不同民族和种族之间的疾病发病率和死亡率可有明显差异，这种分布差异主要原因有

移码突变(frameshift mutant)

防突变浓度(mutant prevention concentration)

同源异型突变体(homeotic mutant)

超阻遏物突变体(superrepressor mutant)

A mutant of E. coli with a heat-sensitive DNA ligase (25℃ permissive, 37℃ nonpermissive) has been used to show that DNA synthesis is discontinuous. Examination of DNA replication in the presence of [3H]-thymidine in the mutant would demonstrate which of following？

A、The accumulation of short segments of unlabeled DNA at 25℃ and at 37℃.

B、The accumulation of short segments of unlabeled DNA at 25℃ but not at 37℃.

C、The accumulation of short segments of radioactive DNA at 37℃ but not at 25℃.

D、The incorporation of short fragments of radioactive DNA into longer ones at 25℃ and at 37℃.

A、homozygote for the dominant allele

B、homozygote for the recessive allele

C、heterozygote

D、mutant

E、inbred recessive

A．100%

B．0%

C．25%

D．50%

A、an allele that confers a phenotype on the organism when heterozygous; that is, when present in only one copy

B、an allele that confers a phenotype only when both copies of the gene are mutant; that is, when homozygous

C、an allele that is commonly found in wild populations, as opposed to alleles found in laboratory strains or when a pathological condition is present

D、an allele that confers a normal phenotype under some conditions, but confers a different, mutant phenotype when conditions such as elevated temperature are present