玉米的基因型与性别对应关系如下表，已知B、b和T、t分别位于两对同源染色体上。<table style="BORDER-BOTTOM: medium none; BORDER-LEFT: medium none; WIDTH: 89.98%; BORDER-COLLAPSE: collapse; BORDER-TOP: medium none; BORDER-RIGHT: medium none; mso-border-alt: solid black .5pt; mso-yfti-tbllook: 1184; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt; mso-border-insideh: .5pt solid black; mso-border-insidev: .5pt solid black" border="1" cellspacing="0" cellpadding="0" width="89%" _dj="MsoNormalTable"><tbody><tr style="HEIGHT: 38.8pt; mso-yfti-irow: 0; mso-yfti-firstrow: yes"><td style="BORDER-BOTTOM: black 1pt solid; BORDER-LEFT: black 1pt solid; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 11.62%; PADDING-RIGHT: 5.4pt; HEIGHT: 38.8pt; BORDER-TOP: black 1pt solid; BORDER-RIGHT: black 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid black .5pt" width="11%" nowrap="">基因型</td><td style="BORDER-BOTTOM: black 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 29.12%; PADDING-RIGHT: 5.4pt; HEIGHT: 38.8pt; BORDER-TOP: black 1pt solid; BORDER-RIGHT: black 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid black .5pt; mso-border-left-alt: solid black .5pt" width="29%" nowrap="">B和T同时存在（<u>B    T    </u>）</td><td style="BORDER-BOTTOM: black 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 32.1%; PADDING-RIGHT: 5.4pt; HEIGHT: 38.8pt; BORDER-TOP: black 1pt solid; BORDER-RIGHT: black 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid black .5pt; mso-border-left-alt: solid black .5pt" width="32%" nowrap="">T存在，B不存在（<u>bbT   </u>）</td><td style="BORDER-BOTTOM: black 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 27.16%; PADDING-RIGHT: 5.4pt; HEIGHT: 38.8pt; BORDER-TOP: black 1pt solid; BORDER-RIGHT: black 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid black .5pt; mso-border-left-alt: solid black .5pt" width="27%" nowrap="">T不存在（<u>B   tt或bbtt</u>）</td></tr><tr style="HEIGHT: 22.4pt; mso-yfti-irow: 1; mso-yfti-lastrow: yes"><td style="BORDER-BOTTOM: black 1pt solid; BORDER-LEFT: black 1pt solid; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 11.62%; PADDING-RIGHT: 5.4pt; HEIGHT: 22.4pt; BORDER-TOP: #000000; BORDER-RIGHT: black 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid black .5pt; mso-border-top-alt: solid black .5pt" width="11%" nowrap="">性别</td><td style="BORDER-BOTTOM: black 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 29.12%; PADDING-RIGHT: 5.4pt; HEIGHT: 22.4pt; BORDER-TOP: #000000; BORDER-RIGHT: black 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid black .5pt; mso-border-left-alt: solid black .5pt; mso-border-top-alt: solid black .5pt" width="29%" nowrap="">雌雄同株异花</td><td style="BORDER-BOTTOM: black 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 32.1%; PADDING-RIGHT: 5.4pt; HEIGHT: 22.4pt; BORDER-TOP: #000000; BORDER-RIGHT: black 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid black .5pt; mso-border-left-alt: solid black .5pt; mso-border-top-alt: solid black .5pt" width="32%" nowrap="">雄株</td><td style="BORDER-BOTTOM: black 1pt solid; BORDER-LEFT: #000000; PADDING-BOTTOM: 0cm; BACKGROUND-COLOR: transparent; PADDING-LEFT: 5.4pt; WIDTH: 27.16%; PADDING-RIGHT: 5.4pt; HEIGHT: 22.4pt; BORDER-TOP: #000000; BORDER-RIGHT: black 1pt solid; PADDING-TOP: 0cm; mso-border-alt: solid black .5pt; mso-border-left-alt: solid black .5pt; mso-border-top-alt: solid black .5pt" width="27%" nowrap="">雌株</td></tr></tbody></table>若BbTt的玉米植株做亲本，自交得F₁代，让F₁中的雌雄同株异花植株相互交配，则F₂代中雌、雄株的比例是