Explain the significance of mitosis, and describe the process.
In mitosis, identical chromosomes are distributed to each pole of the cell, and a
nuclear envelope forms around each set.
, duplicated chromosomes, each composed of a pair of sister
chromatids, become visible with the microscope. The nucleolus disappears, the
nuclear envelope breaks down, and the
begins to form.
, the chromosomes are aligned on the
cell; the mitotic spindle is complete and the kinetochores of the sister chromatids
are attached by microtubules to opposite poles of the cell.
, the sister chromatids separate and move to opposite poles.
Each former chromatid is now a chromosome.
, a nuclear envelope re-forms around each set of chromosomes,
nucleoli become apparent, the chromosomes uncoil, and the spindle disappears.
Cytokinesis generally begins in telophase.
Differentiate between asexual and sexual reproduction.
Offspring produces by
usually have hereditary traits
identical to those of the single parent. Mitosis is the basis for asexual reproduction
in eukaryotic organisms.
, two haploid cells, or
, fuse to form a single
. In a sexual life cycle,
must occur before gametes can be
Explain the significance of meiosis, and diagram the process.
A diploid cell undergoing
completes two successive cell divisions,
yielding four haploid cells.
Meiosis I begins with
, in which the members of a homologous pair of
chromosomes physically join by the process of
during which homologous (nonsister)
chromatids exchange segments of DNA strands.
- each consisting of a pair of homologous chromosomes
held together by one or more
- line up on the
members of each pair of homologous chromosomes separate during meiotic
and are distributed to different nuclei. Each nucleus contains the
haploid number of chromosomes; each chromosome consists of two chromatids.
, the two chromatids of each chromosome separate, and one is
distributed to each daughter cell. Each former chromatid is now a chromosome.
Contrast mitosis and meiosis, emphasizing the different outcomes.
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.