为了解基因结构，通常选取一特定长度的线性DNA分子，先用一种限制酶切割，通过电泳技术将单酶水解片段分离，计算相对大小；然后再用另一种酶对单酶水解片段进行降解，分析片断大小。下表是某小组进行的相关实验。<table style="BORDER-BOTTOM: medium none; BORDER-LEFT: medium none; BORDER-COLLAPSE: collapse; BORDER-TOP: medium none; BORDER-RIGHT: medium none; mso-border-alt: solid windowtext .5pt; mso-yfti-tbllook: 480; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt; mso-border-insideh: .5pt solid windowtext; mso-border-insidev: .5pt solid windowtext; mso-table-layout-alt: fixed" border="1" cellspacing="0" cellpadding="0" _dj="MsoNormalTable"><tbody><tr style="PAGE-BREAK-INSIDE: avoid; mso-yfti-irow: 0; mso-yfti-firstrow: yes"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: windowtext 1.5pt solid; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 41.4pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; BORDER-RIGHT: windowtext 1.5pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext 1.5pt; mso-border-bottom-alt: solid windowtext .5pt" rowspan="8" width="55">已知一线性DNA序列共有5000bp（bp为碱基对）</td><td style="BORDER-BOTTOM: windowtext 1.5pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 72pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext 1.5pt; mso-border-left-alt: solid windowtext 1.5pt; mso-border-right-alt: solid windowtext .5pt" width="96">第一步水解</td><td style="BORDER-BOTTOM: windowtext 1.5pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 59.6pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-left-alt: .5pt; mso-border-top-alt: 1.5pt; mso-border-bottom-alt: 1.5pt; mso-border-right-alt: .5pt; mso-border-color-alt: windowtext; mso-border-style-alt: solid" width="79">产物（单位bp）</td><td style="BORDER-BOTTOM: windowtext 1.5pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 132.3pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-left-alt: .5pt; mso-border-top-alt: 1.5pt; mso-border-bottom-alt: 1.5pt; mso-border-right-alt: .5pt; mso-border-color-alt: windowtext; mso-border-style-alt: solid" width="176">第二步水解</td><td style="BORDER-BOTTOM: windowtext 1.5pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 87.1pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 1.5pt solid; BORDER-RIGHT: windowtext 1.5pt solid; PADDING-TOP: 0cm; mso-border-left-alt: solid windowtext .5pt" width="116">产物（单位bp）</td></tr><tr style="PAGE-BREAK-INSIDE: avoid; mso-yfti-irow: 1"><td style="BORDER-BOTTOM: windowtext 1.5pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 72pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext 1.5pt; mso-border-left-alt: solid windowtext 1.5pt; mso-border-top-alt: solid windowtext 1.5pt; mso-border-right-alt: solid windowtext .5pt" rowspan="4" width="96">A酶切割　</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 59.6pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext 1.5pt" width="79">2100</td><td style="BORDER-BOTTOM: windowtext 1.5pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 132.3pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-left-alt: .5pt; mso-border-top-alt: 1.5pt; mso-border-bottom-alt: 1.5pt; mso-border-right-alt: .5pt; mso-border-color-alt: windowtext; mso-border-style-alt: solid" rowspan="4" width="176">将第一步水解产物分离后，分别用B酶切割</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 87.1pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1.5pt solid; PADDING-TOP: 0cm; mso-border-left-alt: .5pt; mso-border-top-alt: 1.5pt; mso-border-bottom-alt: .5pt; mso-border-right-alt: 1.5pt; mso-border-color-alt: windowtext; mso-border-style-alt: solid" width="116">1900   200</td></tr><tr style="PAGE-BREAK-INSIDE: avoid; mso-yfti-irow: 2"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 59.6pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="79">1400</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 87.1pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1.5pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; mso-border-right-alt: solid windowtext 1.5pt" width="116"> 800    600</td></tr><tr style="PAGE-BREAK-INSIDE: avoid; mso-yfti-irow: 3"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 59.6pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="79">1000</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 