Chiasmata, the visible points of crossing over, become clearly visible during which sub-stage of Prophase I?
A. Zygotene
B. Diplotene
C. Leptotene
D. Pachytene
Answer: Option B
Solution (By JKSSB Mock Tests)
Chiasmata become clearly visible during the diplotene stage of Prophase I. While the actual exchange of genetic material (crossing over) occurs during the pachytene stage, the homologous chromosomes begin to repel each other and move apart in diplotene, remaining connected only at the sites of crossing over, which appear as X-shaped chiasmata. Exam tip: Pachytene = crossing over; Diplotene = chiasmata visible.
Explanation:
Streptomycin is an antibiotic produced by the bacterium Streptomyces griseus. Penicillin and cephalosporins are from fungi (Penicillium and Cephalosporium). Griseofulvin is a fungal antibiotic. Streptomycin is a broad-spectrum aminoglycoside, effective against gram-negative bacteria and Mycobacterium tuberculosis. It inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit.
Consider statements about vitamins: 1. Vitamin E acts as an antioxidant. 2. Vitamin K is synthesized by gut bacteria. 3. Vitamin C is essential for collagen synthesis. Which are correct?
Explanation:
Vitamin E (tocopherol) is a fat-soluble antioxidant that protects cell membranes from oxidative damage by free radicals. Vitamin K is partially synthesized by the symbiotic bacteria residing in the human intestine, contributing to the body's supply. Vitamin C (ascorbic acid) is a crucial cofactor for the enzymes prolyl and lysyl hydroxylase, essential for the synthesis and stabilization of collagen. All statements are correct.
Explanation:
DNA is primarily located in the nucleus of eukaryotic cells. It contains deoxyribose (not ribose), is double-stranded, and adenine pairs with thymine. Thus, D is correct.
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