生物专业英语蒋悟生版本第四课
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当他还是只有数学背景的大学生时就提出了物质的粒 子属性，孟德尔进行了一系列周密安排的实验来证实 遗传的颗粒性。
His revolutionary ideas were neither understood nor accepted until many years after Mendel died.
在减数分裂期形成配子时，两个等位基因分离。 （染色体数目减半）
To gain evidence for his theory Mendel performed test crosses, mating plants of unknown genotype to plants that were homozygous recessive for the trait of interest. 为验证他的理论，孟德尔做了测交实验，即基因 型未知的植物与纯合的隐性基因植物杂交。
He also recorded the type and number of all progeny produced from each pair of parent pea plants, and followed the results of each cross for two generations.
An organism that inherits identical alleles for a trait from each parent is said to be homozygous for that trait; if different alleles for a trait are inherited, the organism is heterozygous for that trait. 一个生物体从每个亲本获得相同的等位基因， 称纯合子；如果获得不同的等位基因，称杂合 子。
直到孟德尔去世很多年以后，他的理论才 被理解和接受。
3. Mendel's Classic Experiments
Mendel studied genetics through plant-breeding experiments with the
garden pea, a plant species that is self-fertilizing and breeds true (each offspring is identical to the parent in the trait of interest). 孟德尔通过豌豆的植物育种实验研究遗传学，豌豆是自花授粉植 物和纯品系。（每个子代在遗传性状上与亲本是完全相同的）
This work led to the law of independent assortment, which states that the alleles of genes governing different characters are inherited independently.
Having been exposed to theories of the particulate nature of matter while a university student and having a background in mathematics, Mendel carried out a series of carefully planned experiments that demonstrated the particulate nature of heredity.
2. Gregor Mendel and the Birth of Genetics
Gregor Mendel, an Augustinian monk in the monastery at Brunn, Austria, is known as the "father of genetics." 孟德尔，一名奥地利，布伦修道院的奥古斯丁修道士，是 众所周知的遗传学之父。
To test the blending theory, he focused his research on seven distinct characters. 为验证融合理论，他的研究主要集中在7个显著的 特征上。 Each of these characters, such as seed color and plant height, present only two, clear-cut possibilities. 这些性状中的每一个，例如，种子颜色，植株高度， 只表现出两个明确的可能性。
他还记录了每一对亲本豌豆产生的所有个子代 的类型和数量，并且记录每对亲本杂交产生子2 代的结果。
For each of the characters he studied, Mendel found that one trait was dominant while the other was recessive.
4. Mendel's Ideas and the Law of independent Assortment
Mendel also performed dihybrid crosses, which enabled him to consider how two traits are inherited relative to one another. 孟德尔还进行了双因子杂合子杂交，这使他考虑到两 对相对性状是如何遗传的。
Lesson Four Foundations of Genetics
—— XX 班 XX
1.Early Theories of inheritance
Early ideas of inheritance included Hippocrates' theory of pangenesis and August Weismann‘s germ plasm
When an organism is heterozygous for a trait, the resulting phenotype for that trait expresses only the dominant allele. 当生物是杂合子时，它的表型由显性等位基因 决定。
Thus, the organism’s phenotype—its physical appearance and properties-differs from its genotype, which may include both a dominant and a recessive allele. 因此，生物的表型，其外观和特征，不同于它的基 因型，基因型可能既包括显性等位基因，又包括隐 性等位基因。
Together these alleles form the allele pair.
这些等位基因一起组成等位基因对。
When gametes are formed during meiosis, the two alleles become separated (halving of chromosome number).
这项工作产生了自由组合定律，表明控制不同 性状的等位基因是独立遗传的。
An apparent exception to Mendel‘s laws is incomplete dominance, a phenomenon in which offspring of a cross exhibit a phenotype that is intermediate between those of the parents. 孟德尔定律的一个特例是不完全显性，即一个交叉的 子代表现出一种介于亲本之间的表型的现象。
孟德尔的显性和隐性遗传实验的结果遵循孟德尔第一定律： 分离定律。
This law states that for a given trait an organism inherits one allele from each parent. 该定律指出，对于一种特定的性状，生物只遗传每 个亲本的一个等位基因。
However, incomplete dominance reflects the fact that both alleles for the trait in question exert an effect on the phenotype.
