Isolating mechanism.pptx
- 1. Isolating mechanisms Dr. Jagadisha T.V., M. Sc., PGDGT., PhD Assistant Professor Department of Life Sciences (Genetics) Kristu Jayanti college Ph.-No: 8892698143/9449442521, E-mail:jagadisha.tv@kristujayanti.com ORCID ID: https://orcid.org/0000-0002-0596-7830 Research Gate Profile: https://www.researchgate.net/profile/Jagadish-T-V
- 2. Isolation • Any external or internal barrier, that prevents interbreeding between populations, is called isolation. • As a result, the population of a species is either separated into smaller units or the exchange of genes (gene flow) between them is prevented
- 3. • -Isolation is the separation of the population of a particular species into smaller units which prevents interbreeding between them. • -Some barrier that prevents gene flow or exchange of genes between isolated populations is called isolating mechanism. • -A number of isolating mechanisms are operated in nature and therefore divergence and speciation may occur. • -The isolating mechanism is of two types namely geographical isolation and reproductive isolation. Isolation Mechanism
- 4. • The reproductive characteristics that prevent interbreeding between different species • They are important for maintaining the biological species concept, which defines species by reproductive isolation • There are different types of isolating mechanisms, such as • Geographical • Reproductive Isolating mechanisms
- 7. Geographic isolation • Physical separation of populations of organisms from one another due to geographical barriers.
- 8. Geographical Isolation • The separation of species by physical barriers like water forms, oceans, mountains, etc. • The organisms are ultimately separated from exchanging genetic material with other organisms of the same species • As there are fewer chances for variations to occur, new species are not formed in asexually reproducing individuals undergoing geographic isolation • This type of isolation can lead to the development of distinct genetic and physical characteristics in different populations, and ultimately, the evolution of new species
- 9. I. GEOGRAPHICAL ISOLATION • It is also called as physical isolation. • it occurs when an original population is divided into two or more groups by geographical barriers such as river, ocean, mountain, glacier etc. • -these are barriers prevent interbreeding between isolated groups.-The separated groups are exposed to different types of environmental factors and they Requires new traits by mutation. • •The separated Population develop distinct gene pool and they do not interbreed. Thus new spacies have been formed by geographical isolation e.g Darwin's finches Original population
- 12. • An earthquake causes two populations to become separate from each other. • Over time, each species experiences genetic makeup specific only to their own smaller, less diverse populations.
- 13. Reproductive isolation The inability of a species to breed successfully with related species due to • Geographical • Behavioral • Physiological or • Genetic barriers or differences
- 17. Reproductive isolation • is a key concept in evolutionary biology, referring to the mechanisms that prevent different species from interbreeding or producing viable and fertile offspring when they do attempt to mate. • There are several types of reproductive isolation, and they can be categorized into two main groups • : prezygotic barriers and postzygotic barriers.
- 23. 1. Prezygotic barriers 1. Temporal Isolation: 2. Habitat Isolation: 3. Behavioral Isolation 4. Mechanical Isolation: 5. Gametic Isolation: 6. Ethological Isolation:
- 24. 1. Postzygotic barriers 1. Gametic mortality 2. Zygotic mortality 3. Hybrid inviability 4. Hybrid sterility 5. Hybrid breakdown
- 30. Temporal isolation • A type of reproductive isolation mechanism among sexual organisms in which the differences in the timing of critical reproductive events prevent members of closely related species
- 34. courtship is the period wherein some couples get to know each other prior to a possible marriage or committed romantic, de facto relationship
- 39. 1. Prezygotic Barriers: • These barriers occur before the formation of a zygote (fertilized egg). • a. Geographic Isolation: • Populations are separated by geographic barriers such as mountains, rivers, or oceans. Over time, this can lead to the development of distinct species. Example: The Galápagos finches, where different species evolved on different islands due to geographic isolation. • b. Temporal Isolation: • Species may have different mating seasons or times of day when they are active, preventing them from encountering each other for mating. Example: Two species of frogs, one that breeds in the spring and another in the summer, do not interbreed.
- 40. c. Behavioral Isolation: Species have different courtship rituals, behaviors, or signals that prevent them from mating with individuals of other species. Example: Male fireflies use specific light patterns to attract females of their own species; if the pattern is not matched, mating does not occur. d. Mechanical Isolation: The reproductive organs of two species are structurally incompatible, making it physically impossible for them to mate. Example: Some species of snails have shells that coil in different directions, preventing them from mating. e. Gametic Isolation: Even if mating occurs, the sperm of one species may not be able to fertilize the egg of another species due to differences in gametes (sperm and egg) or their chemical compatibility. Example: Sea urchin sperm may not successfully fertilize the eggs of a different species due to gametic differences.
