Concept 12.1: Most cell division results in genetically identical daughter cells

Question 1

The reproduction of a cell, with all of its complexity, cannot occur by a mere pinching in half; a cell is not like a soap bubble that simply

Answer 1

enlarges and splits in two.

Question 2

In both prokaryotes and eukaryotes, most cell division involves the distribution of

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identical genetic material—DNA—to two daughter cells.

Question 3

The exception is ____________, the special type of eukaryotic cell division that can produce sperm and eggs

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meiosis

Question 4

A dividing cell replicates its DNA, distributes the two copies to opposite ends of the cell, and then splits into

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daughter cells.

Question 5

A cell’s DNA, its genetic information, is called its

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genome.

Question 6

Although a prokaryotic genome is often a single DNA molecule, eukaryotic genomes usually consist of a

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number of DNA molecules

Question 7

A typical human cell, for example, has about 2 m of DNA—a length about

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250,000 times greater than the cell’s diameter.

Question 8

Before the cell can divide to form genetically identical daughter cells, all of this DNA must be

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copied, or replicated, and then the two copies must be separated so that each daughter cell ends up with a complete genome

Question 9

The replication and distribution of so much DNA are manageable because the DNA molecules are packaged into structures called

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chromosomes

Question 10

so named because they take up certain dyes used in

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microscopy

Question 11

Each eukaryotic chromosome consists of

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one very long, linear DNA molecule associated with many proteins

Question 12

The DNA molecule carries several hundred to a few thousand genes, the units of information that specify an organism’s

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inherited traits.

Question 13

The associated proteins maintain the structure of the chromosome and help control the activity of the

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genes.

Question 14

Together, the entire complex of DNA and proteins that is the building material of chromosomes is referred to as

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chromatin

Question 15

the chromatin of a chromosome varies in its degree of condensation during the process of

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cell division.

Question 16

Every eukaryotic species has a characteristic number of chromosomes in each

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cell’s nucleus.

Question 17

any cell in a multicellular organism except a sperm or egg or their precursors

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somatic cells

Question 18

the nuclei of human somatic cells (all body cells except the reproductive cells) each contain

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46 chromosomes, made up of two sets of 23, one set inherited from each parent

Question 19

a haploid reproductive cell, such as an egg or sperm that is formed by meiosis or is the descendent of cells formed by meiosis

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gamete

Question 20

Reproductive cells, or gametes—such as sperm and eggs—have half as many chromosomes as

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somatic cells; in our example, human gametes have one set of 23 chromosomes. 18 in cabbage plants, 48 in chimpanzees, 56 in elephants, 90 in hedgehogs, and 148 in one species of alga.

Question 21

When a cell is not dividing, and even as it replicates its DNA in preparation for cell division, each chromosome is in the form of a long, thin

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chromatin fiber.

Question 22

After DNA replication, however, the chromosomes condense as a part of cell division: Each chromatin fiber becomes

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densely coiled and folded, making the chromosomes much shorter and so thick that we can see them with a light microscope.

Question 23

Each duplicated chromosome consists of ________________________, which are joined copies of the original chromosome

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twosisterchromatids

Question 24

The two chromatids, each containing an identical DNA molecule, are typically attached all along their lengths by protein complexes called

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cohesins;

Question 25

this attachment is known as

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sister chromatid cohesion.

Question 26

Each sister chromatid has a _______________, a region made up of repetitive sequences in the chromosomal DNA where the chromatid is attached most closely to its sister chromatid

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centromere

Question 27

This attachment is mediated by proteins that ;

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recognize and bind to the centromeric DNA

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other bound proteins condense the DNA, giving the duplicated chromosome a narrow

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“waist.”

Question 29

The portion of a chromatid to either side of the centromere is referred to as an

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arm of the chromatid. (An unduplicated chromosome has a single centromere, distinguished by the proteins that bind there, and two arms.)

Question 30

Later in the cell division process, the two sister chromatids of each duplicated chromosome

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separate and move into two new nuclei, one forming at each end of the cell

Question 31

Once the sister chromatids separate, they are no longer called sister chromatids but are considered

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individual chromosomes; this is the step that essentially doubles the number of chromosomes during cell division.

Question 32

Thus, each new nucleus receives a collection of chromosomes identical to that of the

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parent cell.

Question 33

______________ the division of the genetic material in the nucleus, is usually followed immediately by ____________, the division of the cytoplasm. One cell has become two, each the genetic equivalent of the parent cell.

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Mitosis, cytokinesis

Question 34

a soccer players knee will be as good as new in a few weeks thanks to

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mitosis,

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mitosis, a type of cell division that generates

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new cells for growth and repair

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before a cell can divide, it must first

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duplicate the chromosomes stored in its nucleus

Question 37

during chromosome duplication, several bubbles open up open along the

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chromosome

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each bubble grows until it merges with an adjacent

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bubble

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each chromosome now consists of

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two identical copies called sister chromatids

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we see that each sister chromatids consists of

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DNA wound around small proteins called histones

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From a fertilized egg, mitosis and cytokinesis produced the

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200 trillion somatic cells that now make up your body, and the same processes continue to generate new cells to replace dead and damaged ones.

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you produce gametes—eggs or sperm—by a variation of cell division called meiosis, which yields

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daughter cells with only one set of chromosomes, half as many chromosomes as the parent cell.

Question 43

Meiosis in humans occurs only in special cells in the

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ovaries or testes (the gonads).

Question 44

Generating gametes, meiosis reduces the chromosome number from 46 (two sets) to

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23 (one set).

Question 45

Fertilization fuses two gametes together and returns the chromosome number to

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46 (two sets).

Question 46

Mitosis then conserves that number in every

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somatic cell nucleus of the new human individual.