一、一般而言，1到10的数字通常用拼写形式或单词表示，10以上的数字用阿拉伯数字表示。如：
 
1. However, as shown in part B, second-division segregation is indicated by any of four patterns: AaAa, aAaA, AaaA, and aAAa.
 
2. An example is found in the human ABO blood groups, which are determined by three alleles denoted IA, IB and IO.
 
3. There are five distinct classes of antibodies.
 
4. The progeny were 99 resistant to both insecticides, 88 resistant to DDT only, 89 resistant to Dieldrin only, and 106 sensitive to both insecticides.
 
二、通常数字后面有单位，多个数字一起比较，或表示比例、范围、算式时用阿拉伯数字表示。如：
 
1. The genome of E. coli is a circular DNA molecule about 1500 µm long compacted inside a cell only about 2 µm long and 1 µm in diameter.
 
2. The smallest fish is about 4 inches long.
 
3. Any markers separated by more than 2 minutes will not be cotransduced by phage P1.
 
4. Complete replication of all chromosomes in eukaryotes usually takes 5-10 days.
 
5. For P values ranging from 0.01 to 0.05, the probability that chance alone would lead to a fit as bad or worse is between 1 in 20 experiments and between 1 in 100, respectively.
 
6. Spontaneous damage to DNA in human cells takes place at a rate of approximately 1 event per billion nucleotide pairs per minute.
 
7. The aα diploid can undergo meiosis to produce four-spored asci containing haploid a and α spores in the ratio 2 : 2.
 
8. In E. coli, the length is typically 2-5 nucleotides; in eukaryotic cells, it is generally 5-8 nucleotides.
 
9. In mice, the light chains are formed from combinations of about 250 V regions and 4 J regions, giving 250 × 4 = 1000 different possible chains.
 
10. Bacteriophage MS2 has only four genes in a single-stranded RNA molecule containing 3569 nucleotides. SV40 virus has a genetic complement of five genes in a circular double-stranded DNA molecule of about 5 kb.
 
三、句首为数字时用拼写形式而不用阿拉伯数字形式。实际上，英文句子结构灵活，句首少见有超过10的数字。
 
1. Three different alleles of the gene are known.
 
2. Four independent integrations of the F factor into the chromosome of an unusual strain of E. coli yielded four different Hfr derivatives of the strain.
 
3. One hundred people representing the private sector, voluntary organizations, education, federal and state government convened to participate in an invitational national Conservation Learning Summit held November 4-6, 2005 at the National Conservation Training Center in Shepherdstown, West Virginia.
来源：科学网