Download Characteristic #4

Characteristic #4
All living things reproduce using the
same genetic mechanism (code)
• Each organism reproduces its own species
• Offspring inherit genetic instructions from their
parents through a molecule called DNA
• Offspring can differ from their parents (genetic
variation)
Mitosis & Meiosis
Making New Cells from Old Cells
Passing on Information
 Genetics is the study of the transfer of
information at the level of the cell.
• DNA stores genetic information
• DNA is divided into chromosomes
• Chromosomes come in homologous pairs
• Genes control traits
• Genes are on chromosomes
• Chromosomes
(DNA) are in the
cell nucleus
• Humans have 23
pairs of
chromosomes
• The number of
chromosome pairs
varies in each
species
Chromosomes
New Terminology
• Diploid: a cell with chromosome pairs.
Human diploid cells have 23 pairs (46
chromosomes).
• Somatic Cells: body cells. All somatic
cells are diploid
New Terminology
• Haploid: a cell that does not have pairs of
chromosomes. Human haploid cells have
23 chromosomes.
• Gamete: sex cell (sperm, egg). All
gametes are haploid.
Mitosis & the Cell Cycle
• Function: growth, repair,
and replacement of cells.
• A diploid parent cell
replicates its DNA, then splits in half.
• Both new daughter cells have a complete
set of DNA
• Mitosis creates autosomes (body cells)
Three Stages of the Cell Cycle
The cell cycle has 3 stages:
• Interphase: growth and
replication
• Mitosis: the nucleus divides
• Cytokinesis: the cell divides
Interphase
The cell grows and the DNA replicates
Interphase
At the beginning of interphase, the DNA is
relaxed (chromatin). At the end, it tightens
up (chromosomes)
Interphase
After the chromosome (chromatid) makes a
copy of itself, the new copy sticks to the old
one to form an “X” shape (sister chromatids)
Before Replication
After Replication
Terminology
• Spindle fibers –
strand-like fibers
in the cell
• Centrioles –
animal cell
organelles that
produce spindle
fibers
Mitosis
The cytoplasm of the cell divides, ending with a
complete set of DNA on each side of the cell.
Four steps:
– Prophase
– Metaphase
– Anaphase
– Telophase
Prophase
Nucleus dissolves, spindle fibers stretch
across the cell, centrioles move to poles
Metaphase
The chromosomes line up on the cell equator,
fibers attach to them from both sides
Anaphase
The fibers shorten, splitting the chromosomes &
pulling half of each pair to opposite poles
Telophase
A new nucleus forms around each set of
chromosomes, the cell starts to split in half
the cell splits into
two identical new
daughter cells
Cytokinesis
Cytokinesis
Animal cells: a cleavage furrow forms & the cell splits
• Plant cells: a cell plate grows across the center of the
cell
Summary
• Mitosis is a way for cells to pass
information to new somatic cells within the
same organism
• The cell cycle & mitosis result in two
diploid daughter cells that are identical to
the original diploid parent cell
• Cell cycle and Mitosis are important in
growth, replacement, and repair of all body
cells
Meiosis
Homologous Chromosomes
Chromosomes pair with the same genes
Humans have 23 pairs of
homologous chromosomes
Sexual Reproduction
• Male sperm fertilizes the female egg
• DNA from 2 parents is combined
• To produce a baby with a normal # of
chromosomes, each sperm and egg must
have half the number of chromosomes
Gametes:
Sex Cells
Sperm and Eggs
• Found only in the
testicles & ovaries
• Gametes are haploid:
they have 23
chromosomes (no pairs)
• Formed through meiosis
Differences between gametes and body cells
Gametes
•
•
•
•
•
Sex cells (sperm, eggs)
Testicles and ovaries
Haploid
Made through meiosis
No homologous pairs
Autosomes
•
•
•
•
•
Body cells
Everywhere else
Diploid
Made through mitosis
Homologous pairs
Meiosis produces four different haploid daughter
cells from one diploid parent cell
Original diploid
parent cell
4 haploid
daughter cells
How does Meiosis Work?
• DNA replicates in the parent cell
• Homologous chromosomes swap genetic
information by “Crossing over”
• The parent cell divides in half – each new
cell now has one complete copy of DNA
• These 2 new cells divide again, splitting
their copy of DNA in half
• 4 new haploid daughter cells have only ½
the DNA of the parent
A look at Meiosis
Crossing Over
• Homologous chromosomes move very close
together… sometimes they swap pieces.
• This creates brand new combinations of genes on
each chromosome
• Crossing over leads to genetic variation – the
offspring has different traits than either parent
Comparing Mitosis and Meiosis
• Mitosis: diploid parent produces 2 identical
diploid daughters
• Meiosis: diploid parent produces 4 unique
haploid daughters
After Meiosis
The 4 daughter cells will
have half as many
chromosomes as the
parent.
After Mitosis
The 2 daughter cells will
have the same number
of chromosomes as the
parent.
Meiosis vs. Mitosis
• If the parent cell has 60 chromosomes, how
many will the daughter have after meiosis?
• Daughter cells produced by mitosis have 16
chromosomes. How many did the parent cell
have?
• A sperm has 15 chromosomes. How many
chromosomes did the parent cell have?
• If a daughter cell has 10 chromosomes and
the parent had 20, was the daughter cell
made through meiosis or mitosis?
Other Reproductive Issues
Grab Bag of Knowledge
•
•
•
•
•
Selective Breeding
Asexual reproduction
Alternation of generations
Incomplete metamorphosis
Complete metamorphosis
Selective
Breeding
Dairy cows have been modified through selective
breeding for large udders and high milk production. As a
result, many cows have udders so large that they cannot
walk without swinging their legs out to the side.
Asexual Reproduction
Asexual reproduction is when one parent
produces one or more identical offspring
Examples of Asexual Reproduction
• A branch of a tree
grows into a new tree
when planted
• Hydra create offspring
that grow from their
body and then pinch off
Sexual Reproduction
Sexual reproduction involves the
fertilization of an egg by a sperm (two
parents). Offspring are different from the
parents.
Animal Life Cycles:
Metamorphosis
• Some organisms go through changes in
form as they grow
• Insects undergo metamorphosis
• Incomplete metamorphosis has 3 stages:
egg, nymph, adult
• Complete metamorphosis has 4 stages:
egg, larvae, pupae, adult
Incomplete Metamorphosis
Three stages:
• Egg
• Nymph: similar to adult but can’t reproduce
• Adult
Incomplete
Metamorphosis
in
Grasshoppers
Eggs
Nymph
Adult
Complete Metamorphosis
Four stages:
•
•
•
•
Egg
Larvae (caterpillar)
Pupae (cocoon)
Adult
Butterfly Development
Development of the crow butterfly: (Above left)
egg; (Left) larvae; Above: pupae and
cocoon; next slide: adult
Plant Life Cycles
Alternation of Generations
Plants alternate
between a
diploid and
haploid phase.
This is the
alternation of
generations.
What kind of reproduction is shown
here?
What kind of reproduction is shown
here?
What kind of reproduction is shown
here?
What kind of reproduction is shown
here?
What kind of reproduction is shown
here?
What kind of reproduction is shown
here?
What kind of reproduction is shown
here?
What kind of reproduction is shown
here?
What kind of reproduction is shown
here?