Presentation to species and Speciation .pptx

Species concept and Speciation mechanism

1. Forces of evolution

2. Introduction evolution is a change in the allele frequencies in a population over time Allele frequencies is the ratio, or percentage, of one allele to the other alleles for that gene within the given population.

3. According to the Hardy-Weinberg principle genetic variance in a population will remain stable across generations. Allele frequencies and genotype frequencies stay stable but some “forces of evolution”, which cause deviation of such frequency from the theorem the forces that includes : mutation, gene flow, genetic drift, and natural selection

4. Mutuation Mutation, an alteration in the genetic material Mutation is the original source of all the genetic variation found in every living being. The majority of mutations exist in somatic cells, These mutations will not be passed on to future generations and therefore do not affect the population over time Only mutations that occur in the gametes, will be inherited by future generations.

5. Types of mutuation A point mutation is a single-nucleotide change in the genetic code resulting in the substitution of one nucleic acid base for a different one It's effect may be major or minor, or may make no difference at all . An example of point mutation is sickle cell anaemia. It involves mutation in a single base pair in the beta-globin chain of haemoglobin pigment of the blood. Glutamic acid in short arm of chromosome II gets replaced with valine at the sixth position.

6. Crossover events involve the swapping of DNA between homologous chromosomes during meiosis I, potentially creating new combinations of alleles on a single chromosome.

7. Nondisjunction events, on the other hand, happen when chromosomes or chromatids fail to separate properly, resulting in an abnormal number of chromosomes in the daughter cells.

8. Genetic drift specifically is the random shift in allele frequencies from one generation to the next genetic drift is simply the result of chance. It occurs when certain individuals have more offspring than others, not because of any genetic advantage, but because of random factors such as being in the right place at the right time. The occurrence of genetic drift is more pronounced in small populations. In contrast, large populations are less affected by chance and are. In a small population, it is possible for the next generation to have different allele

9. The bottleneck effect happens when a population undergoes a drastic reduction in size, leading to a loss of genetic diversity.

10. The founder effect, on the other hand, occurs when a small group of individuals establishes a new population, resulting in a limited gene pool. founder effect is closely associated with the concept of inbreeding, which involves the selection of mates exclusively from within a small, closed population with limited genetic variability. This can occur in physically isolated populations or due to cultural practices that restrict mate selection to a small group

11. Gene flow Gene flow refers to the movement of alleles from one population to another.Such movement may be due to migration of individual organisms that reproduce in their new populations, or to the movement of gametes (e.g., as a consequence of pollen transfer among plants)
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12. The level of gene flow between populations greatly depend on the type of organism. Lower gene flow rates are observed in populations of relatively stationary organisms, which are more isolated from one another compared to highly mobile organisms. For example, wind-pollinated crops like corn may have limited fertilization beyond 50 feet or 0.0152 kilometre

13. organisms with higher gene flow rates can disperse their genes over longer distances. For instance, fruit flies released in Death Valley were found almost 15 kilometers away from the release site

14. Natural selection occurs when certain phenotypes provide an advantage or disadvantage in survival and/or reproductive success. This means when there are differences in fitness among members of a population As a result, some individuals pass more genes to the next generation. This causes allele frequencies to change.

15. The following conditions are required for the natural selection to occur: There must be a variation among individuals within a population in some trait. This variation is heritable (i.e., there is a genetic basis to the variation, such that offspring tend to resemble their parents in this trait). Variation in this trait is associated with variation in fitness

16. Natural selection can be classified as directional, balancing/stabilizing, or disruptive/diversifying, depending on how the pressure is applied to the population

17. Directional selection In directional selection one extreme of the phenotype range is selected for, in an area with dark trees covered, natural selection select dark moths over lighter ones .

18. Disruptive selection This is when two or more extreme phenotypes are selected for. For example, if there is an area with dark trees covered in areas of light lichen, natural selection will favour two types of moth - those with lots of melanin, which will camouflage against the dark trees, but also the type with very little melanin, which will camouflage against the light coloured lichen . Moths with intermediate melanism will be selected against as they will not be successfully camouflaged in either environment .

19. Stabilising selection - an average phenotype is selected for and extremes of the phenotype are selected against . In an area where trees were less dark, and where there was less light lichen, moths at either extreme of colouration would be less successfully camouflaged and would be selected against. Moths with intermediate melanism would be selected for.

20. Sexual selection is a component of natural selection that targets reproductive success, rather than mere survival. It favors traits that enhance the chances of attracting a mate. In some cases, these traits that are sexually appealing may even pose higher risks in terms of survival.
A classic example of sexual selection involves the brightly colored feathers of the peacock peahens generally prefer males with the most vibrant and full tails. these extravagant tails offer a reproductive advantage

21. Conclusion
Various evolutionary mechanisms lead to genetic diversity within a population. Natural selection operates by favoring alleles that provide advantageous characteristics or behaviors, while discouraging those that are harmful. Genetic drift arises from the random chance that certain individuals in the gene pool produce more offspring than others. Changes in allele frequencies can occur when individuals enter or leave the population due to gene flow. Mutations in an individual's DNA can introduce new variations into a population.

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