然而，不完全显性反映了一个事实，两个等位基因对 表型都有影响。 The alleles themselves remain separate.
The units Mendel hypothesized are today known as alleles, alternative forms of genes. 孟德尔假设的遗传单元就是现在称作的等位基因， 替代形式的基因。
Genes are theBaidu Nhomakorabeabasic units of heredity. 基因是遗传的基本单位。
对于他研究的每对性状，孟德尔发现，一个性状是显性的，而 另一个是隐性的。
In the second filial (F2) generation, the ratio of dominant to recessive was 3:1. 在子2代中，显性与隐性比为3∶1。
Mendel deduced that this result was possible only if each individual possesses only two hereditary units, one from each parent. 孟德尔推断，只有在每个个体仅拥有两个遗传 单元，并且每个单元来自一个亲代时，这种结 果才可能成立。
A pictorial representation of all possible combinations of a genetic cross is known as a Punnett square. 一个遗传交叉的所有可能组合的图形描述称为旁纳特方格。
The results of Mendel's experiments on dominant and recessive inheritance led to Mendel's first law: the law of segregation.
The ratio of dominant phenotypes (if any) in the progeny makes clear whether the unknown genotype is heterozygous, homozygous dominant, or homozygous recessive. 显性表型（如果有的话）在子代中的比例可以 明确测得未知基因型是否为杂合子、显性纯合 子或隐性纯合子。
theory.
遗传学的早期理论包括希波克拉底的泛生论和奥古斯特·魏斯曼的种 质理论。
Based on experiments with mice, Weismann proposed that hereditary information in gametes transmitted traits to progeny. 基于小鼠实验，魏斯曼提出配子中的遗传信息将性状 传递给后代。 Both of these early views incorporated the blending theory: they held that heritable traits of the two parents blend, so that the distinct characteristics of each are lost in offspring. 这两种早期观点合起来形成融合理论：他们认为两个 亲本的遗传性状混合，以至于每个亲本的鲜明特征在 子代中丢失。
His revolutionary ideas were neither understood nor accepted until many years after Mendel died.
在减数分裂期形成配子时，两个等位基因分离。 （染色体数目减半）
To gain evidence for his theory Mendel performed test crosses, mating plants of unknown genotype to plants that were homozygous recessive for the trait of interest. 为验证他的理论，孟德尔做了测交实验，即基因 型未知的植物与纯合的隐性基因植物杂交。
He also recorded the type and number of all progeny produced from each pair of parent pea plants, and followed the results of each cross for two generations.
An organism that inherits identical alleles for a trait from each parent is said to be homozygous for that trait; if different alleles for a trait are inherited, the organism is heterozygous for that trait. 一个生物体从每个亲本获得相同的等位基因， 称纯合子；如果获得不同的等位基因，称杂合 子。
直到孟德尔去世很多年以后，他的理论才 被理解和接受。
3. Mendel's Classic Experiments
Mendel studied genetics through plant-breeding experiments with the
garden pea, a plant species that is self-fertilizing and breeds true (each offspring is identical to the parent in the trait of interest). 孟德尔通过豌豆的植物育种实验研究遗传学，豌豆是自花授粉植 物和纯品系。（每个子代在遗传性状上与亲本是完全相同的）
This work led to the law of independent assortment, which states that the alleles of genes governing different characters are inherited independently.
Having been exposed to theories of the particulate nature of matter while a university student and having a background in mathematics, Mendel carried out a series of carefully planned experiments that demonstrated the particulate nature of heredity.
2. Gregor Mendel and the Birth of Genetics
Gregor Mendel, an Augustinian monk in the monastery at Brunn, Austria, is known as the "father of genetics." 孟德尔，一名奥地利，布伦修道院的奥古斯丁修道士，是 众所周知的遗传学之父。
To test the blending theory, he focused his research on seven distinct characters. 为验证融合理论，他的研究主要集中在7个显著的 特征上。 Each of these characters, such as seed color and plant height, present only two, clear-cut possibilities. 这些性状中的每一个，例如，种子颜色，植株高度， 只表现出两个明确的可能性。
他还记录了每一对亲本豌豆产生的所有个子代 的类型和数量，并且记录每对亲本杂交产生子2 代的结果。
For each of the characters he studied, Mendel found that one trait was dominant while the other was recessive.
