Cell division: mitosis and meiosis

BIOS 170

Cell Division: Mitosis and Meiosis

CHROMOSOME:

Between divisions the chromosome is a threadlike strand.
During interphase the chromosome replicates and becomes 2 thread like strands.

Homologous Chromosomes:

Pairs of chromosomes similar in size, shape, & genetic information, but not identical.

When both members of each pair are present, the cell is diploid (2n).
When only one member of the pair is present, the cell is haploid (n).
Humans:

diploid (2n) = 46
haploid (n) = 23

Recent cytokinesis

MITOSIS

The equal division of all cellular components to form two daughter cells that are identical to the original cell.
Ensures the same number and kind of chromosomes as the original cell. This is accomplished by replicating the DNA prior to cell division.
Original cell and daughter cells are all diploid.
Functions in asexual reproduction
Basis for growth in multi-celled organisms
Occurs in somatic cells found throughout the body.

MITOSIS (white fish)	MITOSIS (onion)
Interphase	Interphase
Prophase	Prophase
Metaphase	Metaphase
Anaphase	Anaphase
Telophase	Telophase

MITOSIS	MEIOSIS
Functions in growth and asexual reproduction.	Functions in sexual reproduction in multi-celled organisms.
Occurs in somatic cells found throughout the body.	Occurs in germ cells, located in testes or ovaries.
Produces clones, or exact replicates of the cell.	Produces haploid cells, or gametes, with the genetic material halved. When the gametes (eggs & sperm) fuse in fertilization the diploid # is restored.
Occurs in one division.	Requires two divisions.

Watch a NOVA Online Animation

How Cells Divide: Mitosis vs. Meiosis

Meiosis oogenesis in Ascaris
Primary oocyte with sperm nucleus	Secondary oocyte in late anaphase II or early telophase II
Primary oocyte with intact spermatozoan	Ovum where two polar bodies are visible
Primary oocyte in metaphase I	Ovum with male and female pronuclei
Primary oocyte in late anaphase I or early telophase I	Ovum with male and female pronuclei beginning to unite chromosomes
Secondary oocyte in metaphase II	Zygote undergoing mitosis in metaphase
Secondary oocyte and first polar body in metaphase II	Zygote undergoing mitosis in anaphase
Secondary oocyte in early anaphase II	Zygote undergoing mitosis in telophase

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