Transcript Genetics Part 2

Eukaryotic Cell Cycle
• Cell cycle: repeating sequence of cellular
growth and division during the life of the cell
– Interphase
– Mitosis
– Cytokinesis
Interphase
• Cell is growing and
preparing to divide
• G1 (First Gap) phase
– Cell grows rapidly
• S (synthesis) phase
– Cell’s DNA is copied
– Each chromosome now has
2 identical chromatids
• G2 (Second Gap) phase
– Cell continues to grow and
prepare for division
– Microtubules form
Mitosis
• Process of dividing the nucleus into two
daughter nuclei
– Prophase
– Metaphase
– Anaphase
– Telophase
Prophase
• Chromosomes
condense
• Nuclear membrane
dissolves
• Centrosomes
(centrioles) move to
opposite poles and
spindle forms
Metaphase
• Condensed
chromosomes line up at
cell’s equator
• Spindle fibers link the
individual chromatids to
opposite poles
Anaphase
• Spindle fibers shorten
• Chromatids pulled to
opposite poles of cell
giving each pole
identical sets of
chromosomes
Telophase
• New nuclear envelope
forms at each pole
• Spindle dissolves
• Chromosomes uncoil
(chromatin)
Cytokinesis
• Cell membrane grows
into the center of the
cell and divides it into
two daughter cells of
equal size
– each daughter cell has
about half of the
parent’s cytoplasm and
organelles
Cytokinesis
• Animal cells: cell is pinched in half by a belt of protein threads
• Plant cells: vesicles holding cell wall material line up in the middle to fuse
into a cell plate which separates the new cells
End Results
• Two identical cells
• New daughter cells half
the size of the parent
cell
• Each cell enters G1
Types of Cell Reproduction
• Asexual: single parent
passes a complete copy
of its genetic
information to each of
its offspring
– Offspring look identical
to parent (MITOSIS)
Types of Cell Reproduction
• Sexual: two parents give
genetic material to
produce offspring that
are genetically different
from their parents
(MEIOSIS)
What are some advantages of
sexual reproduction?
Meiosis
• Process in which a cell is
divided and produces
gametes (sperm or
eggs): 2 rounds of
division (P-I, M-I, A-I, TI, then P-II, M-II, A-II,
and T-II)
– end with 4 haploid cells
Homologous Chromosomes
• Chromosomes that are
similar in size, shape, and in
kinds of genes that they
contain
• Each chromosome in a
homologous pair comes
from one of the two parents
• Each species has a different
number
Chromosome Number
• Gametes are haploid
• Somatic cells are diploid
Example:
 Horse skin cell = 64
chromosomes = diploid
(2n)
 Horse egg cell = 32
chromosomes = haploid
(n)
Chromosome Number
• Species: a population of
organisms that are able
to breed and produce
fertile offspring
– Same number of
chromosomes
Crossing Over
• Prophase I
• Chromatids exchange
genetic material
between homologous
chromosomes during
meiosis
 What is the advantage
of crossing over?
Meiosis
Two divisions to get 4 haploid cells
Comparing Mitosis and Meiosis
Comparing Mitosis and Meiosis
Process
Location
# of Cells
Produced
Haploid/
Diploid
Type of Cell
Produced
Importance of
Process
Mitosis
Somatic Cells
(Ex: skin cells)
2
diploid
Identical
diploid cells
Healing/repair,
maintenance/replac
ement of old cells,
and growth
Meiosis
Sex Cells
(gametes)
4
haploid
Different
haploid cells
Reproductive
purposes; increases
genetic diversity
amongst organisms