Chromosomes, Mitosis and Meiosis Flashcards

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1
Q

Chromosomes constitution

A

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

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2
Q

How is DNA packed into chromosomes?

A

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.

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3
Q

The cell cycle consists of…

A

Interphase and M phase.

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4
Q

Interphase consists of

A

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

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5
Q

G1 phase (Int)

A

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

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6
Q

S phase (Int)

A

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

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7
Q

G2 phase (Int)

A

Protein synthesis increases in preparation for cell division.

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8
Q

M phase

A

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.

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9
Q

The structure of a duplicated chromosome (via mitosis)

A

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.

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10
Q

Mitosis significance

A

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.

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11
Q

Prophase (mit1)

A

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.

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12
Q

Prometaphase (mit2)

A

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

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13
Q

Metaphase (mit3)

A

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.

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14
Q

Anaphase (mit4)

A

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

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15
Q

Telophase (mit5)

A

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

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16
Q

Cyclin-dependent kinases (Cdks) function

A

They are protein kinases involved in regulating the cell cycle.

17
Q

Asexual reproduction

A

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.

18
Q

Asexual reproduction

A

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

19
Q

Diploid cells

A

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.

20
Q

Haploid cells

A

They contain only one member of each homologous chromosome pair.

21
Q

Significance of meiosis

A

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.

22
Q

Meiosis I

Prophase

A

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.

23
Q

Meiosis I

metaphase I

A

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

24
Q

Meiosis I

Anaphase I

A

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.

25
Q

Meiosis II

A

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

26
Q

Contrast mitosis and meiosis

A

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.

27
Q

Diploid and haploid cells, where?

A

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.