Concept 12.1: Most cell division results in genetically identical daughter cells Flashcards
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
enlarges and splits in two.
In both prokaryotes and eukaryotes, most cell division involves the distribution of
identical genetic material—DNA—to two daughter cells.
The exception is ____________, the special type of eukaryotic cell division that can produce sperm and eggs
meiosis
A dividing cell replicates its DNA, distributes the two copies to opposite ends of the cell, and then splits into
daughter cells.
A cell’s DNA, its genetic information, is called its
genome.
Although a prokaryotic genome is often a single DNA molecule, eukaryotic genomes usually consist of a
number of DNA molecules
A typical human cell, for example, has about 2 m of DNA—a length about
250,000 times greater than the cell’s diameter.
Before the cell can divide to form genetically identical daughter cells, all of this DNA must be
copied, or replicated, and then the two copies must be separated so that each daughter cell ends up with a complete genome
The replication and distribution of so much DNA are manageable because the DNA molecules are packaged into structures called
chromosomes
so named because they take up certain dyes used in
microscopy
Each eukaryotic chromosome consists of
one very long, linear DNA molecule associated with many proteins
The DNA molecule carries several hundred to a few thousand genes, the units of information that specify an organism’s
inherited traits.
The associated proteins maintain the structure of the chromosome and help control the activity of the
genes.
Together, the entire complex of DNA and proteins that is the building material of chromosomes is referred to as
chromatin
the chromatin of a chromosome varies in its degree of condensation during the process of
cell division.
Every eukaryotic species has a characteristic number of chromosomes in each
cell’s nucleus.
any cell in a multicellular organism except a sperm or egg or their precursors
somatic cells
the nuclei of human somatic cells (all body cells except the reproductive cells) each contain
46 chromosomes, made up of two sets of 23, one set inherited from each parent
a haploid reproductive cell, such as an egg or sperm that is formed by meiosis or is the descendent of cells formed by meiosis
gamete
Reproductive cells, or gametes—such as sperm and eggs—have half as many chromosomes as
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.
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
chromatin fiber.
After DNA replication, however, the chromosomes condense as a part of cell division: Each chromatin fiber becomes
densely coiled and folded, making the chromosomes much shorter and so thick that we can see them with a light microscope.
Each duplicated chromosome consists of ________________________, which are joined copies of the original chromosome
twosisterchromatids
The two chromatids, each containing an identical DNA molecule, are typically attached all along their lengths by protein complexes called
cohesins;
this attachment is known as
sister chromatid cohesion.
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
centromere
This attachment is mediated by proteins that ;
recognize and bind to the centromeric DNA
other bound proteins condense the DNA, giving the duplicated chromosome a narrow
“waist.”
The portion of a chromatid to either side of the centromere is referred to as an
arm of the chromatid. (An unduplicated chromosome has a single centromere, distinguished by the proteins that bind there, and two arms.)
Later in the cell division process, the two sister chromatids of each duplicated chromosome
separate and move into two new nuclei, one forming at each end of the cell
Once the sister chromatids separate, they are no longer called sister chromatids but are considered
individual chromosomes; this is the step that essentially doubles the number of chromosomes during cell division.
Thus, each new nucleus receives a collection of chromosomes identical to that of the
parent cell.
______________ 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.
Mitosis, cytokinesis
a soccer players knee will be as good as new in a few weeks thanks to
mitosis,
mitosis, a type of cell division that generates
new cells for growth and repair
before a cell can divide, it must first
duplicate the chromosomes stored in its nucleus
during chromosome duplication, several bubbles open up open along the
chromosome
each bubble grows until it merges with an adjacent
bubble
each chromosome now consists of
two identical copies called sister chromatids
we see that each sister chromatids consists of
DNA wound around small proteins called histones
From a fertilized egg, mitosis and cytokinesis produced the
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.
you produce gametes—eggs or sperm—by a variation of cell division called meiosis, which yields
daughter cells with only one set of chromosomes, half as many chromosomes as the parent cell.
Meiosis in humans occurs only in special cells in the
ovaries or testes (the gonads).
Generating gametes, meiosis reduces the chromosome number from 46 (two sets) to
23 (one set).
Fertilization fuses two gametes together and returns the chromosome number to
46 (two sets).
Mitosis then conserves that number in every
somatic cell nucleus of the new human individual.