- 47. Gametic Mortality Gametic mortality refers to the death or failure of reproductive cells (gametes) before they can successfully fertilize and contribute to the formation of a new organism. Gametes are specialized cells involved in sexual reproduction: sperm in males and eggs (ova) in females. Gametic mortality can occur for various reasons, including Genetic abnormalities Environmental factors, or physiological issues. Gametes are unable to successfully fuse during fertilization due to problems such as Genetic mutations, chromosomal abnormalities, or the inability to reach each other in the reproductive tract It can result in the failure to conceive or produce viable offspring.
- 49. Bufo fowleri • Mating and sperm transfer takes place but egg is not fertilized. • In Drosophila vaginal wall swells killing spermatozoa should interspecific crosses take place. • If mating takes place between Bufo fowleri and Bufo valliceps, sperms cannot penetrate the egg membrane of each other, leading to the mortality of gametes. Bufo valliceps
- 54. 2. Postzygotic Barriers: • These barriers occur after the formation of a zygote (fertilized egg). • a. Hybrid Inviability: The zygote is formed but does not develop properly, leading to the death of the hybrid embryo. Example: A horse and a donkey can mate to produce a mule, but mules are often sterile and unable to reproduce. • b. Hybrid Sterility: Hybrids may develop but are sterile, preventing gene flow between species. Example: The hybrid between a lion and a tiger, called a liger, is often sterile. • c. Hybrid Breakdown: The first-generation hybrids may be viable and fertile, but when they mate with each other or with either parent species, the subsequent generations are often weak or infertile. Example: Some cultivated rice varieties show hybrid breakdown when the second-generation hybrids have reduced yield and quality. Reproductive isolation mechanisms play a crucial role in the process of speciation, where new species arise as populations become reproductively isolated from one another and accumulate genetic differences over time
- 56. DOBZHANSKY-MULLER MODEL • The Dobzhansky-Muller model, also known as the Dobzhansky-Muller incompatibilities or speciation genes model, is a theoretical framework in evolutionary biology that helps explain the genetic basis of reproductive isolation between two diverging populations or species. • This model was developed independently by two prominent evolutionary biologists, Theodosius Dobzhansky and Hermann J. Muller, in the mid-20th century.
- 57. • The central idea of the Dobzhansky-Muller model is that when two populations of a common ancestral species diverge and accumulate genetic changes (mutations) independently over time, they may eventually become reproductively isolated from each other. • It means that individuals from these two populations can no longer interbreed or produce viable and fertile offspring • The model proposes that these reproductive barriers arise due to the evolution of genetic incompatibilities between the genes of the two populations. • Specifically, it suggests that when alleles (alternative forms of genes) from one population interact with alleles from the other population, they can produce negative epistatic interactions. • Negative epistasis occurs when the combined effect of two alleles together is deleterious, even if each allele is individually functional or beneficial within its own population
- 58. The key elements of the Dobzhansky-Muller model are: Ancestral Population: Initially, there is a single, interbreeding population. Genetic Divergence: Over time, this population becomes geographically isolated or undergoes genetic changes due to various factors like mutation, natural selection, genetic drift, or geographic isolation. These changes result in the accumulation of different alleles in each population. Incompatibility Alleles: Some of the alleles in each population may be functionally adapted to the genetic background of that population. However, when individuals from these divergent populations come into contact or attempt to mate, certain combinations of alleles may lead to incompatibilities. These incompatibilities can result in reduced fitness or reproductive failure in hybrid offspring.
- 59. Reproductive Isolation: • The genetic incompatibilities between the populations act as a barrier to gene flow. • This can lead to reproductive isolation, where hybrids between the populations have reduced fitness or are inviable, preventing further interbreeding between the populations
- 60. • In the ancestral population, the genotype is AABB. • When two populations become isolated from each other, new mutations can arise. • In one population A evolves into a, and in the other B evolves into b. • When the two populations hybridise it is the first time a and b interact with each other. • When these alleles are incompatible, we speak of Dobzhansky–Muller incompatibilities.
- 61. Significance of isolating mechanism. The isolating mechanism protects the gene pool of a species and prevents hybridization. It prevents the wastage of gametes and energy. A weak isolating mechanism leads to the production of new species through hybridization. The absence of an isolating mechanism leads to the production of new species by instant speciation. Geographical isolation followed by reproductive isolation ultimately leads to the production of new species. Isolating mechanisms protect the identity of a species, which all species fiercely guard