in animals to reduce intraspecific competition within a population.

What results in instant speciation?

Polyploidy

Polyploidy

Is caused by errors during cell division that result in the cell having more than two copies of each chromosome (>2n). The resulting organism is genetically and thus reproductively unique (creating a new species).
- However this is not necessary a problem in plant species because they can carry both male and female sex organs and can thus reproduce through self fertilization.

Autopolyploidy

Occurs when the spindle fibers fail to separate (nondisjunction) during anaphase 1 resulting in non-reduced diploid gametes instead of haploid games.
- If these diploid gametes fuse with a normal haploid gamete during fertilization, the result will be a triploid organism (3 sets of chromosomes).
- If the diploid gamete fuses with another diploid gamete (potentially self fertilization) the resulting zygote will be tetraploid.

Allopolyploid

Is the process where two different species produce an infertile hybrid. The two parent chromosomes are not identical.
Typically non identical chromosomes cannot pair up during meiosis. As a result the hybrids are sterile.
However if the germinal cells in the new hybrid species undergo chromosome doubling (autopolyploidy) then the meiosis can occur usually.
- When this happens the hybrid species will be able to produce fertile gametes that obtain chromosomes from both paternal species.

Aneupolyploidy

Is the process where an individual inherits one, two or less chromosome/s. This mechanism is usually the result of a failure of chromosomes to seperate(Non-disjuction)
during meiosis.
Most individuals are infertile because the chromosomes are unable to pair properly during meiosis.

Genome duplication

an event which creates an organism with additional copies of the genome or set of all DNA.
-Aneupolyploidy can be overcome by genome duplication, enabling individuals to become fertile.

Non-disjuction

a failure of chromosome pairs to separate properly during cell division resulting in an imbalance of chromosomes in daughter cells

Monosomy

Chromosomal abnormality consisting of the absence of one chromosome from the normal diploid number

Trisomy

a condition in which an extra copy of a chromosome is present in the cell nuclei, causing developmental abnormalities.

Advantages of polyploidy

- More chromosomes so larger cell nuclei → larger cells → larger leaves, stems, fruits, flowers etc.
- May allow plants to grow in a wider array of habitats and be more resistant to pests and diseases

Disadvantages of polyploidy

- If a plant contains an uneven number of chromosomes they will be sterile, so resulting fruits will be seedless.

Evidence of evolution acronym

Fossil Evidence
Biogeography (species distribution)
Comparative anatomy
Comparative embryology
Genetic Evidence
Biochemical Evidence

Genetic evidence

Comparison of genetic sequences between two species.

Biochemical evidence

Comparison of the amino acid sequence or protein structure between two species.

Comparative embryology

Is the comparison of embryos between different species.

Fossils

Are the preserved remains of organisms which have been buried in sediment and imprinted into casts or molds.

Biogeography

The study of the geographic distribution of species across the planet and through geological time shows a distinctive pattern.

Comparative anatomy

Is the comparison of body structures in different species

homologous structures

- Occurs through the evolution of species into many other species
- The ancestral and modern species will have similar structures but these structures may take on different functions/ adapted for a different purpose for different species to suit their specific selection pressures.

Analogus structures

Describes how unrelated species may have similar traits or functions even when they are not from the same heritage. Analogous structures evolve because the species will have similar selection pressures and fill - similar ecological roles.
Similar selection pressures → The same adaptations are favoured → beneficial adaptations have survival advantage.
- May indicate convergent evolution

Vestigal structures

Decibels tissues, bones or organs which are functionless to an organism. These structures are the remains of features that served an important function in ancestral species.

Nucleotide sequence

Includes analysis and comparison of the nucleotide sequence of a particular gene. The number of differences (mutations) can be considered a measure of time.
- If the nucleotides of two species are very different from one another (they contain my mutations) it is likely that they did not share a recent common ancestor because mutations take a long time to accumulate.
- If two species have a very similar nucleotide sequence for the same gene then it is likely that they shared a recent common ancestor.

mtDNA analysis

Mitrondra contains their own DNA; since mitochondria are found outside of the nucleus, they are not subject to meiosis.
- The only form of genetic variation of mDNA is through mutations.
- Mutations accumulate at a fairly constant rate
- Thus the number of mutations present in the mtDNA is proportional to the time since divergence of the two organisms.
-Sperm cells do not pass on any mtDNA so all mtDNA passed onto sons or daughters comes from the ovum.

