遗传变异 - 高级

What helps ensure the survival of a species?
::什么能帮助确保物种的生存?

Genetic variation. It is this variation that is the essence of evolution. Without genetic differences among individuals, "survival of the fittest" would not be likely. Everyone would be exactly the same. How would it be determined who could or would survive? Either all survive, or all perish.
::基因变异。 这种变异是进化的精髓。 没有个人之间的基因差异, “ 适者生存” 不太可能。 每个人都会完全一样。 如何决定谁能或能活下来? 要么全部生存下来, 要么全部灭亡。

Meiosis and Genetic Variation
::诊断和遗传变异

results in infinite possibilities of genetic variation. In other words, sexual reproduction results in offspring that are genetically unique. They differ from both parents and also from each other. This occurs through a number of mechanisms, including crossing-over, the independent assortment of during anaphase I, and random fertilization .
::换句话说,性生殖导致遗传上独一无二的后代,与父母和父母都不同,彼此也不同,这通过若干机制出现,包括跨边界、在第一阶段独立分类和随机授精。

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• When homologous chromosomes form pairs during prophase I of I, crossing-over can occur. Crossing-over is the exchange of genetic material between non-sister chromatids of homologous chromosomes. It results in new combinations of genes on each chromosome.
  ::当同种染色体在I期的第一阶段形成一对同种染色体时,可能发生交叉交叉。交叉是同种染色体的非姐妹染色体的异种染色体之间的基因材料交换。它导致每种染色体的基因新组合。
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• When divide during meiosis, homologous chromosomes are randomly distributed during anaphase I, separating and segregating independently of each other. This is called independent assortment . It results in gametes that have unique combinations of chromosomes.
  ::当介质分裂时,同族染色体在第一阶段随机分布,彼此分离和分离。这被称为独立的组合。它导致有独特的染色体组合的调子。
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• In sexual reproduction, two gametes unite to produce an offspring. But which two of the millions of possible gametes will it be? This is likely to be a matter of chance. It is obviously another source of genetic variation in offspring. This is known as random fertilization.
  ::在性生殖方面,两个调子结合产生后代。 但是,在几百万种可能的调子中,哪一个会是? 这很可能是偶然的。 这显然是后代遗传变异的另一个来源。 这被称为随机受孕。

All of these mechanisms working together result in an amazing amount of potential variation. Each human couple, for example, has the potential to produce more than 64 trillion genetically unique children. No wonder we are all different!
::所有这些机制一起工作,都产生了惊人的潜在差异,例如,每对人类夫妇都有可能产生64万亿多个基因独特的儿童。 难怪我们都不同!

Crossing-Over
::交叉

As mentioned above, crossing-over occurs during prophase I, and it is the exchange of genetic material between non-sister chromatids of homologous chromosomes. Recall during prophase I, homologous chromosomes line up in pairs, gene-for-gene down their entire length, forming a configuration with four chromatids, known as a tetrad . The process of pairing the homologous chromosomes is called synapsis . During synapsis, non-sister chromatids may cross-over at points called chiasmata. Within a chiasma , the genetic material from two non-sister chromatids actually intertwine around each other, and some material from non-sister chromatids switch chromosomes, that is, the material breaks off and reattaches at the same position on the homologous chromosome ( Figure  ). This exchange of genetic material can happen many times within the same pair of homologous chromosomes, creating unique combinations of . This process is also known as homologous recombination .
::如上文所述,在第一期期间,交叉交叉发生,这是同色染色体的非姐妹染色体之间基因材料的交换。在第一期期间,在同色色体的非姐妹染色体之间,回顾在一期期间,同色体染色体在对齐时,在整段期间,以基因换基因,形成四种染色体的组合,称为四色体。对齐同色体染色体的过程称为合成体。在合成期间,非姐妹染色体可能在称为恰斯马塔的点交叉。在一期期间,两种非姐妹染色体的遗传材料实际上相互串联,非姐妹染色体切变色体的一些材料在另一期之间,非姐妹染色体切染色体的切色体交换中,即材料断裂和重新配对在同质染色体(Figure )的同一位置上。基因材料的交换可以多次发生在同质色体染色体的一对配体中,这种基因材料的交换可以发生许多次。在奇思马内,两个非姐妹染色体的染色体的基因组之间,这种独特的结合也是已知的独特结合。

