Question

From the given statements, identify the wrong pair.
(I) Cell organelles are newly formed in ${}^{\prime }{G}_2^{\prime }$ phase of cell cycle.
(II) Doubling of chromosomes occur in 'S' phase of cell cycle.
(III)The nuclei formed after meiosis-I are haploid.
(IV)Terminalization occurs in Anaphase-I.

• A. I,III
• B. I,IV
• C. II,IV
• D. III,IV

Answer 1

Answer: (C)

The cyclic events that take place between two successive cell divisions is called the cell cycle. The major, biochemically and physiologically active phase of cell cycle is the interphase in which the cell prepares for the nest set of divisions.
There are three major phases of interphase:

• In post-mitotic gap (G₁), there is active protein synthesis, some organelles duplicate and the cell growth continues.
• In S-phase the DNA content is doubled, keeping the chromosome number unaltered. Histone synthesis also occurs at this phase.
• In pre-mitotic gap (G₂), there are active protein synthesis, which are needed for the cell division. Some organelles are formed in this phase as well.

Meiosis is a type of reductional division which has the following salient features:

• reduction of the chromosome number in meiosis-I (the diploid mother cell form 2 haploid cells)
• genetic recombination or crossing-over which causes new combinations of genes in prophase-I of meiosis-I

The prophase-I is the longest in meiosis-I. There are five sub-phases, leptotene > zygotene > pachytene > diplotene > diakinesis. In Leptotene, homologous chromosomes becomes distinct. They pair in zygotene in a process called synapsis. Crossing over takes place in pachytene between the non-sister chromatids of homologous pair. Chiasma formation take place in diplotene and finally, terminalization in diakinesis.