Chromosomes, Mitosis and Meiosis

Question 1

Chromosomes constitution

Answer 1

Genes are informational units made of DNA. In Eukaryotes, DNA associates with protein to form chromatin fibers that make up chromosomes.

Question 2

How is DNA packed into chromosomes?

Answer 2

In eukaryotic cells DNA is associated with histones to form nucleosomes, each of which consists of a histone bead with DNA wrapped around it. Nucleosomes are organized into large, coiled loops held together by nonhistone scaffolding proteins.

Question 3

The cell cycle consists of…

Answer 3

Interphase and M phase.

Question 4

Interphase consists of

Answer 4

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

Question 5

G1 phase (Int)

Answer 5

During this phase the cell grows and prepares for the S phase.

Question 6

S phase (Int)

Answer 6

During the S phase DNA and the chromosome proteins are synthesized and chromosome duplication occurs.

Question 7

G2 phase (Int)

Answer 7

Protein synthesis increases in preparation for cell division.

Question 8

M phase

Answer 8

It consists of mitosis, the nuclear division that produces two nuclei identical to the parental nucleus, and cytokinesis, the division of the cytoplasm to yield two daughter cells.

Question 9

The structure of a duplicated chromosome (via mitosis)

Answer 9

It consists of a pair of sister chromatids which contain identical DNA saquences. Each chromatid includes a constricted region called a centromere. Sister chromatids are tightly associated in the region of their centromeres. Attached to each centromere is a kinetochore, a protein structure to which microtubules can bind.

Question 10

Mitosis significance

Answer 10

It assures that the chromosome number is preserved when one eukaryotic cell divides to form two. Identichal chromosomes are distributed to each pole of the cell.

Question 11

Prophase (mit1)

Answer 11

The structure of the duplicated chromosomes becomes apparent as the chromatin condenses; each is composed of a pair of identical sister chromatids. The nuclear envelope begins to disassemble, and the mitotic spindle begins to form.

Question 12

Prometaphase (mit2)

Answer 12

Spindle microtubules attach to kinetochores of chromosomes and they begin to move toward the cell’s midplane.

Question 13

Metaphase (mit3)

Answer 13

The chromosomes are aligned on the cell’s mid plane or metaphase plate; the mitotic spindle is complete and the kinetochores of the sister chromatids are attached by microtubules to opposite poles of the cell.

Question 14

Anaphase (mit4)

Answer 14

The sister chromatids separete and move to opposite poles. Each former chromatid is now a chromosome.

Question 15

Telophase (mit5)

Answer 15

A nuclear envelope re-forms around each set of chromosomes, nucleoli become apparent, the chromosomes uncoil, and the spindle disappears. Cytokinesis generally begins here.

Question 16

Cyclin-dependent kinases (Cdks) function

Answer 16

They are protein kinases involved in regulating the cell cycle.

Question 17

Asexual reproduction

Answer 17

Offspring produced like this usually have hereditary traits identical to those of the single parent. Mitosis is the basis for asexual reproduction in eukaryotic organisms.

Question 18

Asexual reproduction

Answer 18

Two haploid sex cells, or gametes, fuse to form a diploid zygote. In sexual life cycle, meiosis must occur before gametes can be produced.

Question 19

Diploid cells

Answer 19

They have a characteristic number of chromosome pairs per cell. The members of each pair, called homologous chromosomes, are similar in lenght, shape, and other features and carry genes affecting the same kinds of attributes of the organim.

Question 20

Haploid cells

Answer 20

They contain only one member of each homologous chromosome pair.

Question 21

Significance of meiosis

Answer 21

A diploid cell undergoing meiosis completes two succesive cell divisions, yielding four haploid cells. Sexual life cycles in eukaryotes require meiosis, which makes it possible for each gamete to contain only half the number of chromosomes in the parent cell.

Question 22

Meiosis I

Prophase

Answer 22

The members of a homologous pair of chromosomes physically join by the process of synapsis. Crossing-over is a process of genetic recombination during which homologous (nonsister) chromatids exchange segments of DNA strands.

Question 23

Meiosis I

metaphase I

Answer 23

Tetrads -each consisting of a pair of homologous chromosomes held together by one or more chiasmata- line up on the metaphase plate.

Question 24

Meiosis I

Anaphase I

Answer 24

The members of each pair of homologous chromosomes separate during anaphase I anda are distributed to different nuclei. Each nucleus contains the haploid number of chromosomes; each chromosome consists of two chromatids.

Question 25

Meiosis II

Answer 25

The two chromatids of each chromosome separate, and one is distributed to each daughter cell. Each former chromatid is now a chromosome.

Question 26

Contrast mitosis and meiosis

Answer 26

Mitosis involves a single nuclear division in which the two daughter cells formed are genetically identical to each other and to the original cell. Synapsis of homologous chromosomes does not occur during mitosis.
Meiosis involves two successive nuclear divisions and forms four haploid cells. Synapsis of homologous chromosomes occurs during prophase I of meiosis.

Question 27

Diploid and haploid cells, where?

Answer 27

Somatic cells of animals are diploid and are produced by mitosis. The only haploid cells are gametes, produced by gametogenesis, which in animals occurs by meiosis.