Biology Exam Preparations - Questions and Answers

76 Epistasis implies

A one pair of genes can completely mask the expression of another pair of gene

B one pair of genes independently controls a particular phenotype

C one pair of genes enhances the phenotype expression of another pair of gene

D many genes collectively control a particular phenotype

Answer: Option [A]
Epistasis implies one pair of genes can completely mask the expression of another pair of gene. Epistasis is a phenomenon that consists of the effect of one gene being dependent on the presence of one or more modifier genes. A gene masks the effect of another gene. The interactions of the two genes which control comb type was revealed because we could identify and recognize the 9:3:3:1. Other genetic interactions were identified because the results of crossing the dihybrids produced a modified Mendelian ratio. All of the results are modifications of the 9:3:3:1 ratio.

77 Whereas the number of chromosomes is reduced to half in first reduction division of meiosis, then what is the need for second mitotic division?

A for the segregation of replicated chromosomes

B for equal distribution of haploid chromosomes

C for the formation of four gametes

D for the equal distribution of genes on chromosomes

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Answer: Option [A]
The correct answer is for the segregation of replicated chromosomes. The meiosis has two stages of division, meiosis I & meiosis II which are reductional & equational divisions respectively. The first meiotic division leads to the reduction of the chromosome number to half i.e haploid condition, the second meiotic division results in the formation of four different daughter cells which are haploid in number, it provides a physical basis for the law of segregation and independent assortment.

78 The polytene chromosomes were discovered for the first time in

A chironomus

B homozygous

C drosphila

D housefly

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Answer: Option [A]
The polytene chromosomes were discovered for the first time in chironomus. Polytene chromosomes were first observed in the salivary glands of Chironomous larva and hence called salivary gland chrorn.

79 The point at which the polytene chromosomes appera to be attached together is known as

A centricle

B chromocentre

C centromere

D chromomere

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Answer: Option [B]
The point at which the polytene chromosomes appera to be attached together is known as chromocentre. Chromocenter is the point at which polytene chromosomes appear to be attached together. Centriole is paired cellular organelle which functions in the organisation of the mitotic spindle during cell division in eukaryotes. Centromere is a specialised region on each chromatid to which kinetochores and sister chromatids attach. Chromomere is a small beadlike structure visible on a chromosome during prophase of meiosis and mitosis.

80 What is the chromosome number of plasmodium?

A 18

B 14

C 10

D 9

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Answer: Option [B]
The correct answer is 14. Plasmodium falciparum is a blood borne parasite which is responsible for human malaria. It has a 23 megabase genome that codes for approximately 5,300 genes. It has 14 chromosomes.