Chapter 4: Cell CycleShort Questions with Answers

DNA replication: the DNA of each chromosome is copied, so each chromosome comes to consist of two sister chromatids. The chromosome number stays the same.

Anaphase. Spindle fibres pull the sister chromatids towards opposite poles.

In prophase I, non-sister chromatids of homologous chromosomes exchange segments at chiasmata. This creates new combinations of genes on chromosomes, so each gamete is unique and offspring differ from their parents.

They attach to the centromeres (kinetochores) of chromosomes, line them up at the equator in metaphase, and pull the sister chromatids to opposite poles in anaphase.

Animal cells: a furrow forms at the equator and a contracting ring of microfilaments pinches the cell in two. Plant cells: Golgi vesicles fuse in the middle to form a phragmoplast (cell plate) that grows outward.

Mitosis keeps the chromosome number the same (2n → 2n); meiosis halves it (2n → n).

Each spindle fibre pulls a single chromosome to its pole, so homologous chromosomes separate: one of each pair goes to each pole. Two haploid sets form; each chromosome still has two sister chromatids.

It duplicates; the two centrosomes move to opposite poles and make the spindle fibres (mitotic spindle) that move the chromosomes.

The two identical copies of a chromosome, made in S phase and joined at the centromere. In meiosis they separate in anaphase-II.

Animals like the sea star regenerate lost parts by forming new cells through mitosis in the cells of the remaining parts; mitosis gives identical cells, so the new part is like the old.

Cells that stop dividing and perform their specific functions are in G0. Neurons stay in G0 indefinitely, liver and kidney cells temporarily; epithelial cells do not enter G0.

About 200 trillion cells (the book's figure), all formed from a single zygote by millions of mitotic divisions with equal distribution of genetic material.

The series of events in a eukaryotic cell from its formation to its division into two daughter cells. Main phases: interphase and M (mitosis) phase.

G1 (first gap), S (synthesis) and G2 (second gap).

The cell grows further, makes proteins for division, checks and repairs DNA damage, and reorganizes its contents for mitosis.

The cell grows, works, replicates its DNA and prepares for division; it lasts about 90% of the cycle.

Division of a cell into two daughter cells with the same number of chromosomes as the parent; in somatic cells of eukaryotes.

The division of prokaryotes into two identical cells; its events differ from mitosis.

Karyokinesis is division of the nucleus; cytokinesis is division of the cytoplasm.

Chromatin condenses into chromosomes (two chromatids each); nuclear envelope and nucleolus break down; centrosomes move apart making spindle fibres.

The plate formed when chromosomes attached to spindle fibres arrange themselves along the equator of the cell.

Special proteins at the centromere where spindle fibres attach.

Plant cells have no centrosome; their spindle forms by aggregation of spindle fibres present in the cytoplasm.

New nuclear envelope forms around each set of chromosomes, nucleolus reforms, and chromosomes unfold into chromatin.

Growth, cell replacement, regeneration and asexual reproduction.

By budding: mitosis forms a mass of cells (bud) on its surface, which grows into a new Hydra.

Masses of cells formed by uncontrolled division when genes regulating mitosis mutate. Benign tumors stay in place; malignant tumors (cancer) invade other tissues.

The spreading of cancer cells from the original tumor to other tissues.

Cell division in which each daughter cell receives half the number of chromosomes of the parent; a diploid cell forms four haploid cells.

Diploid cells have chromosomes in homologous pairs (2n); haploid cells have half the number, no pairs (n).

Synapsis is the pairing of homologous chromosomes in prophase I; each pair (four chromatids) is a tetrad.

X-shaped structures where non-sister chromatids are zipped together; each is a site of crossing over.

Tetrads align along the equator; two spindle fibres from both poles attach with one pair of homologous chromosomes.

In both, sister chromatids separate and the chromosome number does not change in that division.

Gametes are haploid; their fusion at fertilization restores the diploid number in the zygote.

Failure of homologous chromosomes or sister chromatids to separate in meiosis, giving gametes with abnormal chromosome numbers.

Gametes in animals; spores in flowering plants.