Microspore abortion occurred after the tetrad formation.是什么意思？

Microspore abortion occurred after the tetrad formation.

小孢子败育发生在四分体形成以后.

microspore

n. 小孢子，（种子植物的）花粉粒；

例句
The microspore culture technology has been widely applied in Brassica species nowadays.
随着芸苔属作物小孢子培养技术的日趋成熟,应用范围也越来越广泛.

abortion

n. 流产，流产的胎儿，畸形，夭折；

例句
There are many people who still find the act of abortion abhorrent.
仍有很多人对堕胎行为表示厌恶。

occurred

v. 发生(occur 的过去分词)；

例句
The deaths occurred when police acted to stop widespread looting and vandalism...
警方采取行动制止猖狂的打砸抢行为时有多人丧生。

after

prep. …后的，（表示时间）在…以后，（表示位置、顺序）在…后面；conj. 在…以后；adv. 以后，继后；adj. 后来的，以后的；

例句
Her lover walked out on her after she had aborted their child.
她的情人在她打掉胎儿后甩了她。

the

art. 指已提到的人（物），指说话人与听者已知的人（物），用于独一无二的事物前，与形容词最高级和序数词连用；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

tetrad

n. 四元组，四分染色体，<化>四价元素，（数目）4；

例句
Cytokinesis was simultaneous and the arrangement of microspores in the tetrad was tetrahedral.
胞质分裂为同时型,四分体中小孢子排列呈正四面体形.

formation

n. 形成，构成，结构，形成物，编队，队形；

例句
The Prime Minister resigned today, clearing the way for the formation of a new government...
首相今天的辞职为新政府的组建扫清了道路。