Consider statements about genetics: 1. Genes are located on chromosomes. 2. DNA replication is semi-conservative. 3. RNA is double-stranded. Which are correct? MCQ with Answer and Explanation

Question

Consider statements about genetics: 1. Genes are located on chromosomes. 2. DNA replication is semi-conservative. 3. RNA is double-stranded. Which are correct?

A. 1, 2 and 3

B. 2 and 3 only

C. 1 and 3 only

D. 1 and 2 only

Answer: Option D

Solution (By JKSSB Mock Tests)

Genes are specific sequences of DNA that code for proteins or RNA, and they are arranged linearly on chromosomes within the nucleus. DNA replication is semi-conservative, meaning each newly synthesized DNA molecule consists of one original parental strand and one newly synthesized strand, as proven by the Meselson-Stahl experiment. RNA is typically single-stranded, allowing it to fold into complex shapes and perform various functions, unlike the double-stranded DNA helix. Thus, statements 1 and 2 are correct.

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Question #1

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The disease caused by the deficiency of vitamin B₃ (niacin) is characterized by:

A. Night blindness

B. Bone deformities

C. Bleeding gums

D. Dermatitis, diarrhea, dementia

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Correct Answer: Option D

Explanation:
Pellagra (niacin deficiency) presents with the three D's: dermatitis, diarrhea, and dementia. Bleeding gums is scurvy (vitamin C), bone deformities rickets (vitamin D), night blindness vitamin A deficiency.

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Question #2

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Crossing over between homologous chromosomes occurs during which sub-stage of Prophase I in meiosis?

A. Zygotene

B. Leptotene

C. Diplotene

D. Pachytene

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Correct Answer: Option D

Explanation:
Prophase I of meiosis is divided into five sub-stages: leptotene, zygotene, pachytene, diplotene, and diakinesis. Crossing over, the exchange of genetic material between non-sister chromatids of homologous chromosomes, occurs specifically during the pachytene stage at structures called recombination nodules.

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Question #3

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Which of the following cell organelles is capable of self-replication?

A. Lysosome

B. Mitochondria

C. Rough endoplasmic reticulum

D. Golgi apparatus

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Correct Answer: Option B

Explanation:
Mitochondria and chloroplasts contain their own DNA and ribosomes (70S) and can replicate by binary fission, a feature supporting their endosymbiotic origin. Golgi apparatus, lysosomes, and rough ER cannot self-replicate; they are part of the endomembrane system and arise from pre-existing membranes. Mitochondria are thus semi-autonomous organelles.

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