Объяснение:
When you look at two organisms, it is hard to decide by comparing only their
physical characteristics if they are in the same species or not. Two organisms can
look similar but be in different species. For example, cheetah, leopard and jaguar
look similar, but they are three different species. On the other hand, dogs look
different, but they are one species.
For new species to be produced, organisms must undergo reproductive isolation.
It means, they should not be able to interbreed and produce offspring. The
process of formation of new species is called speciation. There are two main
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types of speciation: allopatric and sympatric.
Allopatric speciation
Two organism can be reproductively isolated by geographical barriers. For
example, one part of bird population moves from the mainland to an island. It is
separated from the original population. Here, on the island plants and animals
are different from the mainland. These birds start to adapt to new environment
and change their characteristics. Birds interbreed and over time new generations
become different from the original population on the mainland. These two
populations now cannot interbreed. A new species is formed.
There can be different geographical barriers, for example, large forest can
become split, if part of the trees are cut. So, organisms become isolated from
each other. Speciation when populations are isolated geographically is called
allopatric speciation.
Sympatric speciation
Sympatric speciation is the speciation when there is no geographical barriers.
Organisms are located in one area, but become reproductively isolated.
Polyploidy is the example of sympatric speciation.
Polyploid organism is an organism with more than two sets of chromosomes (3n,
4n, 5n, etc.). It can happen if chromosomes do not separate during gamete
formation. This gametes will be diploid (2n). Then, when these gametes fuse, the
resulting zygote will be tetraploid (4n).
This tetraploid organism can not reproduce sexually, because it is hard to
undergo meiosis and produce gametes. But this organism can easily reproduce
asexually and produce offspring. This offspring can grow and produce a
population of tetraploid organisms. So, the resulting population cannot
interbreed with the original diploid population. They are considered a new
species. Polyploidy mostly happens in plants.
Відповідь:
Тихо, поволі ,нога за ногою, пливе валка битим шляхом у безлюдній пустелі. На горизонті, між жовтим житом та синім небом, зеленіли тополі. (М. Коцюбинський) Ви на горі, на самому вершечку. (Панас Мирний) В одному з мальовничих місць Ялти, біля самого моря, височать корпуси будинку відпочинку. (О. Донченко) А полум’я йшло далі, в осередок току до клуні. Микола з товаришами помандрував на сахарні в Канівщину, в Стеблів. (І. Нечуй-Левицький)
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