Первый слайд презентации
Crimean state medical University named after S. I. Georgievsky Submitted by Ajay Sharma Submitted to Anna Zukhova Georgievsky
01 What is Speciation ? Contents 02 What is Reproductive Isolation ? Contents 03 Isolation mechanism & types :- Prezygotic isolation mechanism Postzygotic isolation mechanism Contents 04 Example Contents
A population or group of populations whose members have the ability to interbreed with one another under natural condition and produce fertile offspring and reproductively isolated from other species. In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction.
The diversity of species on Earth is simply astounding. Scientists have identified about two million species and still do not know how many species inhabit Earth. Scientists estimate as many as 30 million species may inhabit Earth. So, the big question is how did so many species form?
Speciation Speciation = formation of new species Speciation occurs when members of similar populations no longer interbreed to produce fertile offspring within their natural environment It occurs when groups in a species become reproductively isolated and diverge A single species can generate multiple species HENCE IT LEAD TO A NEW IDEAS ABOUT EVOLUTION Speciation is the origin of new species. Speciation increases our planet’s biological diversity. Therefore, speciation is an important part of the theory of evolution. Many scientist have different ideas about it.
Reproductive Isolation The existence of biological factors (barriers) that prevent two individuals of a species from mating and producing viable and fertile offspring A new species will form when reproductive isolation occurs The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviours and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offspring are sterile. These barriers maintain the integrity of a species by reducing gene flow between related species
Geographical isolation occurs when populations cannot mate because of physical barriers Geographically separated populations aren’t necessarily distinct species. Example: Northern Spotted Owl and Mexican Spotted Owl. Geographical Isolation
Isolation mechanism Isolating mechanisms prevent interbreeding and maintain reproductive isolation. Isolating mechanisms can be divide in to two different types. Isolating mechanisms that occur before fertilization are called Prezygotic isolating mechanisms. Isolating mechanisms that occur after fertilization are called postzygotic isolating mechanisms.
PRE-ZYGOTAIC BARRIER Pre-zygotic barriers are obstacles that are present before an egg can be fertilized. A zygote is an egg that has been fertilized by a sperm Premating isolating mechanisms include: 1) Ecological isolation. 2) Temporal isolation. 3) Behavioral isolation. 4) Mechanical incompatibility. 5) Gametic isolation
Ecological isolation Ecological isolation occurs when potential mates never meet because they live in different habitats. Ex. The mountain bluebird lives at high elevation while the eastern bluebird prefers low elevation
Temporal isolation Temporal isolation occurs when species can’t mate because they breed at different times of year. Ex: The Monterey Pine and the Bishop pine have different pollination periods. Example Red and black sea urchins live in the same location, but release their gametes at different times of the year.
Mechanical incompatibility Mechanical incompatibility occurs when species cannot mate because their reproductive structures are incompatible Closely related species may attempt to mate but fail because they are anatomically incompatible and transfer of sperm is not possible In animals with internal fertilization, male and female sexual organs may not fit together EX. snails of species whose shells have left handed spirals may be unable to successfully copulate with snails whose shells have right handed spirals
GAMETIC ISOLATION Sperm of one species may not survive internal environment of female reproductive tract in another species For fertilization to occur, the sperm must reach the ovum. For this to happen they usually attract each other through chemical means, but the chemicals might vary from one specie to another. In this case gametes won’t recognise each other and fertilization won’t take place.
Behavioral isolation Behavioral isolation occurs when species can’t mate because patterns of courtship may be different to the extent that sexual union is not achieved Ex: Fireflies produce patterns of flashes that attract their mates. Over 2000 species of fireflies are isolated based on the patterns of flashes Members of the two species will not mate with each other because they use different songs to attract mates. Eastern meadowlarks will not respond to western meadowlark songs, and vice versa. Example: Eastern and Western Meadowlarks
POSTMATING ISOLATING MECHANISM Isolating mechanisms which operate after fertilization Prevents hybrid zygotes from developing into viable, fertile adults There are three likely cases that will occur to ensure that the hybrid does not reproduce Postmating isolating mechanisms include: 1. Hybrid inviability 2. Hybrid infertility 3. Hybrid breakdown
HYBRID INVIABILITY The term 'hybrid' refers to the offspring between two different species and 'inviability' refers to an organism that does not thrive. In hybrid inviability, mating occurs and a hybrid is produced, but Hybrid very weak and can’t live outside the uterus. Ex. Several species of the frog live in the same habitats but hybrids do not complete development If Sheep and goats mate then Hybrid zygotes Die before birth The creation of an unsuccessful hybrid is also a form of post- zygotic barrier.
ABNORMALITIES Species mate and hybrid is viable but sterile. If chromosome numbers are different, meiosis cannot produce normal gametes EX. Male donkey x Female horse Mule Mules: Healthy (viable)
Conclusion- (1)The reproductive isolation is quite difficult in human because of the invention of different medium of transport. (2)It can be seen in animals but it is rare in human as human beings can travel to any place to reproduce.(3)WHO says no to gene edited babies.