科普專欄–薯不揀單 - 深入淺出–牛究竟天生有沒有角？

動物的品種不同，其特徵亦會有所不同。以狗為例的話，金毛尋羊犬以及臘腸狗就是非常鮮明的例證。519Please respect copyright.ＰＥＮＡＮＡj0L8oBU16c
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至於牛隻，農場飼養用的大致分為兩種，主力出產牛奶的乳牛(Dairy Cattle)和主力屠宰成肉類出售的肉用牛(Beef Cattle)。519Please respect copyright.ＰＥＮＡＮＡZ4S8zD9D5L
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各舉一例的話，前者品種例子為Holstein(荷斯坦)，而後者則為較為廣泛認識的Angus(安格斯)。519Please respect copyright.ＰＥＮＡＮＡna3cQzVxH1
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牛天生會否長角，將視乎品種而定。大多數的乳牛品種天生均長有角，而食用牛多數的品種則天生無角。519Please respect copyright.ＰＥＮＡＮＡr5zhkUkyaH
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這裡讓農夫感到煩惱的是，乳牛隻會利用頭上的角互相攻擊對方甚至自己。519Please respect copyright.ＰＥＮＡＮＡ4JdzACGO1Q
因此慣常的做法會麻醉牛隻然後再進行除角手術，以免牛隻受傷因而損失獲利，但這做法引起動物權益成員的關注及爭議，認為此舉會對牛隻帶來創傷。519Please respect copyright.ＰＥＮＡＮＡcXlWa3uOVD
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（圖2）最為有效率及一勞永逸的解決辦法，自當然就是培育沒有長角的品種，一直傳遞下去。519Please respect copyright.ＰＥＮＡＮＡnCgcKsq6lL
有科學家致力尋求發現，發現牛隻基因染色體1的某一段位置的重覆區域，將會導致乳牛品種不會長出牛角。519Please respect copyright.ＰＥＮＡＮＡqvpyRHBJfZ
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（圖3）因此，他們嘗試抽取長角品種的皮膚細胞，利用CRISPR基因編輯技術在那段基因區域上加添重覆區域（Ref1)，再經過一系列的工序，將已編輯的細胞人工培植到牛隻身上，觀察誕下的胎兒會否長出牛角。519Please respect copyright.ＰＥＮＡＮＡPGrB2tRCvv
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（圖4）最終所誕下的牛隻的而且確沒有長角，但因器官衰竭等問題很快便與世長辭。519Please respect copyright.ＰＥＮＡＮＡZvaDb7XJYs
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這研究確實了CRISPR技術在牛隻的應用，但顯然仍有一系列的應用問題需要改善。在這實驗中，6隻人工培植受孕的牛隻中，只有一隻成功誕下嬰兒。519Please respect copyright.ＰＥＮＡＮＡfTRDZqdjsB
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至於為何不重點培育沒有長角品種的乳牛，原因是牠的產奶量較其他有角品種的最少。519Please respect copyright.ＰＥＮＡＮＡwv9UFwJZGw
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農父及科學家的最終目標，當然就是希望培植沒有長角而產奶量豐盛的牛隻。但這做法是否符合動物權益，這又會是一場永無休止的辯論。519Please respect copyright.ＰＥＮＡＮＡFYWaSUgoiY
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Ref1:https://www.nature.com/articles/s41598-020-70531-y519Please respect copyright.ＰＥＮＡＮＡOgaRyr7cL4