87.1pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1.5pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; mso-border-right-alt: solid windowtext 1.5pt" width="116">1000</td></tr><tr style="PAGE-BREAK-INSIDE: avoid; mso-yfti-irow: 4"><td style="BORDER-BOTTOM: windowtext 1.5pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 59.6pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; mso-border-bottom-alt: solid windowtext 1.5pt" width="79">500</td><td style="BORDER-BOTTOM: windowtext 1.5pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 87.1pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1.5pt solid; PADDING-TOP: 0cm; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="116">500</td></tr><tr style="PAGE-BREAK-INSIDE: avoid; mso-yfti-irow: 5"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 72pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-left-alt: 1.5pt; mso-border-top-alt: 1.5pt; mso-border-bottom-alt: .5pt; mso-border-right-alt: .5pt; mso-border-color-alt: windowtext; mso-border-style-alt: solid" rowspan="3" width="96">B酶切割　</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 59.6pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext 1.5pt" width="79">2500</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 132.3pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext 1.5pt" rowspan="3" width="176">将第一步水解产物分离后，分别用A酶切割</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 87.1pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1.5pt solid; PADDING-TOP: 0cm; mso-border-left-alt: .5pt; mso-border-top-alt: 1.5pt; mso-border-bottom-alt: .5pt; mso-border-right-alt: 1.5pt; mso-border-color-alt: windowtext; mso-border-style-alt: solid" width="116">1900   600</td></tr><tr style="PAGE-BREAK-INSIDE: avoid; HEIGHT: 16.5pt; mso-yfti-irow: 6"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 59.6pt; PADDING-RIGHT: 5.4pt; HEIGHT: 16.5pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="79">1300</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 87.1pt; PADDING-RIGHT: 5.4pt; HEIGHT: 16.5pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1.5pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; mso-border-right-alt: solid windowtext 1.5pt" width="116">800               500</td></tr><tr style="PAGE-BREAK-INSIDE: avoid; HEIGHT: 15pt; mso-yfti-irow: 7"><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 59.6pt; PADDING-RIGHT: 5.4pt; HEIGHT: 15pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt" width="79">1200</td><td style="BORDER-BOTTOM: windowtext 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 87.1pt; PADDING-RIGHT: 5.4pt; HEIGHT: 15pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1.5pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; mso-border-right-alt: solid windowtext 1.5pt" width="116">1000   200</td></tr><tr style="PAGE-BREAK-INSIDE: avoid; mso-yfti-irow: 8; mso-yfti-lastrow: yes; mso-row-margin-right: 87.1pt"><td style="BORDER-BOTTOM: windowtext 1.5pt solid; BORDER-LEFT: windowtext 1.5pt solid; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 41.4pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1.5pt solid; PADDING-TOP: 0cm; mso-border-top-alt: solid windowtext .5pt" valign="top" width="55"> </td><td style="BORDER-BOTTOM: windowtext 1.5pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 72pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid windowtext 1.5pt; mso-border-left-alt: solid windowtext 1.5pt; mso-border-top-alt: solid windowtext 1.5pt; mso-border-right-alt: solid windowtext .5pt" width="96">经A酶和B酶同时切割</td><td style="BORDER-BOTTOM: windowtext 1.5pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 191.9pt; PADDING-RIGHT: 5.4pt; BORDER-TOP: #000000; BORDER-RIGHT: windowtext 1.5pt solid; PADDING-TOP: 0cm; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext 1.5pt" width="256" colspan="2">1900    1000    800    600    500 200</td><td style="BORDER-BOTTOM: #000000; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 0cm; PADDING-RIGHT: 0cm; BORDER-TOP: #000000; BORDER-RIGHT: #000000; PADDING-TOP: 0cm; mso-cell-special: placeholder" width="116"> </td></tr></tbody></table>由实验可知，在这段已知序列上，A酶与B酶的识别序列分别为几个？