Sequencing the strangest animals on earth

image: Lukas / stock.adobe.com
In the late 18th century, Europeans discovered the platypus in Australia, which looks like a beaver and is often considered the strangest mammal in the world. Platypus exhibits a strange set of characteristics: spawning rather than fetal birth, secreting milk, no teeth, toxic stings, and having 10 sex chromosomes. This strange semi-aquatic animal has been bothering researchers.
recently, an international team led by Zhang Guojie, a researcher at
Kunming Animal Research Institute, conducted a unique study of the platypus genome, mapped the complete platypus genome for the first time, and found some answers to the strange features of the platypus. The findings are published in Nature.
" complete genome answers some of the strange features of platypus. Zhang Guojie said decoding the platypus genome is important for a better understanding of how other mammals, including humans, have evolved, which is key to the evolution of real animal mammals into capable spawning rather than spawning animals.
platypus belongs to an ancient mammal, the mono-porous animal, which existed for millions of years before modern mammals appeared. "The platypus belongs to mammals, but genetically it is a mixture of mammals, birds and reptiles. " Zhang Guojie pointed out that the platypus preserved many of the original features of its ancestors, which may help it successfully adapt to the living environment.
one of the most unusual features of platypus is that although it lays eggs, it also has breasts used to feed its young, but the platypus secretes milk not through nipples, but through the pores on both sides of the abdomen.
humans lost three so-called ovoprotein genes during evolution, each of which is important for the production of egg yolks. The study showed that platypus still carried one of the three ovoprotein genes, although two others were lost about 130 million years ago. Platypus continues to lay eggs with this remaining gene, possibly because platypus provides milk for its cubs, rather than relying on the production of ovoproteins as birds and reptiles do.
in all other mammals, the ovoprotein gene has been replaced by the casein gene, which produces casein, the main ingredient in mammalian milk. The study showed that platypus also carries casein genes, so its milk content is very similar to that of cows, humans and other mammals.
"This tells us that the milk production capacity of all existing mammals was developed through the same set of genes that came from a common ancestor that was 170 million years old, similar to the early Jurassic dinosaurs," Zhang said. Another
the platypus is that it has no teeth, and modern platypus has two horn plates for mashing food. The study showed that the platypus' teeth fell out about 120 million years ago, when four of the eight genes responsible for tooth development disappeared.
researchers also looked at how platypuses determine gender. Humans and all other mammals on Earth have two sex-determining sex chromosomes: the X and Y chromosome systems, where XX is female and XY is male. However, platypus has 10 sex chromosomes, 5 X and 5 Y chromosomes.
thanks to a near-complete chromosomal-level genome, the researchers suggest that the 10 sex chromosomes of the platypus are arranged in a ring and then broken down into small fragments of the X and Y chromosomes. At the same time, genome maps show that most mono-porous animals have more sex chromosomes in common with chickens than with humans, indicating an evolutionary link between mammals and birds. (Source: Xin Yu, China Science Journal)
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