Cell Reproduction

1
Cell Reproduction
2
Chromosome Structure

• _DNA_ is a long, thin molecule that stores the
  information needed to direct the activities of
  cells.
• Genes are pieces of DNA that code information for
  particular activities. Genes are transmitted
  from parent cell to daughter cells.
• When a cell begins to divide, its DNA and
  associated proteins coil together into thick
  rod-shaped structures called _chromosomes_.
• Your chromosomes are about 60_ DNA and40
  protein.

• During interphase, before cell division begins,
  the chromosomes double. The two copies of each
  chromosome are called _chromatids, and are held
  together by a protein disk called a centromere.
• Humans have 23_ sets of two chromosomes in each
  of their body (somatic) cells. _Gametes_ (egg and
  sperm) have only one of each of the 23 different
  kinds of chromosomes.
• Each set of two chromosomes is called a
  homologous pair. Homologous chromosomes are
  similar in shape and size, and contain genes for
  the same_ traits.

Chromatid Chromatid
Two chromatids of a doubled chromosome
Centromere
3
Chromosomes Affect Development

• Each human chromosome holds __________________ of
  genes. _________ of these genes must be present
  to form a complete human.
• Extra or missing chromosomes cause severe
  problems. ____________________, an extra
  chromosome 21, causes Down syndrome.
• ________________________, either by amniocentesis
  or by chorionic villi sampling, can determine if
  a baby has Down syndrome or other chromosomal
  abnormalities.
• Although rare, other changes can happen to the
  genes in chromosomes. These changes are called
  ___________________.

• Pieces of chromosomes can be missing
  (________________) or copied (____________________
  ). Chromosome fragments can also rejoin the
  chromosome backwards (_________________) or join
  a non-homologous chromosome (_____________________
  ).
• Chromosomes determine your sex. If you have two
  X chromosomes, youre ______________, but an X
  and a Y make you a __________.

4
Mitosis and Cell Division

• When bacteria reproduce, they simply split in
  half. This process is called _binary fission_.
• During binary fission, the bacterium copies its
  _DNA_, forms a new cell membrane and a new cell
  wall. Afterwards, the cell splits in two.

• Eukaryotic cells undergo nuclear division, called
  mitosis_.
• The life cycle of eukaryotic cells is a repeating
  series of steps called the cell
  cycle_____________.

G1 Phase - cell growth The cell carries out its
normal activities. This is most of the time
between cell divisions.
Cyto- kinesis
Interphase
Mitosis
G2 Phase - more growth and preparation for mitosis
S Phase - DNA is copied. Chromosomes exist as
chromatids.

5
What Happens In Mitosis?

• ________________ cells spend most of their lives
  in the G1, S, and G2 phases, which together are
  called___________________.
• At the end of interphase, the cell begins to
  build the structures needed to move chromosomes
  to opposite ends of the cell.
• In animal cells, a pair of organelles called
  __________________ move to opposite ends of the
  cell.
• As the centrioles separate, protein strands
  called ____________________ form between them.
  Other spindle fibers extend outwards from
  centromeres binding the______________________
  together.

• When the spindle fibers are complete, each
  chromatid is attached to _________________ poles
  of the cell.
• Next, the ________________ holding together the
  chromatids separate, and the _____________________
  ______, pulling the chromatids apart, and toward
  the poles of the cell. Each pole of the cell will
  receive a complete set of chromosomes.
• The last step of cell division is formation of
  two new __________________________ around the two
  sets of chromosomes, and a pinching inwards of
  the cell membrane to split the cell in half,
  called ________________________.

6
Stages of Mitosis

• Anaphase - Chromatids separate while centromeres
  divide, separated chromatids move towards
  opposite poles of the cell

• Prophase - Doubled chromosomes become visible,
  nuclear envelope disappears, spindle fibers begin
  to appear.

• Metaphase - Chromosomes move to the center of
  the cell and are aligned along the cells
  equator.

• Telophase - Chromosomes uncoil and nuclear
  envelopes form while spindle fibers disappear.
  Mitosis is complete. Cytokinesis now begins.

7
What Happens in Meiosis?

• In organisms that reproduce sexually, the sex
  cells (_______________) fuse together to produce
  the offspring or _____________. Gametes must have
  ________ of each type of chromosome, not two.
• In the sex organs of animals, gametes are
  produced by ____________, which is also called
  reduction division.
• In plants, meiosis is usually used to produce
  _________________.
• Meiosis consists of ________ successive nuclear
  divisions, but the DNA is only copied in ________
  of them. Thus, one diploid cell produces four
  haploid cells.

• During meiosis, ______________________ can
  happen. This is when the arms of paired
  chromosomes cross over each other and pieces of
  the chromosomes break off, then reattach to the
  wrong chromosome in the pair. The result of
  cross-over is ____________________________________
  _____________________.

Meiosis I
Meiosis II

8
Meiosis I

• The two nuclear divisions of meiosis are divided
  into eight stages. Although they have the same
  names as the stages of mitosis, what happens in
  meiosis is different.

• Prophase I - Chromosomes condense and nuclear
  envelope breaks down, just like in mitosis. But
  homologous chromosomes also pair up and crossover
  can occur!

• Anaphase I - The homologues separate and are
  pulled by spindle fibers to opposite poles,
  however, chromatids do not separate. Each
  chromosome still consists of two joined
  chromatids. Nondisjunction can occur!.

• Metaphase I - Pairs of homologous chromosomes
  (called tetrads) are moved by spindle fibers to
  the cells equator.

• Telophase I - Individual chromosomes gather at
  each pole, and in most organisms, the cytoplasm
  divides. Daughter cells are haploid!

9
Meiosis II

• Prophase II - As in mitosis Chromosomes
  condense, nuclear envelope disappears, and
  spindle apparatus appears. Chromosomes do not
  double in meiosis II! Each of two dividing
  daughter cells from meiosis I is haploid.

• Anaphase II - Centromeres divide, and chromatids
  (now called chromosomes) move towards opposite
  poles of the cell.

• Telophase II - Chromosomes uncoil at cells
  poles. Nuclear membranes and organelles
  reappear. Spindle apparatus disappears. The
  four daughter cells produced are haploid.

• Metaphase II - Chromosomes are at the cells
  equator.