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Cell Reproduction
Chromosomes
• rod-like structures made of DNA and protein
2 Kinds of proteins in chromosomes
A. histones- proteins that DNA wraps around,
helps hold shape of chromosome and allows
DNA to pack tightly
B. nonhistones- Do not aid in packing of
DNA, instead they control specific regions
of the DNA
Chromosomes
• Chromosomes consist of two identical
halves (each half is called a chromatid)
• Chromatids form when DNA makes a copy
of itself prior to cell division
• When the cell divides each new cell
receives one chromatid
Chromosomes
• Chromatids are held together by a
centromere
Chromosomes
• Prokaryote DNA consists of a single
chromosome that is attached to inside of
cell membrane
Chromosome Number
• Each species has a characteristic number
of chromosomes in each cell
Ex: Humans 46
Dogs
78
Adder’s tongue fern 1,262
Chromosome # has nothing to do with
complexity of organism
Types of Chromosomes
1. Sex chromosomes- determine sex of
organism (could carry other genes as
well)
-Human sex chromosomes are either X or Y
Females XX
Males XY
Types of Chromosomes
2. Autosomes- all other chromosomes in an
organism
-Of the 46 human chromosomes, 2 are sex
chromosomes, the other 44 are
autosomes
Types of Chromosomes
• Every cell of an organism produced by
sexual reproduction has 2 copies of each
autosome (one from each parent)
• The two copies of each chromosome are
called homologous chromosomessame shape and size and carry genes for
same trait
Karyotypes
• Picture of an individual’s chromosomes
(cells are treated with chemicals to start
mitosis, photos are taken during
metaphase, and pictures are cut out and
matched up)
Diploid vs. Haploid Cells
• Diploid cells- cells with two sets of
chromosomes (2n)
• Diploid cells have both chromosomes for
each pair as well as the sex chromosomes
• Diploid cells in humans have 23 pairs, or
46 chromosomes 2n = 46
Diploid vs. Haploid Cells
• Human gametes, or sex cells, are haploid
sperm- male gamete
egg- female gamete
• Haploid cells contain only one set of
chromosomes, n
• Have half the # of chromosomes as diploid
cells and only have one sex chromosome
Diploid vs. Haploid Cells
• When sperm and egg unite during
fertilization, first cell of new organism will
be diploid (2n)
• If gametes were not haploid, the new cell
would be 4n and not functional
Cell Division in Prokaryotes
• Binary fission- Division of prokaryotes into two
identical offspring cells
3 Stages
1. Chromosome makes a copy of itself
2. Cell grows until approximately 2X size of
original
3. Cell wall forms between two chromosomes
forming 2 new identical cells
Cell Division in Eukaryotes
• Cell Cycle- events that make up the life of
a cell
2 Main Parts:
A. Interphase-cell growth and DNA
replication
B. Mitosis- nuclear and cytoplasmic division
Interphase
• most of cell’s time spent in this part of cycle
A. G1- cell grows in size and carries on
metabolism
B. S- DNA is copied
C. G2- cell grows some more and prepares to
divide
• *Some cells enter G0 phase where they remain
and no longer grow or divide (Ex: nerve cells)
Mitosis
4 Stages of Mitosis
1.
2.
3.
4.
Prophase
Metaphase
Anaphase
Telophase
Prophase
• first and longest stage of mitosis
• chromatin coils into rod-shaped
chromosomes
• Nucleus disappears
• Centrioles move to opposite ends of cell
• Spindle begins to form
Metaphase
• double chromosomes become attached to
spindle by centromere
• chromosomes line up on mid-line or
equator of cell
Anaphase
• sister chromatids separate and move to
opposite poles of cell
Telophase
•
•
•
•
final stage of mitosis
chromosomes reach opposite poles
spindle disassembles
nuclear envelope reappears and
nucleolous forms
Cytokinesis
• Cytoplasm divides
**Different between plant and animal cells
In animal cells, cell membrane pinches in
midway between two poles creating a
cleavage furrow
Cytokinesis
• In plant cells, vesicles formed by golgi fuse
together at mid-line forming a cell plate
**Each cell formed by mitosis receives an
exact copy of original cell’s chromosomes
and approximately half of the parent cell’s
cytoplasm and organelles.