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How species evolved.
| Term | Definition |
|---|---|
| Gene pool | A gene pool refers to all genes and alleles present within a particular population or species. |
| Allele frequencies | Refer to the proportion of a particular allele appearing at a certain genus locus in a gene pool. |
| Allele frequency calculations | = 2 (number of homozygotes) + (number of heterozygotes) ------------------------------------------------------------------------- total number of individuals |
| Homozygotes | Have to copies of the allele |
| Heterozygotes | only have one copy of the allele |
| Mutations | All genetic variations between species and individuals of the same species is a result of a mutation. Mutations are changes to DNA. Mutations can have beneficial, harmful or no effect at all. |
| When mutations occur | Mutations can occur randomly during replication. They occur spontaneously or as a result of mutagens - factors that induce mutation. |
| What to mutations affect | Mutations may affect a single gene, multiple genes or may involve entire chromosomes. |
| What do common mutagens include | They include different forms of radiation. |
| Somatic mutations | Occur in body cells & only affect that individual. These mutations are heritable because they affect gametes & therefore be passed onto offspring. Germ-line mutation may bring a new allele into a gene pool, potentially influencing the allele frequencies |
| Point mutations | A mutation that alters, adds or removes a single nucleotide from a sequence of DNA or RNA. These include; Substitution mutations and Frameshift mutations |
| Substitution mutations | Point mutation in which one nucleotide is replaced by another type of nucleotide. The different types if substitution mutations include: Silent mutation, Missense mutation, and Nonsense mutation. |
| Silent mutation | Involves a substitution that results in no change in the amino acid. As the triplet genetic code is redundant, more than one code encodes for the same amino acid. The redundancy is the third nucleotide. |
| Missense mutation | Point mutation involving substitution that results in an amino acid replacement. The impact of this type of mutation on the characteristic (phenotype) of the organism depends upon importance of the affected amino acid to the function of the protein. |
| Nonsense mutation | Mutations result in the generation of a 'stop' codon & no further amino acids are added after the site of mutation, such as UAU(tyrosine) to UAA(STOP). These mutations stop translation & can have serious effects, particularly if it occurs early in a gene. |
| Frameshift mutations | Involve two -more nucleotides being added removed from a nucleotide sequence, altering every codon in that sequence from that point onwards. Have significant effects on the polypeptide because as soon as every codon is altered so too is every amino acid. |
| What is the result of Frameshift mutations | The loss of functional protein, as it is likely that the resulting polypeptide would be completely different. In cases where the frameshift mutation creates a STOP codon earlier in the sequence, the resulting polypeptide will be shorter. |
| Block mutations | Affect large sections of a chromosome, typically multiple genes. These types if mutations usually occur during meiosis in eukaryotic cells. they can be caused by mutagens such as radiation. When a gene is disrupted by the mutation, effects are serious. |
| Duplication mutations | Part of a chromosome is copied. There can be thousands of repeats. This often increases gene expression, which can be harmful or beneficial depending in the gene involved. Block mutation |
| Deletion mutations | Remove sections of a chromosome. Deletion lead to disrupted or missing genes, which can have serious effects on growth and development. Chromosomal deletions are often fatal. Block mutations. |
| Inversion mutations | During an inversion mutation, a section of the sequence breaks off the chromosome, rotates 180˚ and reattaches to the same chromosome. Inversions may involve as few as two bases or they may involve several genes. Block mutations |
| Translocation Mutations | Segments of two chromosomes are exchanged. For example, sections from two non-homologous chromosomes may break off at the same time. They may reattach to the other chromosome, swapping genetic material. Block mutation. |
| Where natural variation exists | In a population through mutations that may have created new alleles or by different allele combinations in sexual reproduction. |
| Selection pressure | A factor in an organisms environment that removes unsuited individuals, and are therefore alleles from the gene pool. Act on phenotypes. Can be natural environment pressures or artificial pressures brought by humans through selective breeding. |
| Examples of environment selection pressure | - Climatic conditions such as extreme temperature changes and drought. - Competition for resources such as the availability of food and water, as well as competition for shelter - Mate availability - Predator abundance |
| What natural selection refers to | To environmental selective agents acting on a wild population whereby individuals with one phenotype in a population are more likely to survive and reproduce than other varieties, thus increasing the allele frequency in gene pool. |
| Process of natural selection for exam (steps 1,2,3) | - The variation of _ already exists in the _population - Presence of an environment selection pressure. - Individuals with advantageous phenotype more likely to survive & produce viable offspring, passing alleles for the favourable trait onto offspring. |
| Process of natural selection for exam (step 4) | - Over generations the allele frequency and therefore number of individuals in he population with favourable trait increases. |
| Variation | Individuals in a population vary genetically, which leads to phenotypic differences. |
| Selective advantage | Individuals with phenotypes that are fitter or more advantageous under the environmental selection pressure are conferred a selective advantage, allowing them to survive and reproduce more successfully. |