4. Mendel's Ideas and the Law of independent Assortment
Mendel also performed dihybrid crosses, which enabled him to consider how two traits are inherited relative to one another. 孟德尔还进行了双因子杂合子杂交，这使他考虑到两 对相对性状是如何遗传的。
Lesson Four Foundations of Genetics
—— XX 班 XX
1.Early Theories of inheritance
Early ideas of inheritance included Hippocrates' theory of pangenesis and August Weismann‘s germ plasm
When an organism is heterozygous for a trait, the resulting phenotype for that trait expresses only the dominant allele. 当生物是杂合子时，它的表型由显性等位基因 决定。
Thus, the organism’s phenotype—its physical appearance and properties-differs from its genotype, which may include both a dominant and a recessive allele. 因此，生物的表型，其外观和特征，不同于它的基 因型，基因型可能既包括显性等位基因，又包括隐 性等位基因。
Together these alleles form the allele pair.
这些等位基因一起组成等位基因对。
When gametes are formed during meiosis, the two alleles become separated (halving of chromosome number).
这项工作产生了自由组合定律，表明控制不同 性状的等位基因是独立遗传的。
An apparent exception to Mendel‘s laws is incomplete dominance, a phenomenon in which offspring of a cross exhibit a phenotype that is intermediate between those of the parents. 孟德尔定律的一个特例是不完全显性，即一个交叉的 子代表现出一种介于亲本之间的表型的现象。
孟德尔的显性和隐性遗传实验的结果遵循孟德尔第一定律： 分离定律。
This law states that for a given trait an organism inherits one allele from each parent. 该定律指出，对于一种特定的性状，生物只遗传每 个亲本的一个等位基因。
However, incomplete dominance reflects the fact that both alleles for the trait in question exert an effect on the phenotype.
然而，不完全显性反映了一个事实，两个等位基因对 表型都有影响。 The alleles themselves remain separate.
The units Mendel hypothesized are today known as alleles, alternative forms of genes. 孟德尔假设的遗传单元就是现在称作的等位基因， 替代形式的基因。
Genes are theBaidu Nhomakorabeabasic units of heredity. 基因是遗传的基本单位。
对于他研究的每对性状，孟德尔发现，一个性状是显性的，而 另一个是隐性的。
In the second filial (F2) generation, the ratio of dominant to recessive was 3:1. 在子2代中，显性与隐性比为3∶1。
Mendel deduced that this result was possible only if each individual possesses only two hereditary units, one from each parent. 孟德尔推断，只有在每个个体仅拥有两个遗传 单元，并且每个单元来自一个亲代时，这种结 果才可能成立。
A pictorial representation of all possible combinations of a genetic cross is known as a Punnett square. 一个遗传交叉的所有可能组合的图形描述称为旁纳特方格。
The results of Mendel's experiments on dominant and recessive inheritance led to Mendel's first law: the law of segregation.
The ratio of dominant phenotypes (if any) in the progeny makes clear whether the unknown genotype is heterozygous, homozygous dominant, or homozygous recessive. 显性表型（如果有的话）在子代中的比例可以 明确测得未知基因型是否为杂合子、显性纯合 子或隐性纯合子。
theory.
遗传学的早期理论包括希波克拉底的泛生论和奥古斯特·魏斯曼的种 质理论。
Based on experiments with mice, Weismann proposed that hereditary information in gametes transmitted traits to progeny. 基于小鼠实验，魏斯曼提出配子中的遗传信息将性状 传递给后代。 Both of these early views incorporated the blending theory: they held that heritable traits of the two parents blend, so that the distinct characteristics of each are lost in offspring. 这两种早期观点合起来形成融合理论：他们认为两个 亲本的遗传性状混合，以至于每个亲本的鲜明特征在 子代中丢失。