评论
打印
Have you ever wondered why you are different from your siblings?
你有没有想过为什么你和你的兄弟姐妹不一样？
The answer lies within the amazing process of meiosis.
答案就在惊人的减数分裂过程中。
What is Meiosis?
什么是减数分裂？
Meiosis is a process where a single cell divides twice to produce four cells containing half the original amount of genetic information.
减数分裂是一个分裂过程，单个细胞分裂两次，产生四个细胞，其中包含一半的原始遗传信息。
These cells are our sex cells – sperm in males, eggs in females.
这些细胞是我们的性细胞——男性的精子，女性的卵细胞。
During meiosis, one cell divides twice to form four daughter cells.
在减数分裂过程中，一个细胞分裂两次，形成四个子细胞。
These four daughter cells only have half the number of chromosomes than the parent cell; they are haploid.
这四个子细胞的染色体数目只有母细胞的一半；它们是单倍体。
Meiosis takes place in germ or sex cells called gametes; eggs in females and sperm in males.
减数分裂发生在称为配子的生殖细胞或性细胞中；雌性有卵子，雄性有精子。
Similar to mitosis, cells also pass through the Interphase, G1, S and G2 phase before they enter Meiosis.
与有丝分裂相似，细胞在进入减数分裂之前也经历了间期、G1、S和G2期。
Here are the distinct phases of meiosis: INTERPHASE MEIOSIS 1 CYTOKINESIS 1 MEIOSIS 2 CYTOKINESIS 2 .
减数分裂的不同阶段是：间期，减数分裂1，胞质分裂1，减数分裂2，胞质分裂2。
First at interphase
间期
In interphase, DNA is copied, resulting in two identical full sets of chromosomes to prepare for division.
在间期，DNA被复制，产生两组完全相同的染色体，为分裂做准备。
Outside of the nucleus are two centrosomes, each containing a pair of centrioles.
细胞核外有两个中心体，每个中心体包含一对中心粒。
These structures are critical for the process of cell division in next step at meiosis 1.
这些结构对减数分裂1的下一步细胞分裂过程至关重要。
Meiosis 1 takes place in following steps:
减数分裂1按以下步骤进行：
Prophase 1
前期1
Prophase 1 is typically the longest phase of meiosis.
前期1通常是减数分裂的最长时期。
During prophase 1, homologous chromosomes pair and exchange DNA (homologous recombination).
在前期1，同源染色体配对并交换DNA（同源重组）。
The new combinations of DNA created during crossover are a significant source of genetic variation, and result in new combinations of alleles, which may be beneficial.
在交换过程中产生的新的DNA组合是遗传变异的一个重要来源，并导致新的等位基因组合，这可能是有益的。
The paired and replicated chromosomes are called bivalents or tetrads, which have two chromosomes and four chromatids, with one chromosome coming from each parent.
配对和复制的染色体被称为二价体（也称为四分体），它们有两条染色体和四个染色单体，每个亲本都有一条染色体。
The process of pairing the homologous chromosomes is called synapsis.
同源染色体配对的过程称为联会。
At this stage, non-sister chromatids may cross-over at points called chiasmata (plural), (singular: chiasma).
在这个阶段，非姐妹染色单体可能会交叉。
Prophase 1 has historically been divided into a series of substages which are named according to the appearance of chromosomes.
前期1历来被分成一系列的亚阶段，根据染色体的外观来命名。
Leptotene
细线期
In this stage of prophase 1, individual chromosomes, each consisting of two sister chromatids, become "individualized" to form visible strands within the nucleus.
细线期在前期1的这一阶段，单个染色体，每个染色体由两个姐妹染色单体组成，变得“个体化”，在细胞核内形成可见的染色体丝。
Leptotene is of very short duration and it's when their progressive condensation and coiling of chromosome fibers takes place.
细线期的持续时间很短，这是染色体纤维逐渐凝结和卷曲的过程。
Zygotene
偶线期
Chromosomes approximately line up with each other into homologous chromosome pairs through synaptonemal complex.
染色体通过联会复合体大致排列成同源染色体对。
The paired chromosomes are called bivalent or tetrad chromosomes.
成对的染色体称为二价体（也称为四分体）。
Pachytene
粗线期
This is the stage when homologous recombination, including chromosomal crossover (crossing over), occurs.
这是发生同源重组的阶段，包括染色体互换。
Non-sister chromatids of homologous chromosomes may exchange segments over regions of homology.
同源染色体的非姐妹染色单体可以在同源区域交换片段。
At the sites where exchange happens, chiasmata formed.
在发生交换的地方，形成了交叉。
Diplotene
双线期
The synaptonemal complex degrades and homologous chromosomes separate from one another a little.
联会复合体解体，同源染色体开始分离。
However, the homologous chromosomes of each bivalent remain tightly bound at chiasmata, the regions where crossing-over occurred.
然而，每个二价体的同源染色体仍然紧密结合在交叉部位，也就是发生交叉的区域。
The chiasmata remain on the chromosomes until they are at the transition to anaphase 1.
交叉保留在染色体上，直到它们过渡到后期1。
Diakinesis
终变期
It closely resembles prometaphase of mitosis; the nucleoli disappear, the nuclear membrane disintegrates into vesicles, and the meiotic spindle begins to form.
与有丝分裂的前期相似，核仁消失，核膜解体成小泡，开始形成纺锤体。
