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【正文】 。當(dāng)他還是大學(xué)生時(shí)就提出了物質(zhì)的粒子屬性。孟德?tīng)栠M(jìn)行了一系列周密安排的實(shí)驗(yàn)來(lái)證實(shí)遺傳的顆粒性。直到他去世后，他的理論才被理解和接受。Mendel39。s Classic ExperimentsMendel studied genetics through plantbreeding experiments with the garden pea, a plant species that is selffertilizing and breeds true (each offspring is identical to the parent in the trait of interest). To test the blending theory, he focused his research on seven distinct characters. Each of these characters, such as seed color and plant height, present only two, clearcut possibilities. 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.孟德?tīng)柾ㄟ^(guò)豌豆實(shí)驗(yàn)研究遺傳學(xué)，豌豆是自花授粉植物和純品系。為驗(yàn)證融合理論，他的研究主要集中在7個(gè)特征上。例如，種子顏色，植株高度，這些特征只有兩個(gè)明確的可能性。他記錄了產(chǎn)生的每一個(gè)子代類(lèi)型和數(shù)量，在雜交產(chǎn)生子2代。For each of the characters he studied, Mendel found that one trait was dominant while the other was recessive. In the second filial (F2) generation, the ratio of dominant to recessive was 3:1. Mendel deduced that this result was possible only if each individual possesses only two hereditary units, one from each parent. The units Mendel hypothesized are today known as alleles, alternative forms of genes. Genes are the basic units of heredity. 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. When an organism is heterozygous for a trait, the resulting phenotype for that trait expresses only the dominant , the organism’s phenotype—its physical appearance and propertiesdiffers from its genotype, which may include both a dominant and a recessive allele. A pictorial representation of all possible binations of a genetic cross is known as a Punnett square.對(duì)于每個(gè)特征而言，要么顯形，要么隱性。在子2代中顯形與隱性比為3∶1。只有在每個(gè)個(gè)體僅擁有兩個(gè)研究遺傳單元，并每個(gè)單元來(lái)自一個(gè)親代時(shí)，實(shí)驗(yàn)結(jié)果才成立。此遺傳單元就是今天共識(shí)的等位基因。兩個(gè)一樣的等位基因決定一個(gè)特征，稱(chēng)純合。相反，稱(chēng)雜合。當(dāng)生物是雜合時(shí)，它的表型由顯性基因決定。因此，生物的表型與基因型是不同的。旁納特方格可以陳列所有可能的遺傳組合。The results of Mendel39。s experiments on dominant and recessive inheritance let to Mendel39。s first law: the law of law states that for a given trait an organism inherits one allele from each parent. Together these alleles form the allele pair. When gametes are formed during meiosis, the two alleles bee separated (halving of chromosome number).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. The ratio of dominant phenotypes (if any) in the progeny makes clear whether the unknown genotype is heterozygous, homozygous dominant, or homozygous recessive. 分離定律，生物只遺傳父母本等位基因?qū)Φ囊粋€(gè)等位基因。減數(shù)分裂期形成配子時(shí)兩個(gè)等位基因分離。為驗(yàn)證此理論，他做了測(cè)交實(shí)驗(yàn)，即基因型未知的植物與純合的隱性基因植物雜交。子代顯性表型可以明確測(cè)得雜合基因或純合基因的基因型。Mendel39。s Ideas and the Law of independent AssortmentMendel also performed dihybrid crosses, which enabled him to consider how two traits are inherited relative to one another. This work let to the law of independent assortment, which states that the alleles of genes governing different characters are inherited independently. An apparent exception to Mendel39。