1 . 某校高三年级有
个班,每个班均有
人,第
(
)个班中有
个女生,余下的为男生.在这n个班中任取一个班,再从该班中依次取出三人,若第三次取出的人恰为男生的概率是
,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0f3cb8d72bb2e281b943b3b430138ef7.png)
_________ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/aa93831adff23d37f3eee7f297d3c1a7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/14da4272a5d4b7b0ffe7322e7693bf13.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f0a532e15e232cb4b99a8d4d07c89575.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/eece89a108c1ec44e1a2d8ee78fd9732.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/11fee724808afa73331e54226af13a75.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/355390efe2ad5920e12e022306149ddf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0f3cb8d72bb2e281b943b3b430138ef7.png)
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解题方法
2 . 在孟德尔遗传理论中,称遗传性状依赖的特定携带者为遗传因子,遗传因子总是成对出现,例如,豌豆携带这样一对遗传因子:
使之开红花,
使之开白花,两个因子的相互组合可以构成三种不同的遗传性状:
为开红花,
和
一样不加区分为开粉色花,
为开白色花,生物在繁衍后代的过程中,后代的每一对遗传因子都包含一个父本的遗传因子和一个母本的遗传因子,而因为生殖细胞是由分裂过程产生的,每一个上一代的遗传因子以
的概率传给下一代,而且各代的遗传过程都是相互独立的,可以把第
代的遗传设想为第
次试验的结果,每一次试验就如同抛一枚均匀的硬币,比如对具有性状
的父本来说,如果抛出正面就选择因子
,如果抛出反面就选择因子
,概率都是
,对母本也一样,父本、母本各自随机选择得到的遗传因子再配对形成子代的遗传性状,假设三种遗传性状
,
(或
),
在父本和母本中以同样的比例
出现,则在随机杂交试验中,遗传因子
被选中的概率是
,遗传因子
被选中的概率是
,称
、
分别为父本和母本中遗传因子
和
的频率,
实际上是父本和母本中两个遗传因子的个数之比,基于以上常识回答以下问题:
(1)如果植物的上代父本、母本的遗传性状都是
,后代遗传性状为
,
(或
),
的概率分别是多少?
(2)对某一植物,经过实验观察发现遗传性状
具有重大缺陷,可人工剔除,从而使得父本和母本中仅有遗传性状为
,
(或
)的个体,在进行第一代杂交实验时,假设遗传因子
被选中的概率为
,
被选中的概率为
,其中
、
为定值且
,求杂交所得子代的三种遗传性状
,
(或
),
所占的比例
,
,
;
(3)继续对(2)中的植物进行杂交实验,每次杂交前都需要剔除
的个体.假设得到的第
代总体中3种遗传性状
,
(或
),
所占的比例分别为:
,
,
,设第
代遗传因子
和
的频率分别为
和
,已知有以下公式
,
,![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2095339efed26ceec932ad2f9ef9e21c.png)
(ⅰ)证明
是等差数列;
(ⅱ)求
,
,
的通项公式,如果这种剔除某种遗传性状的随机杂交实验长期进行下去,会有什么现象发生?
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/306ac9722099868f11c37067a24f3892.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8e25893a9dc7878e82704f1eca13cd6a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/69fa77d305db1c083465d3895d45dc53.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d5604a87a7559957790a4256fdb9ae1e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f89eef3148f2d4d09379767b4af69132.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8f72c3b3c76c6425af1dc19e294aef9d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6c4929d6cf167d87aca3066dfe9e922a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b1010846eeec6c9da29640f5aa3f8738.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9aa8a716a31b0f51b70fdf9bdb257909.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5b75fc182d81803f162afef21ca1ccd4.png)
(1)如果植物的上代父本、母本的遗传性状都是
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8e25893a9dc7878e82704f1eca13cd6a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/306ac9722099868f11c37067a24f3892.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8e25893a9dc7878e82704f1eca13cd6a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/69fa77d305db1c083465d3895d45dc53.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d5604a87a7559957790a4256fdb9ae1e.png)
(2)对某一植物,经过实验观察发现遗传性状
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d5604a87a7559957790a4256fdb9ae1e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/306ac9722099868f11c37067a24f3892.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8e25893a9dc7878e82704f1eca13cd6a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/69fa77d305db1c083465d3895d45dc53.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b1010846eeec6c9da29640f5aa3f8738.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9aa8a716a31b0f51b70fdf9bdb257909.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b1010846eeec6c9da29640f5aa3f8738.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9aa8a716a31b0f51b70fdf9bdb257909.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8b70d4a3fc3e01b5a6358cf4e57578e6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/306ac9722099868f11c37067a24f3892.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8e25893a9dc7878e82704f1eca13cd6a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/69fa77d305db1c083465d3895d45dc53.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d5604a87a7559957790a4256fdb9ae1e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/caa55bc54cd6c2dc5ff0f125ac1a2ff5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f44c235d8b49207ad3f2d77dc5d6cf20.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3c3871a062c5e0a4e009b01aa47afb48.png)
(3)继续对(2)中的植物进行杂交实验,每次杂交前都需要剔除
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d5604a87a7559957790a4256fdb9ae1e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/306ac9722099868f11c37067a24f3892.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8e25893a9dc7878e82704f1eca13cd6a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/69fa77d305db1c083465d3895d45dc53.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d5604a87a7559957790a4256fdb9ae1e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4cff9404d1a61595ff7681ec385b8d2a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/aa08e0ffe553c48c67d37cda26b46a4a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7b19ea7c42030ea26e1b702932e614aa.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6a24198bd04c29321ae5dc5a28fe421.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3ffb021aa7d5a5c2f0691e337caad624.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0ce603aa3abcb61750d2191aaa13dddc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d0bcd21db3c870bff7037735313648c6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7fe1b3406b91579c3d4576fd309bdf3e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2095339efed26ceec932ad2f9ef9e21c.png)
(ⅰ)证明
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a28a32aa53105ca3944205fbf56ec5ea.png)
(ⅱ)求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9bd4033c8a46a2a5645a7b5016308a21.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d15dab5ad72b1d9b9b918bf40ae3bf4f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d49064344f88c55bb70e4b5ebaa33855.png)
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