Question

DNA duplication occurs in
A. Mitosis only
B. Meiosis only
C. Meiosis I and mitosis
D. Meiosis II and mitosis

Answer 1

Cell cycle represents the orderly and cyclic sequence of events, processes and phases between two successive cell divisions. During this process, cellular material gets doubled and almost equally distributed between the incipient daughter cells. The length of the cell cycle varies with different kinds of cells.

Complete step by step answer: Cell cycle involves a co-ordinated marshalling of several cellular events. Some of them are continuous and some others are discontinuous. Cell division is always coordinated with cell growth and DNA duplication so that the size and DNA content of cells remain constant.
A standard eukaryotic cell cycle consists of four non- overlapping linear phases, namely G1, S, G2 and M. G1 and G2 are the first and second gap phases during which DNA synthesis does not occur. S is a synthetic phase, characterised by active synthesis of DNA. M is the mitotic phase or division phase during which cell division occurs. G1, G2 and S collectively represent the non-dividing phase of the cell cycle, often called interphase.
Mitosis: It is the peculiar type of cell division, which ensures the biological continuity of organisms, maintains their genetic constancy and preserves their somatic chromosome value unchanged through successive generations. It is the terminal stage of the cell cycle of events. Essentially, mitosis involves two closely related processes, namely nuclear duplication and cytoplasmic cleavage, known as karyokinesis and cytokinesis respectively. These two are completed in a definite stage of the cell cycle called mitotic phase. The interval between the end of one mitotic cycle and the beginning of the next is called interphase. The mitotic phase is divided into five major stages, namely interphase, prophase, metaphase, anaphase and telophase. Duplication of DNA occurs in the S phase of interphase. So, DNA duplication occurs in mitosis.
Meiosis: Meiosis is specialised type of cell division, occurring in the diploid reproductive cells of all sexually reproducing organisms. It provides a mechanism for the reduction of chromosome number from a diploid to haploid value. so , it is often called reduction division. The overall meiotic cell cycle involves a single chromosomal duplication and two successive cell divisions.
The first meiotic cell division or meiosis I is reductional, disjunctional and heterotypic division. In this, the diploid chromosome complement of the parent cell is reduced to a haploid value in the daughter cells.
The second meiotic division or meiosis II is a homotypic and equational division, because the daughter cells are identical to each other and also to the immediate parent cell. Meiosis II is equivalent to mitosis.
Before the actual meiotic division, the cell undergoes active genetic and metabolic preparations. These preparations are called interphase. During this interphase, duplication of DNA occurs. Adjuscend to this process actual meiosis occurs, ie, meiosis I.
Thus, here the correct answer is C) Meiosis I and mitosis.

Note: Living organisms have the inherent ability to grow and reproduce. Growth and reproduction occur at cellular and organismal levels. Cellular growth is accomplished by the intake of substances and the intracellular synthesis of biomolecules. Cellular reproduction occurs by the production of new cells from pre-existing cells. It involves the synthesis of cell constituents, duplication of chromosomes, nucleus and cell organelles, such as golgi bodies, centrioles and mitochondria, microbodies and chloroplast, and the division of cells.