| Heritability | The advantageous trait must be heritable, allowing it to be passed on from the parents to their offspring. Therefore, over time, the frequency of the advantageous allele will increase. |
| Effect of selection pressures on genetic diversity | Reduce the genetic diversity of a gene pool as the fitter individuals with alleles that code for advantageous phenotypes are more likely to survive and reproduce. |
| Genetic drift | The random changes to allele frequencies in a gene pool as a result of chance events, resulting in a reduction in genetic diversity. |
| Where is genetic drift more clearly seen | In small populations with little-no gene flow, the random death of individual can significantly alter allele frequencies. The few survivors that reproduce to give the next generation may by chance be an unrepresentative sample of the original population |
| When does genetic drift occur | When populations decrease for a period of time (bottleneck effect) or in small founding populations (the founder effect). |
| Bottleneck effect | Results in drastic reduction in population size caused by chance event like natural disaster & allele frequencies may change, reducing genetic diversity. Survivors reproduce to give next generation may be unrepresentative sample of original population. |
| Founder effect | Occurs when a small group of individuals from a larger population move to a new location and establish a new population. The allele frequency of the founding individuals is unlikely to be a representative sample of the original population. Reduction. |
| Major risks of reductions in genetic diversity | Inbreeding - Keeps harmful alleles in the gene pool - Lower adaptive potential - populations become vulnerable to new selection pressures that could challenge and potentially wipe out the entire population due to the absence of advantageous alleles. |
| Gene flow | The movement of alleles through genetic exchange between individuals of different populations, resulting in an increase in genetic diversity. |
| Migration | Mvmt one population to another. Individuals migrate into a population mate w/ local members, bringing particular genetic traits into population. Plants gene flow results from movement of seeds & pollen dispersed tra populations by wind, water & animals. |
| The effect of gene flow on genetic diversity | Immigration and emigration can both affect allele frequencies. When new alleles are brought into a population through immigration, genetic diversity in a population increases. |
| The effect of gene flow on genetic diversity pt 2 | Increase is more pronounced in smaller populations since they have a smaller gene pool to begin with. In larger populations, the immigration of new alleles into the population does not significantly affect the gene pool. |
| Emigration | Removes alleles from a population's gene pool, decreasing genetic diversity. Once again, the effects of emigration are more pronounced in smaller populations compared to larger populations. |
| Mechanism : Genetic drift | Bottleneck effect and founder effect, the effect on genetic diversity is decrease for both |
| Mechanism : Gene flow | Immigration - Increase, Emigration - Decrease, Interbreeding - increase |
| Speciation | The process when populations genetically diverge until they become distinct species. When genetic differences accumulate, through processes such as mutations, natural selection, genetic drift & gene flow, speciation can occur. Formation of new species. |
| Categories of Speciation | Allopatric speciation or sympatric speciation. Speciation is the evolution of new species from an ancestral species. |
| Allopatric speciation | Allopatric speciation occurs when a population becomes divided by a geographical barrier. Isolation prevents individuals of the separated sub-populations from interbreeding (prevention of gene flow) |
| What populations may be subject to | Seperate populations may be subject to different selecting agents because they exist in different environmental conditions. |
| What genetic drift may produce | Genetic drift may produce different changes in each population by chance. Different new alleles may be generated in each gene pool as a result of mutation. |
| Process of allopatric speciation for exam | - Population is separated, no gene flow (due to geographical barrier) - Accumulation of differences due to mutations occurring independently in populations. |
| Process of allopatric speciation for exam pt 2 | - Each population experiences different selection pressure through natural selection individuals with (Suitable characteristics for the different environments survive and reproduce). Brought back together, unable to produce viable/fertile offspring. |
| Sympatric speciation | Involves the formation of a new species in populations located in the same geographical location. Doesn't rely on the presence of a geographical barrier preventing gene flow. |
| Sympatric speciation pt 2 | Different selection pressures act on different phenotypes within a pop causing individuals with certain phenotypes into diverge from others and form a new species. |
| Sympatric speciation pt 3 | Can arise from genetic abnormalities that occur during gamete formation, producing polypoid variants, which involve differences in the number of sets of chromosomes compared to the original parent. |
| Selective breeding | The process by which humans decide which individuals may breed and leave offspring to the next generation is called artificial selection or selective breeding. |
| Selective breeding pt 2 | Humans choose individual organisms with desirable traits and deliberately interbreed them to increase the allele frequency of those desired traits in the gene pool. Allows certain extreme forms to reproduce, preventing others from reproducing |
| Steps that apply to all forms of selective breeding | 1 Determine the desired trait 2 Interbreed parents who show the desired trait 3 Select the offspring with best form of the trait and interbreed these offspring 4 Continue this process until the population reliably reproduces the desired trait. |
| Increases and decreases Selective breeding | Also decreases the frequency of all other alleles for this trait. Reduces genetic variation within the gene pool. furthermore, genes do not |
Created by:
Laura.s