Cell Cycle and Cell Division Test - 40

Sepals (VI) and petals (I), are parts of accessory whorls of a flower and serve to attract pollinators only. A stamen consists of anther (III) and filament (IV). Anther is a broad knob part of stamen, that contains two long and cylindrical microsporangia in its lobes. Carpel is the female part of flower, derived from central region of thalamus and consists of stigma (II), style (V) and ovary (VII). Ovary and anther, are site of meiosis in flower to produce microspore (pollen) and egg cell respectively. So, the correct answer is option E.

• The cell cycle includes a series of events, that take place in a cell which leads to the duplication of DNA and division of cells to form two daughter cells. 
• During the interphase or the initial phase, the cells grow in size, the DNA starts to duplicate.
  
• After that mitotic phase will start which is again divided into subphases.
• During the prophase of mitosis, the nuclear membrane dissolves followed by metaphase, anaphase, and telophase respectively. After telophase, karyokinesis will be completed while cytokinesis starts.
• With the completion of cytokinesis parent cell will be divided into two daughter cells.

So, the correct answer is option D.

Fertilisation of haploid egg with two sperms will make a zygote with 3n chromosomal count (3n DNA content). DNA replication during S phase of cell cycle will double the DNA content to 6n. Formation of three poles during mitosis will distribute 2n DNA to each pole thereby restoring the diploid condition. So, the daughter cells will have the diploid (2n) chromosomal count and would be indistinguishable from normal cells. So, the correct answer is option A.

Correct Option: A

Explanation:

• Crossing over or chromosomal crossover is the exchange of genetic material between homologous chromosomes.
• This process takes place during prophase I, of Meiosis. This is the cause of variation.

Prophase 1 is the first stage of meiosis where the chromosome becomes visible (dense , thick, coiled) in leptotene stage of prophase 1. Each chromosome has identical sister chromatids. Thus, the correct answer is option A.

G$$_1$$ and G$$_2$$ phases of the cell cycle are separated by S phase which in turn is marked by DNA replication. The process of DNA replication double the DNA content of a G$$_2$$ phase cell as compared to its respective G$$_2$$ phase cell. The duplicated DNA content is accommodated in two chromatids of the single chromosome, both G$$_1$$ and G$$_2$$ cells have the same number of centromeres and chromosomes. So, the correct answer is option B.

DNA polymerase can not synthesize DNA de novo and needs primer causing problem in replication of ends of the chromosomes. Telomeres are the structures present at the ends of linear eukaryotic chromosomes and have mostly guanine residues in one strand and cytosine in the complementary strand. The G-rich strand is longer leaving a region of single-stranded DNA of up to a few hundred nucleotides at the 3’ end which serves as a primer for its elongation by telomerase enzyme. Telomerase contains both RNA and protein components. The RNA component is150 nucleotides long and has about 1.5 copies of the appropriate CyAx telomere repeat which serves as a template for synthesis of the TxGy strand of the telomere of linear DNA. In absence of telomerase enzyme, telomeres won't get replicated and chromosome will get shorter with each cycle of replication.
So, the correct answer is option D.

Mitosis is the process of cell division wherein, the chromosomes in a cell gets separated to to form two identical cells with equal number of chromosomes. The process of mitosis goes through interphase, prophase, metaphase, Anaphase and telophase before entering cytokinesis. While the first phases are the preparatory phases of the chromosome thickening, the metaphase finds the chromosomes  lined in the center of the cell to be divided. During Anaphase, the chromosomes gets divided from the centeromere, thereby giving rise to equal number of chromosomes which tend to move up to the two poles of the cell. During telophase, the chromosomes would have reached the two poles or ends of the cell and is ready for the division of the nucleoplasm. Hence, during the anaphase and telophase, the cell with 54 chromosomes will double the number of chromosomes i.e., 108. So, the correct answer is option A.

During Anaphase the centromere of each chromosome is divided into two parts. In this way, each chromosome is divided into two chromatids or two daughter chromosomes. Both the chromatids of each chromosome begin to move towards the opposite pole. Thus option D is the correct answer.

$$G_1$$ phase of cell cycle includes doubling of all cellular components except chromosomes while $$G_2$$ phase follows S phase and prepares the cell for division. S phase of cell cycle includes DNA replication. A prophase cell has duplicated DNA content accommodated in two sister chromatids of each chromosome. Metaphase is the stage of alignment of chromosomes on an equatorial plate while completion of the separation of sister chromatids which are now present at the opposite poles of cell marks telophase. So, the correct answer is option A.