Download Chapter 8 – Cell Reproduction

Mitosis and Meiosis
The continuity of life is based on
the reproduction of cells, or cell
division.
Cell Reproduction
• Two types of cell division in eukaryotic
cells: one called mitosis and the other
meiosis
• Cell division in prokaryotic (bacteria) cells:
is called binary fission
• Words of Wisdom: Understand the
process, and you will understand the
words.
Key Ideas
• Question: Why do cells divide?
• Question: How do cells divide?
Why don’t cells get giant?
• Remember cell membranes?
– Input of nutrients and gets rid of wastes.
• Think about Geometry…volume of a cube
is going to increase faster than the surface
area. The cell membrane is a surface
area issue.
Dividing a Eukaryotic Cell
• Example: skin cell
Skin cell
A skin cell will divide to form
two skin cells. The genetic
information must be the
same.
• Before a cell can divide, its genetic
information must be organized and it must
be doubled.
Organizing Genetic Material
1. DNA
2. Chromatin – DNA wrapped around
histone proteins (help maintain the shape
of chromosome and aid in the tight
packing of DNA)
3. Continues coiling
4. Chromosome – 2 molecules of DNA
Understanding Chromosomes
• FYI:
– Chromosomes only exist during cell division
– The DNA has doubled by replicating itself
How Are Chromosomes
Categorized?
• Sex chromosomes – c`somes that
determine the sex of an organism. For
example in humans X female Y Male.
Normal females have two X c`somes and
normal males have an X and a Y c`some.
• Autosomes – all the other c`somes. For
example in humans 44 c`somes are
autosomes and 2 are sex c`somes. Total
of 46 c`somes.
Homologous Chromosomes
• Homologous chromosome – two copies of
each autosome produced by sexual
reproduction
– Same size, same shape
• For example, if one c`some in a pair of
homologous c`somes contains a gene for
eye color so will the other c`some in the
homologous pair.
Karyotype
• Karyotype – a
photomicrograph of
the c`somes in a
dividing cell found in a
normal human.
– Used to examine an
individuals c`somes.
– Made by sampling a
person’s blood.
– White blood cells from
the sample are treated
with chemicals to
stimulate mitosis.
Diploid and Haploid Cells
• Diploid – cells having two sets of c`somes. Have both
autosomes (homologous c`somes) and sex c`somes.
– All normal human cells, except reproductive cells (sperm and
egg cells) are diploid cells.
– Abbreviated as 2n
• Haploid – human sperm and egg cells. Contain only one
set of c`somes. They have half the number of c`somes
that are present in diploid cells.
– Human haploid cells have only one c`some of each homologous
pair and only one sex c`some.
– Abbreviated as 1n
– When a sperm cell (1n) and an egg cell (1n) combine to create
the first cell of a new organism, the new cell will be diploid (2n).
Key Ideas Answered
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Question: Why do cells divide?
Answer: To maintain their volume to surface
ratio.
Question: How do cells divide?
Answer: 1. The cell organizes its genetic
information and doubles it.
a. Chromosomes are formed by DNA packing around histone
proteins
b. This period of the cell cycle is called Interphase where the:
– Cell grows, DNA replicates, and cell prepares to divide
Examining the Eukaryotic Cell
Cycle
• 90% of a cell’s life is spent in Interphase!
• Interphase
Divided into three phases:
G1 Phase – where cells function, cell grows in
size
S Phase – DNA is replicated
G2 Phase – where a cell can grow some more
before it divides
• A cell spends only 10% of it’s life dividing! Some
never divide!
• Onward to Cell Division!!!
Animal (Whitefish) Mitosis
Prophase
Metaphase
Anaphase
Telophase