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GENETIC VARIATION (GENE POOL
A gene pool is the number of alleles present…
GENETIC VARIATION
GENE POOL
A gene pool is the number of alleles present in a population.
ALLELE FREQUENCY
Allele frequency is the number of times an allele occurs within a population.
GENETIC DRIFT
Genetic Drift is any random change to the allele frequency of a population which could happen by chance.
Genetic Drift has a much greater effect on the allele frequency of smaller populations compared to a larger population.
FOUNDER EFFECT
The founder effect is when a small number of an original population leaven and form an entirely new population. the allele frequency is unlikely to be a fair representative of the original gene pool.
BOTTLENECK EFFECT
Bottleneck effect is the sudden mass loss of numbers due to human and/or environmental effects such as a tsunami, earthquakes. The allele frequency is unlikely to be a fair representative of the original gene pool (parental population).
INBREEDING
Inbreeding occurs when closely related individuals produce offspring together.
It usually reduces the biological fitness of a population,
It is more likely that both carry recessive alleles for the same even/trait. Therefore, their offspring are much more likely to inherit tow non-functional alleles for the same trait. This could lead to the result in disorders that reduce biological fitness.
NATURAL SELECTION
Natural Selection is the process by which individuals with the fittest characteristics/alleles to cope, better survive in a changing environment and reproduce to pass on the favourable alleles to the next generation.
SEXUAL SELECTION
Most individuals don't mate randomly since they'd rather mate more often with a close neighbour or mates that are similar to them. However, there are other individuals who carefully choose a mate that has desirable traits (adaptations). By doing so, there is greater chance for offspring to inherit these traits which increases chance of survival.
ARTIFICIAL SELECTION
Artificial Selection or selective breeding, involves breeding individuals with the most desirable phenotypes.
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GENE FLOW AND SPECIATION
Gene flow is the movement of genes into or out of a population which involves immigration (when new individuals enter the population) and emigration (when individuals leave the population) and the pollution may lose or gain alleles through this.
Gene flow can have a greater effect on smaller populations since some individuals might be the only ones to carry a particular gene.
Speciation is the process when if two populations are isolated from one another and there is no gene flow between the two populations, then they may develop into two distinct species.
MUTATION
A mutation is a random, spontaneous, permanent change in the sequence of DNA or number of chormosomes.
CHROMOSOMAL MUTATIONS
Chromosomal Mutations occur as a result of errors in crossing over during meiosis and affect large segments of DNA containing many genes. Types of this are Deletions, Translocation, Duplication and Inversion.
GAMETIC VS SOMATIC MUTATIONS
Mutations in the gametic cells can be inherited by the offspring since it is a genetic mutation.
However, mutations in somatic cells cannot be inherited since the cause could be from the environment and so forth.
GENE MUTATIONS
Gene mutations alter the sequence of bases in a single gene such as if a new nucleotide has been added (Base Insertion), if a nucleotide as been removed (base deletion) or if a nucleotide has been swapped or replaced (base substitution).
MUTAGENS
Mutagens are environmental factors that induce a change in the base sequence of an individual's DNA.
Common Mutagens are chemicals (benzoyl peroxide, cigarettes), radiation(uv rays, x-rays), viruses (cancer, HPV) and other microorganisms.
MEIOSIS
Meiosis is a type of cell division that produces four daughter cells that each have a set of unique combinations of alleles (genetically different), as well as, half the original number of chromosomes from the parent cell. Meiosis takes place in sex organs (testes/ovaries).
PURPOSE OF MEIOSIS
The purpose of meiosis is to produce gametes (sex cells) such as sperm cells and egg cells.
The cell divides into two again which results in four daughter cells that each have half the number of the original number chromosomes and each also have a unique set of alleles with each created gamete having only one allele of each gene which can be different from the parent gamete (segregation).
Once the parent cells divides into two, the chromosomes line up independently and randomly at the equator and get pulled apart.
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Then, the spindle network of fibres pull and split the chromosomes apart and the parent cell starts dividing into two.
The homologous pairs then line up randomly and independently in the equator of the cell, this is called Independent Assortment. The spindle networks of fibres begin to form and attach to the homologous pairs.
Next, the chromosomes swap and exchange a section of DNA which form new combinations of alleles. This process is called Crossing Over.
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is when the chromosomes in the parent cell are condensed and not clearly visible but unwind as strings of DNA.
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LINKED GENES
Link genes are genes that are on the same chromosome and often move together during meiosis because they are physically tethered together.
Therefore, independent assortment does not affect linked genes since it only alters the combination of chromosomes and not the combination of alleles but Crossing Over does.
This is why linked genes are more likely to reduce variation depending on how close the genes are to one another in the same chromosome. This is because if the linked genes are closer together, then they are more likely to cross and exchange together during Crossing over, so there is not much variation.
GENE
A gene is a section of DNA that codes for a specific trait or characteristic.
ALLELES
Alleles are different forms of the same gene.
GENOTYPE
Genotype is the set of alleles of an organism
PHENOTYPE
Phenotype is the physical expression or characteristics coded by the genotype.
LETHAL ALLELES
Lethal Alleles are recessive that causes severe disabilities or even death.
Someone can get the lethal allele if both parents are carries of the recessive lethal allele.
COMPLETE/INCOMPLETE/CO DOMINANCE
Complete Dominance is when one allele is dominant and is fully expressed by the phenotype of the organism.
Incomplete Dominance is when neither of the two alleles are dominant and is expressed as a combination of both dominant and recessive alleles (the characteristics are mixed).
Co-Dominance is when both alleles are dominant and are both expressed independently (the characteristics don't mix).
MULTIPLE ALLELES
Multiple alleles occurs particularly in blood types and these alleles cannot be represented with just one letter.
There are different versions of the gene that code for this surface carbohydrate. These three alleles cannot be represented by a single letter and are thus denoted, A, B, and O. The alleles A and B code for different carbohydrate groups, while O codes for no carbohydrate.
Therefore, O is known as the recessive allele.
TEST CROSS
Test Cross is used to identify if an organism is a Homozygous Dominant, Homozygous Recessive or Heterozygous.
To get a reliable result from a test cross, you may need to produce a large number of offspring.
VARIATION
Variation is the characteristics (phenotype) of individuals within a population that results both genetic and environmental influences.
It is an advantage because by having variation within a population, some individual will better adapt and survive so they can pass on those genes to the next generation, leading to an evolutionary change.