生物专业英语第三版蒋悟生编__课文翻译(17)

law of segregation 分裂定律

When gametes are formed by a diploid organism, the alleles that control a trait separate from one another into different gametes, retaining their individuality.

test cross 测交

A cross between a heterozygote of unknown genotype and an individual homozygous for the recessive genes in question

.dihybrid cross 双因子杂种，双因子杂合子

A cross between individuals that differ with respect to two specified gene pairs. law of independent assortment 独立分配定律，自由组合定律

Members of one gene pair will separate from each other independently of the members of other gene pairs.

incomplete dominance 不完全显性

The condition in which two allelic genes have a different effect when they are together as a heterozygote in a diploid cell than either of them have in the homozygous state

nondisjunction 不分离

The failure of separation of paired chromosomes at metaphase, resulting in one daughter receiving both and the other daughter cell none of the chromosomes in question. Nondisjunction can occur during a meiotic or mitotic division.

Discovering the Chemical Nature of the Gene

Genes Code for Particular Proteins

The 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 one-gene-one-enzyme hypothesis-the 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 complex metabolic pathways.In 1949, in research on the role of hemoglobin in sickle cell anemia, Linus Pauling helped refine the one-gene-one-enzyme hypothesis into the one-gene-one-polypeptide hypothesis.

Archibald Garrod是第一个研究基因是如何影响表型的科学家，他对尿黑酸症的研究揭示了基因与酶之间的关系。Beadle 和Ephrussi在三十年后对果蝇眼睛颜色的研究发现特殊基因与相关反应的生物合成有关。接着对面包发霉粗糙脉孢菌的突变试验得出一个基因一个酶的假说。他们的工作为其他工作者铺平了道路，即精确地阐明了酶影响了复杂的新陈代谢途径。在1949年，对镰刀状细胞贫血症的研究对一个基因一个酶的假说进一步上升为一个基因一个多肽。

The Search for the Chemistry and Molecular Structure of nucleic Acids

Nuclei acid, originally isolated by Johann Miescher in 1871, was identified as a prime constituent of chromosomes through the use of the red-staining method developed by Feulgen in the early 1900s. Frederick Griffith's experiments with the R and S stains of pneumococci showed that an as yet unknown material from one set of bacterial could alter the physical traits of a second set. In the 1940s the team of Avery, MacLeod, and McCarty showed that this unknown material was DNA. At about the same time P.A. Levene discovered that DNA contained four nitrogenous bases, each of which was attached to a sugar molecule and a phosphate group-a combination Levene termed a nucleotide.

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