问题 问答题 简答题

玉米亲本自交系与杂交种间的性状相关性怎样?

答案

参考答案:

为了能更有效地选择亲本,并预见所组成的杂交种的特性,亲本自交系与杂交种性状间的相互关系,常可为育种工作提供参考。

(1)株高和穗位高度根据山东农学院研究结果,绝大多数杂交种的株高是超过其双亲中较高的亲本。通常高株×高株和高株×中株,所得的杂交种的株高最大,中株×矮株和矮株×矮株获得的杂交种,株高最矮;中株×高株和中株×中株杂交种的株高介于中间。杂交种的穗位高度,大多数是超过和倾向双亲中高穗位的亲本。

(2)生育期根据北京农业大学观察,两亲本生育期相同的,杂种的生育期往往早于双亲;生育期相同的两个晚熟自交系杂交,杂交种生育期缩短的生育期日数要比两个早熟的自交系组配的杂交种缩短的生育日数显著得多。双亲间生育期相差较大时,杂交种的生育期介于双亲之间,且多偏于较早熟的亲本。

(3)抗大、小斑病据山东农学院研究结果:大、小斑病的遗传,单交种的双亲中有一个自交系是抗病的,另一个亲本是轻感病或中感病,则杂交种中大多数是较抗病或轻感病;若另一个亲本是重感病的则杂交种中会出现相当多的中感病和重感病类型。因而在组配单交种时,双亲起码要有一个亲本是抗病的。

(4)叶数、穗数、粒行数、粒型和穗轴色这些性状在大多数情况下,单交种的相应性状介于两亲本之间。

单项选择题

The following questions present a sentence, part of which or all of which is underlined. Beneath the sentence, you will find five ways of phrasing the underlined part. The first of these repeats the original; the other four are different. If you think the original is best, choose the first answer; otherwise choose one of the others.

These questions test correctness and effectiveness of expression. In choosing your answer, follow the requirements of standard written English; that is, pay attention to grammar, choice of words, and sentence construction. Choose the answer that produces the most effective sentence; this answer should be clear and exact, without awkwardness, ambiguity, redundancy, or grammatical error.

Blues musician Paul "Poboy" Smith, born in Tupelo, Mississippi, in 1936, has since 1958 been a fixture on the southern blues scene after the release of his debut album in that year.()

A. Blues musician Paul "Poboy" Smith, born in Tupelo, Mississippi, in 1936, has since 1958 been a fixture on the southern blues scene after the release of his debut album in that year.

B. Being born in 1936 in Tupelo, Mississippi, blues musician Paul "Poboy" Smith released his debut album in 1958 and has been a fixture on the southern blues scene since then.

C. Born in Tupelo, Mississippi, in 1936, blues musician Paul "Poboy" Smith has been a fixture on the southern blues scene since the release of his debut album in 1958.

D. Having been a texture on the southern blues scene since 1958 when he released his debut album, Paul "Poboy" Smith is a blues musician who was born in 1936 in Tupelo, Mississippi.

E. Since the release of his debut album in 1958, blues musician Paul "Poboy" Smith has been a fixture on the southern blues scene; he was born in Tupelo, Mississippi in 1936.

选择题