s laws is inplete dominance, a phenomenon in which offspring of a cross exhibit a phenotype that is intermediate between those of the parents. However, inplete dominance reflects the fact that both alleles for the trait in question exert an effect on the phenotype. The alleles themselves remain separate. 雙因子雜合試驗(yàn)，兩個(gè)特征是如何相互影響遺傳的。試驗(yàn)結(jié)果產(chǎn)生獨(dú)自分配定律，即等位基因獨(dú)立遺傳。特例是，不完全顯性。子代的表型是父母本的中間類(lèi)型。不完全顯性說(shuō)明了兩個(gè)等位基因?qū)Ρ硇投加杏绊憽＃任换驎?huì)繼續(xù)分離。Mendel presented his ideas in 1866 in a scientific paper published by the Brunn Society for Natural History. Unfortunately, the meaning of his research was not understood by other scientists of the day. His work was rediscovered in 1900 by Carl Correns and Hugo de Vries. 1866年，孟德?tīng)栐谧匀皇飞习l(fā)表了他的科學(xué)論文，陳訴了他的觀點(diǎn)。不幸的是，他的研究不被當(dāng)時(shí)科學(xué)家接受。在1900年，他的著作再被發(fā)現(xiàn)利用。Chromosomes and Mendelian GeneticsSoon after Mendel39。s work was rediscovered, Walter Sutton and Theodor Boveri independently proposed that the hereditary units might be located on chromosomes. Experiments to prove this hypothesis were carried out by Thomas Hunt Morgan and his students at Columbia University, in research on the sex chromosomes of fruit flies. Morgan39。s studies were also the first exploration of sexlinked traits. It also led to the discovery in 1916 by Calvin Bridges of the phenomenon of nondisjunction, in which a chromosome pair fails to segregate during meiosis.孟德?tīng)栔鞅辉侔l(fā)現(xiàn)不久，Walter Sutton 和Theodor Boveri提出，遺傳單位可能定位在染色體組上。伴性遺傳又導(dǎo)致了不分離現(xiàn)象的發(fā)現(xiàn)，即在減數(shù)分裂中，染色體對(duì)不分離。第五課Genes Code for Particular ProteinsThe first scientist to investigate the question of how genes affect phenotype was Sir Archibald Garrod, whose studies of alkaptonuria implied a relationship between genes and enzymes.Thirty years later Beadle and Ephrussi showed a relationship between particular genes and biosynthetic reactions responsible for eye color in fruit flies. Next, in a series of classic experiments on the effects of mutations in the bread mold Neurospora crassa, Beadle and Tatum explored the onegeneoneenzyme hypothesisthe idea that each gene codes for a particular enzyme.Their work paved the way for other researchers to elucidate the precise ways in which enzymes affect plex metabolic 1949, in research on the role of hemoglobin in sickle cell anemia, Linus Pauling helped refine the onegeneoneenzyme hypothesis into the onegeneonepolypeptide hypothesis.Archibald Garrod是第一個(gè)研究基因是如何影響表型的科學(xué)家，他對(duì)尿黑酸癥的研究揭示了基因與酶之間的關(guān)系。Beadle 和Ephrussi在三十年后對(duì)果蠅眼睛顏色的研究發(fā)現(xiàn)特殊基因與相關(guān)反應(yīng)的生物合成有關(guān)。接著對(duì)面包發(fā)霉粗糙脈孢菌的突變?cè)囼?yàn)得出一個(gè)基因一個(gè)酶的假說(shuō)。他們的工作為其他工作者鋪平了道路，即精確地闡明了酶影響了復(fù)雜的新陳代謝途徑。在1949年，對(duì)鐮刀狀細(xì)胞貧血癥的研究對(duì)一個(gè)基因一個(gè)酶的假說(shuō)進(jìn)一步上升為一個(gè)基因一個(gè)多肽。The Search for the Chemistry and Molecular Structure of nucleic AcidsNuclei acid, originally isolated by Johann Miescher in 1871, was identified as a prime constituent of chromosomes through the use of the redstaining method developed by Feulgen in the early 1900s.Frederick Griffith39。s experiments with the R and S stains of pneumococci showed that an as yet unknown material from one set of bacterial could a