地理作業

The first step in this process is the development of genetic variability in a population. This genetic variety occurs through mutations:random changes in the structure or number of DNA molecules in a cell (Figure 11 on p. S36 in Supplement 7)that can be inherited by offspring. Most mutations result from random mistakes that sometimes occur in coded genetic instrictions when DNA molecules are copied each time a cell divides and whenever an organism reproduces. Some mutations also occur from exposure to external agents such as radioactivity, X rays, and natural and human-made chemicals(called mutagens).

Mutations can occur in any cell,but only those in reproductive cells are passed on to offspring. Sometimes a mutation can result in a new genetic trait that gives an individual and its offspring better chances for survival and reproduction under existing environmental conditions or when such conditions change.


在這個過程中第一步是基因可變性在人口方面的發展,基因品種通過變化發生:改變細胞中的DNA的結構或數量(在P.S36的補充7圖11)在被編碼的基因中有時發生錯誤的變化結果,當DNA細胞分裂時,有些變化也從對外的媒介像是放射線,X光,人造化學製品中發生.

變化在所有細胞中都有可能發生,但是只有在生殖細胞中的才會傳遞到後代,有時變化可能會出現一種新的基因特徵導致一個個體和他的後代在現有的環境下或是環境改變時有更好的機會生存和生產