Please enable JavaScript.
Coggle requires JavaScript to display documents.
Evolution, image, image - Coggle Diagram
Evolution
GENETIC DRIFT
FOUNDER EFFECT
Small number of individuals establish a new population. Founders carry some, but not all, of the alleles from the original population. By chance, an allele that was common in the large population might be uncommon or a rare allele might be much more common in the new population.
BOTTLENECK EFFECT
Bottlenecks result in a loss of genetic diversity following an extreme reduction in the size of a population. Natural disasters, disease, and human activities can quickly reduce the size of a large population. Survivors will have only a fraction of the alleles and therefore gene pool diversity will be lost.
GENE FLOW (MIGRATION)
The movement of genes from one population to another. Can change gene frequencies in either population or both through the movement of genes.
GENE FREQUENCY
Factors that affect gene frequency: mutations, natural selection, sexual selection, genetic drift, gene flow.
SPEICATION
-
The formation of new species from existing species. Can result from natural selection acting on multiple heritable traits over time. Two populations may become reproductively isolated over time and become two species if there is little of no gene flow between them.
Allopatric Speciation: the formation of a new species as a result of evolutionary changes following a period of geographic isolation.
Sympatric Speciation: the evolution of populations within th same geographic area into separate species.
-
Changes to allele frequency as a result of chance. The smaller the population the greater the influence of genetic drift. Occurs in all populations of size, but its effects are strongest in small populations. May result in the loss of some alleles, including beneficial ones. Can have major effects when a population is sharply reduced in size by a natural disaster or when a small group splits off from the main population to found a colony. Most populations are large enough that the effects of genetic drift are small.
MUTATIONS
A mutation is a DNA copying error that occurs during DNA replication (interphase). Mutations are found in both meiosis and mitosis. If the occur during meiosis, the mutation can be passed down on to the next genereation.
Two common mutations are the deletion of genes and the duplication of genes and they usually occur during crossover in meiosis. Examples: Cystic fibrosis (3 nucleotide deletion in CFTR gene), Huntingtons disease (3 nucleotide repeat in the HTT gene), and Duchenne muscular dystrophy (deletion of part of the DMD gene, x-linked inheritance)
Deleted genes can result in low chance of survival however duplicated genes are often viable and can be beneficial (gene duplication is often the source of new genes). The extra copy is free to mutate and gain a new function.
COMMON ANCESTRY
FOSSIL RECORD
Fossils found in young layers of rock are much more similar to species alive today, as fossils appear in chronological order in the rock layers.
Transitional Fossils: show intermediary links between groups of organisms and link the part with the present.
Evidence for Common Ancestry: Fossils, anatomy, embryos, and DNA sequences provide corroborative lines of evidence about common ancestry, with more closely related organisms having more characteristics in common.
DNA codes for proteins. Collectively, proteins are responsible for an organisms traits. DNA underlies the similarities and differences in fossils, anatomy, and embryos. More closely related organisms have more genes in common.
-
-
PHYLOGENETIC TREES
Phylogenetic trees are used in hypothesising about common ancestry based on several lines of evidence. Similarities among living things might indicate relatedness. Organisms with the most similarities tend to be more closely related. 
SELECTION
NATURAL SELECTION
The way in which nature favours the reproductive success of some individuals within a population over others.
Selective pressures may result from any number of abiotic or biotic factors such as disease, climatic conditions, food availability, or predators.
STABILIZING SELECTION
The average phenotype within a population is favoured by the environment. Selective pressures reduce the reproductive success of individuals that exhibit extreme phenotypes.
-
SEXUAL SELECTION
Favouring of any trait that specifically enhances the mating success of an individual (traits indicate health -- good genes). Often leads to males and females of a species evolving appearances and behaviours that are quite different from each other (dimorphism). Examples: Colourful birds, song, dance. Dependent on the female choice who is the influencer and results in male to male competition.
DIRECTIONAL SELECTION
Favours individuals with a more extreme variation of a trait. The result is a shift away from the average condition
ARTIFICIAL SELECTION
Selective breeding: directed breeding where humans breed individuals that exhibit a particular trait. For example: domestication of dogs, selection of fruits/vegetables, breeding of cattle.
Variation: different traits (fur, colour, texture, demeanour, heightened senses, etc). Heritable: Some traits are passed on from one generation to the next. Selection: humans have selected desirable traits.
-
If an individual has an advantageous trait it is more likely to reproduce. Since traits are passed from parents to offspring, offspring are likely to inherit advantageous traits. Over time advantageous traits become more common in a population.
-
HUMAN EVOLUTION
HOMO SAPIENS
Homo sapiens, the first modern humans, evolved from their early hominid predecessors between 200,000 and 300,000 years ago. The first modern humans began moving outside of Africa starting about 70,000 - 100,000 years ago.
Human lineage diverged from that of apes at least seven million years ago. Homo sapiens are part of a group called hominids, which were the earliest human-like creatures. Though there was a degree of diversity among the hominid family, they all shared the trait of bipedalism.
All Humans living today descended from ancestors living in Africa. Migration predicted to have taken place around 100 000 years ago. Homo sapiens were not the only ones to migrate out of Africa though. Homo erectus migrated approximately 1.9 million years ago but disappeared around 130 000 years ago. There were also Neanderthals which migrated approximately 500 000 years ago and disappeared approximately 30 000 years ago.
Humans and Neanderthals share about 99.7% of their DNA and we shared a common ancestor about 500 000 years ago. Neanderthals are not our direct ancestors -- they are a sister species and recent evidence suggests that there was some interbreeding.
-
-
-
-