Reproduction
DNA in the Nucleus
Chromatin ~ DNA
coated in protective
proteins.
Chromosome ~
Chromatin that has
been copied and
coiled up into an X
shape to prepare for
cell division.
Parts of a chromosome:
•Histones
•Centromere
•Sister Chromatids
Sister Chromatids
 Two complete copies
of DNA joined at the
centromere.
 Copy is made by
replication.
 Homologues ~ Each
sister chromatid
contains the same
genetic information.
Diploid ~ Describes a cell that has
two of each kind of chromosome
(homologous pairs). Normal body
cells are diploid. 2n
Humans 2n = 46
Haploid ~ A cell that has one of
each kind of chromosome.
Gametes (sex cells) are haploid. N
Humans n = 23
Homologous pairs ~
Chromosomes occur in
pairs. Both chromosomes
will carry similar
information. One came from
the father, the other came
from the mother.
Types of Reproduction




Asexual
Produces somatic cells
(body cells)
Produces diploid cells
Makes clones
Cells are made by




Sexual
Produces gametes (sex
cells)
Produces haploid cells
Makes offspring that are
genetically different from
the parents.
Cells are made by
Asexual Reproduction ~
Reproduction that does
not require the exchange
of DNA. There is only one
parent, and the offspring
will be clones (have the
same DNA) of the parent.
1. Fragmentation
2. Budding
3. Spores
Mitosis Terms
Parent cell
Spindle
Daughter cell
The Cell Life
Cycle:
1. Interphase
2. Mitosis
• Prophase
•
Metaphase
• Anaphase
• Telophase
Onion cells in
interphase
3. Cytokinesis
Interphase: The “living” stage.
Interphase: A cell is
carrying out normal
functions for homeostasis.
At the end, replication of
DNA occurs, and the cell is
called a “Mother” cell.
Onion cells in
interphase.
Prophase: The 1st phase of Mitosis
Prophase:
•Nuclear Membrane
Dissolves
•Chromatin coils up into
chromosomes
•Centrioles move to
opposite sides of
cell and form spindle
Onion Cell in Prophase:
Note that the nuclear
material is spreading
out, due to the
dissolution of the
nuclear membrane.
Metaphase: 2nd Phase of Mitosis
Metaphase:
Chromosomes line up
on center of spindle.
Onion cell in metaphase:
The chromosomes are
gathered in the middle
Anaphase: 3rd Stage in Mitosis
Anaphase: The
chromosomes split into
separate sister
chromatids, and move
to opposite centrioles
Onion Cell in anaphase:
Each chromatid is
dragged to opposite
sides.
Telophase: Last stage of Mitosis
Telophase:
•Two new nuclear membranes
form.
• Spindle dissolves.
• Chromatids uncoil into
chromatin.
Onion Cell in telophase:
The chromosomes are in 2
separate nuclei in the
same cell.
Cytokinesis: Cell splits into two
daughter cells.
Daughter cells of onion
Cytokinesis (fission):
After two nuclei have
formed, the mother cell
divides to form 2
daughter cells.
Fish cells undergoing
cytokinesis
Differences in Plant and Animal Cell
Mitosis
Plant Cells
Animal Cells
 No centrioles
 Centrioles form
spindle
 Formation of cell plate
in telophase
 Cleavage furrow
develops in telophase
Sexual Reproduction ~
Reproduction that
requires the exchange of
DNA between two
members of the same
species. The offspring
will have DNA that
combines genes from
both parents, but will be
unique to the offspring.
1. Haploid
2. Gametes
3. Sperm
4. Ovum
Meiosis
 Two divisions, no replication of DNA in between.
 Chromosomes will exchange pieces to ensure
genetic diversity of offspring.
 Resulting cells will be haploid gametes.
Meiosis ~ Process by which haploid cells are
produced.
Spermatogenesis ~ Meiosis that produces
four new sperm cells from one mother cell.
Oogenesis ~ Meiosis that produces one new
ovum from one mother cell.
Meiosis I
 Prophase I ~ Same events as in prophase of
mitosis, except:
Crossing over ~ Pairs exchange pieces with each
other.
Chiasmata ~ Sites on chromosomes where crossing
over occurs.
 Metaphase I ~ Homologous pairs line up on
metaphase plate. Centromeres of each are
attached to separate centrioles.
 Anaphase I/Telophase I ~ Pairs separate, and
intact chromosomes are pulled to opposite
poles. Spindle dissolves, new nuclear
membranes form. Cell divides.
Meiosis II
 Prophase II ~ (No DNA duplication has
occurred!) New spindle forms, nuclear
membrane dissolves.
 Metaphase II ~ Chromosomes line up.
 Anaphase II ~ Centromeres break, daughter
chromosomes move to opposite sides.
 Telophase II ~ Same as mitosis. Cells are
haploid.
Spermatogenesis ~ 4 viable daughter cells.
Oogenesis ~ 3 commit apoptosis, only one continues.
Cell Development
 Fertilization
 Zygote
 Embryo
 Cell differentiation ~
Process in which a
developing cell is
specialized. Genes are
selectively “turned off” to
determine the cell type.