12/31/2023 0 Comments Platypus lay eggs or not![]() Evolutionary biologist and research leader Guojie Zhang explains this new research: “holds the key as to why we and other eutherian mammals evolved to become animals that give birth to live young instead of egg-laying animals.” The monotreme’s egg-laying ability may have been something other mammals lost as they evolved compared to an ability that monotremes gained after mammals diverged. This broken-down sex determination system may be more comparable to the ZW sex determination of an egg-laying bird rather than a mammal’s XY system. This suggests that these chromosomes may have been arranged in a ring shape and as mammals have evolved it has slowly broken down into smaller pieces of X and Y chromosomes. The platypus however has 10 sex chromosomes. Eutherian and marsupials have an XY system, meaning that the sex of an offspring is determined by two chromosomes, one chromosome received from each parent. Another surprising difference between monotremes and the other two types of mammals is their sex determining system. However, platypuses and echidnas have one copy, providing a good reason as to why these mammals lay eggs compared to giving birth to live young. Unsurprisingly this type of gene is not usually found in mammals such as humans. ![]() Most birds have the vitellogenin gene, this gene encodes egg yolk proteins which provide nutrients to developing embryos. The new genome helps explain the peculiar overlap of the platypus with bird and reptile characteristics. This suggests that these chromosomes may have been arranged in a ring shape It suggests monotremes diverged from the other two mammal types 187 million years ago. The new research offers insight answering questions about when these three types of mammals diverged from each other. Koalas, for example, belong to marsupials because they have permanent pouches. Humans belong to the eutherian subclass which give birth to live young. This type of mammal both lays eggs and feeds its young with milk. The platypus species is one of only five examples of monotremes left on earth including the echidna species (also known as spiny anteaters) which has also been sequenced in this research. Mammals are split into three different types: monotremes, eutherians, and marsupials. Up until now only 25% of the genome had been mapped in a 2008 study. This newest platypus genome sequencing attempt has contextualised 96% of the platypus’ genome. The platypus species is one of only five examples of monotremes left on earth ![]() This research gives new insight into the evolutionary mechanisms involved in creating one interesting creature. Over 200 years later the near complete genome of the Platypus has been mapped by researchers and published in Nature. It shocked zoologist George Shaw when he came across the mammal in 1799. The platypus feeds its young with milk like a mammal, lays eggs like a bird, and produces venom like a reptile.
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