Y chromosome

Due to the difference in size between the y and the x chromosomes, during meiosis t can only exchange alleles from the very tips (pseudoautosomal regions) of the chromosome
- 95% of the Y chromosome is conserved and passed on from father to son
- Any changes that occur are due to mutations which occur at a consistent rate and can be traced back to their origin.

Divergent evolution

An ancestral population divided into two or more increasingly distinct species
- Occurs when gene flow between populations is blocked resulting in the accumulation of different characteristics though natural selection
- Homologous structures are evidence for divergent evolution

adaptive radiation

Is a type of divergent evolution which describes the process of a large number of new species evolving in a relatively short amount of time from a common ancestor.
- Usually occurs following a major tectonic process, natural disaster, extension events or colonisation of a new unexplored habitat.
- As new neiches become available the population adapts to fill the new habitat and poteintaily form new species.

convergent evolution

Similar traits arise in two or more unrelated species.
- Occurs because the species are reacting to similar selection pressures. These similar niches which they fill in their uiue environment cause similar problems requiring similar solutions
- Analogous structures are evidence of convergent evolution.

Coevolution

Describes an evolutionary relationship between unrelated species which occupy the same environment but different niches in that environment.
- One species develops an adaptive advantage → acts as a selection pressure against another species → triggering the other species to naturally select for another charistic which reduces the effect of the selection pressure → this change may then cause another evolutionary change in species 1.
- This relationship can also be mutualistic where the two species benefit from the relationship.

gradualism (rate of speciation)

When evolutionary change occurs gradually over a long period of time.
- Accumulation of change due to natural selection, at a fairly constant rate until the species is considered a unique species.
- Fossil records contain many transitional forms.

puncuated equilibrium (rate of speciation)

When evolutionary change occur rapidly
Species are 'punctuated' by periods of rapid evolution after long periods of relative stability.
- Occurs as a result of a rapidly changing environment where new niches are created or populations become geographically or reproductively isolated
- The sudden appearance of species in the fossil record would support this.

Phylogenetic tree

Diagram that depicts the lines of evolutionary descent of different species, organisms, or genes from a common ancestor.

Genetic distance

Measure of the genetic divergence between species or between populations within a species.

Immigration

When new individuals enter the population.

Emigration

When individuals leave the population.

Gene pool

A gene pool is the sum total of the genes (and their alleles) present in a population.

Allele frequency

A measure of how common a certain allele is in the population.

Genetic equilibrium and factors that affect allele frequency

• Genetic Drift
• Natural Selection
• Artificial Selection
• Sexual Selection
• Gene Flow (Immigration & Emigration)
• Mutations
• Founder Effect
• Population Bottlenecks

Artifical selection

Selection by humans for breeding of useful traits from the natural variation among different organisms

Sexual selection

A form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates.

Mutations

Random errors in gene replication that lead to a change in the sequence of DNA. Has the potential to lose function/characteristic.

Selection pressures

Are external agents which affect an organism's ability to survive in a given environment. Selection pressures can be negative (decreases the occurrence of a trait) or positive (increases the proportion of a trait)

Sexual demorphism

the distinction in appearance of male and female organisms. Can be size differance, adornment, color etc.

Inbreeding

A selective breeding method in which two individuals with identical or similar sets of alleles are crossed.(Offspring has the potential to be affected by a recessive disorder)

Variation

Variation in the features (phenotypes) of individuals within a population is the result of both genetic and environmental influences.

Non-heritable variation

This variation is responsible for any acquired differences in the phenotypes of individuals in a population. These differences are usually the result of environmental influences or the actions of individuals.

What is an advatage of genetic variation?

Individuals are better adapted to their environment than others. Others who are less adapted are less likely to survive and reproduce, leading to speciation---evolution.

What are the different types of environmental changes?

Changes in climate
The introduction of a new predator
Changes in prey / availability of different food sources
Disease (the emergence of a new disease or strain)

What are key points to evolution?

-Evolution does not occur within a single generation. No individuals can "adapt" to their environment.
-Only large groups (populations) can evolve adaptations over long periods of time (many generations).
-No one can chose or try to adapt. It's purely up to chance whether or not an individual has inherited a combination of adaptations that will help them survive and reproduce.

Instant speciation

Is the production of a single individual (or the offspring of a single mating) that is reproductively isolated from the species to which the parental stock belongs and that is reproductively and ecologically capable of establishing a new species population.

Selection pressure

When environmental factors such as predation, herbivorism .etc. affect the survival of a species.