Independent Assortment and Random Fertilization
::独立组分和随机授肥

In humans, there are over 8 million configurations in which the chromosomes can line up during metaphase I of meiosis. It is the specific processes of meiosis, resulting in four unique haploid cells, that result in these many combinations. This independent assortment, in which the chromosome inherited from either the father or mother can sort into any gamete, produces the potential for tremendous genetic variation. This process underlies the chromosomal basis of inheritance. Gregor Mendel's findings and laws will be discussed in the Inheritance concepts, but essentially, his findings led to the of two laws of inheritance: the Law of Segregation and the Law of Independent Assortment . The Law of Segregation states that when any individual produces gametes, the copies of a gene separate so that each gamete receives only one copy (one allele) of that gene. The Law of Independent Assortment states that separate genes for separate traits are passed independently of one another from parents to offspring.
::在人类中,有800多万个染色体组合,这些染色体可以在第一级梅氏化的元阶段排成一行。这是梅氏化的具体过程,导致四个独特的杂交细胞,形成许多组合。这种独立的分类,从父亲或母亲继承下来的染色体可以分解成任何组合体,产生巨大的遗传变异的可能性。这一过程是染色体继承基础的基础。Gregor Mendel的发现和法律将在继承概念中讨论,但基本上,他的发现导致两项继承法:《隔离法》和《独立分类法》。《隔离法》规定,当任何个人产生调子时,一个基因的复制件可以分开,这样每个色谱只接收该基因的复制件(一个所有元素)。《独立分类法》规定,不同特性的分别基因将独立于父母传给后代。

Together with random fertilization, more possibilities for genetic variation exist between any two people than the number of individuals alive today. Sexual reproduction is the random fertilization of a gamete from the female using a gamete from the male. In humans, over 8 million (2 ²³ ) chromosome combinations exist in the production of gametes in both the male and female. Essentially, when the homologous pairs of chromosomes line up during metaphase I and then are separated at anaphase I, there are (2 ²³ ) possible combinations of maternal and paternal chromosomes. During random fertilization, a cell, with over 8 million possible chromosome combinations, fertilizes an egg cell, which also has over 8 million possible chromosome combinations. Together, there are over 64 trillion unique combinations, not counting the additional variation produced by crossing-over during prophase I. In other words, each human couple could produce a child with over 64 trillion unique chromosome combinations!
::与随机授精一起,在任何两个人之间都存在着比今天活人数量更多的基因变异的可能性。性生殖是使用男性的调子来随机施肥。在人类中,在生产调子的过程中,男女都存在800多万(223)色谱组合。基本上,当同质染色体在元阶段一期间排在一起,然后在第一阶段分离时,可能存在母体和父体染色体的组合(223)。在随机施肥过程中,一个细胞,可能存在800多万种染色体组合,对一个蛋细胞施肥,这还可能存在800多万种染色体组合。在共存在64万亿种独特的组合,并不计入在子阶段一中交叉交替产生的额外变异。换句话说,每对夫妇都可能产生一个孩子,有64万亿多种独特的染色体组合!

Mitosis vs. Meiosis
::Mitispis vs. Meisisi vs. Meisis( 缩缩缩图)

and meiosis are two types of , with dramatically different products. Mitosis begins with a diploid somatic cell and ends with two genetically identical diploid cells. Meiosis begins with a diploid cell and produces four haploid genetically unique cells that form gametes.
::迷魂病是两种类型,有截然不同的产品。 迷魂病从一个低脂的体格细胞开始,最后是两个遗传上相同的低脂细胞。 迷魂病从一个低脂细胞开始,生产出四个随机的遗传上独特的细胞,组成调子。

Summary
::摘要

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• Crossing-over, the independent assortment of chromosomes during anaphase I, and random fertilization all increase the genetic variation of a species.
  ::交叉、在第一阶段对染色体的独立分类以及随机授精都增加了物种的遗传变异。

Review
::回顾

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1. Define crossing-over in meiosis.
   ::界定流行病的跨边界问题。
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2. Describe how crossing-over, independent assortment, and random fertilization lead to genetic variation.
   ::说明跨边界、独立的分类和随机授精如何导致遗传变异。
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3. Describe how independent assortment relates to the laws of inheritance.
   ::说明独立等级与继承法的关系。
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4. Define chiasmata.
   ::定义 chasmata 。
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5. When does mitosis and meiosis occur?
   ::何时发生肾上腺素中毒和肾上腺素中毒?