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异源多倍体（种间杂交 — 杂种染色体加倍）：

异源多倍体（种间杂交 — 杂种染色体加倍）：

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异源多倍体（种间杂交 — 杂种染色体加倍）：

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  1. 异源多倍体（种间杂交—杂种染色体加倍）： Allopolyploids：allopolyploid are formed from hybrids between closely related species. The different sets of chromosomes are sufficiently different in DNA sequence not to pair between sets in meiosis. The chromosome number doubles accidentally by failed mitosis so that each cell has two complete sets of chromosomes from each parent , and these pair like with like, restoring fertility.

  2. e.g. 萝卜甘蓝 萝卜 (2x=18) × 甘蓝 (2x=18) F1 杂种 (2n=2x=18=9+9) 9条来自萝卜—R; 9条来自甘蓝—B. F1 - RB 无对应同源染色体，减Ⅰ不配对，形成18个单价体，随机分离不均衡，配子几乎全部不育 偶尔可育(18个单价体在一个配子中） 自交 F2 株型大，根像萝卜，叶像甘蓝，且可育 2n=4x=36=(9+9)x2 F2 (RRBB) (36) 可育配子（18=9R+9B）

  3. 异源六倍体小麦的形成： AA x BB (2n=2x=14) (2n=2x=14) AB 不育配子，加倍 AABB x DD （2n=4x=28) (2n=2x=14) ABD (2n=3x=21) 不育配子，加倍 AABBDD （2n=6x=42) 可育异源六倍体小麦

  4. e.g. 小黑麦（异源八倍体） 普通六倍体小麦 AABBDD × RR二倍体黑麦 6x=42 2x=14 配子 ABD R F1 ABDR 28（21+7） 染色体加倍 AABBDDRR (8x=56)

  5. 多倍体的诱发： 物理 化学 0.01%~1.0%的秋水仙素诱导 e.g. 无籽西瓜(同源三倍体)： 西瓜苗期（2x=22）秋水仙素处理 （4x=44） 　　　　　母本 4x × 2x 父本 F1 3x=33 二倍体花粉刺激 无籽果实发育

  6. 6.2.2 Aneuploidy非整倍体 Aneuploidy refers to small deviations from the chromosome numbers of the series. 染色体非整倍数改变：核内染色体数通常以二倍体(2x)染色体数作为标准，在此基础上增减个别几条染色体 非整倍体 Monosome(单体) 2x-1 (ABCD)(ABC) 缺一条 Trisomy(三体) 2x+1 (ABCD)(ABCD)(A) 多一条 Tetrasomy(四体) 2x+2 (ABCD)(ABCD)(AA) 多相同2条 Ditrisomy(双三体) 2x+1+1 (ABCD)(ABCD)(AB) 各多一条 Nullisomic(缺体) 2x-2 (ABC)(ABC) 缺相同两条

  7. Aneuploid aberrance：infertile * 大多数动植物单体都不能存活 黑腹果蝇 (2x=8) X，Y染色体 （I ）: 多/少1条 影响生育 V形染色体（II、III）: 多/少1条 致死 点状染色体 （IV）: 多（三体 2x+1=9）/少1条（单体 2x-1=7） 可以存活、繁殖

  8. 人 (2n=46) 常染色体三体 (2n+1=47) 胚胎期致死—自发性流产 21三体先天愚型（Down’s syndrome – 唐氏综合症，1/750） 常染色体单体 (2n-1=45) 致死 性染色体 单体 XO （Turner’s syndrome - 特纳氏综合症， 1/10000） YO不能存活 三体 XXX（1/2000）、 XXY（1/2000） 四体 XXXX、XXYY 可存活但表型异常

  9. Aneuploidgametes arise from errors at both first and second division of meiosis through a process known as nondisjunction. This is where either two homologous chromosomes fail to separate at meiosis I or a centromere fails to split at metaphase of meiosis II.

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