2. ---Cell division is the process in which the
genetic information of a cell is passed along
to the next generation of cells.
Involves the division of a parent cell into 2
daughter cells.
3. Characteristics of cell division
Replication of DNA
Equal distribution of DNA to opposite
ends of the dividing cell
Separation into two daughter cells
7. >>>Cell division consists of nuclear division
and cytoplasmic division.
---Mitosis is the division of the nucleus.
-During this process the DNA is equally
distributed into 2 daughter nuclei.
8. -The division of the nucleus is usually
followed quickly by cytokinesis
---Cytokinesis is the division of the
cytoplasm that forms 2 separate daughter
cells, each containing a single nucleus.
9. chromatin
proteins
DNA
During the cell cycle
the chromosomes
replicate.
---Chromosomes are
threadlike structures
composed of
chromatin, which is
DNA
and proteins bound to
it.
13. DNA Replication
• After the DNA has replicated, there are now 2
chromosomes that are attached at the
centromere.
• These 2 chromosomes are called sister
chromatids.
• So, DNA replication produces a replicated
chromosome with 2 identical sister
chromatids.
16. Sister Chromatids
• During mitosis (cell division), the 2 sister
chromatids separate, and each
chromatid forms an individual
chromosome.
• These 2 chromosomes get split
between the 2 daughter cells resulting
from a mitotic division.
17. -If the chromosomes are photographed, the
pairs can be arranged by size, shape and
staining pattern to produce a karyotype
18. ---Homologous chromosomes (homologues) are a pair of
chromosomes that contain the same genes. They have
the same size, centromere position and staining pattern.
These are not the same as replicated chromosomes. For
each pair of homologous chromosomes, you received
one chromosome from your mother and one from your
father.
19. ---Diploid is the condition where cells have
pairs of homologous chromosomes
20. In the ordinary body cells (not sperm or eggs) of
many organisms the chromosomes occur in
pairs.
-Each species has a characteristic number of
chromosomes and the individual
chromosomes are distinguished by size,
shape, and staining pattern
-Human cells contain 46 chromosomes, 23
pairs of homologous chromosomes.
21. Humans: Autosomes (22 pairs) + 1 pair of sex
chromosomes
---Autosomes are the non-sex chromosomes.
22. Some cells have only half of the set of
chromosomes and are called haploid.
---Haploid is the condition in which cells
contain one set of chromosomes.
No pairs.
-the haploid condition is found only in
the gametes.
23. ---Gametes are haploid egg or sperm cells and
contain half the number of chromosomes of
ordinary cells.
Two haploid gametes unite during fertilization to
form a zygote (a fertilized egg).
---Zygote is a diploid cell that results from the
union of two haploid gametes.
24. MITOSIS (a.k.a. M-phase)- Nuclear Division
The duplicated chromosomes are
organized on a network of microtubules -
and separated
The mitotic phase (M-phase) of the cell
cycle is divided into five phases
EARLY PROPHASE, LATE PROPHASE,
METAPHASE, ANAPHASE AND
TELOPHASE
25. Spindle Apparatus
• This is part of the cytoskeleton in eukaryotic
cells.
• It separates the chromosomes into the
daughter cells during cell division.
• Remember, during S-phase, prior to cell
division, the chromosomes duplicate. So
each duplicated chromosome consists of a
pair of sister chromatids.
26. Mitosis – Early Prophase
-chromatin condenses
-spindle apparatus forms
MITOSIS
spindle
formation
condensing
chromosomes
PROPHASE
27. Kinetochores
• These are protein structures on
chromosomes where spindle fibers
attach during mitosis.
• Think of these as handles on the
chromosomes that the spindle fibers
hold onto.
33. By the end of telophase replication of the
nucleus is complete and two genetically
identical daughter nuclei are present.
34. Cell divides in two; each
daughter cell receives
one
nucleus and about half of
the cytoplasm.
CYTOKINESIS
35. ASEXUAL
REPRODUCTION
SEXUAL
REPRODUCTION
Only one parent Two parents give rise
to offspring
Single parent passes
on all its genes
Each parent passes on
half its genes
Rare genetic
differences in
offspring are the result
of DNA changes, or
mutations
Greater genetic
variation with offspring
being genetically
different from their
parents and siblings
36. Meiosis
• Meiosis is a pre-requisite for sexual reproduction.
• Occurs in the ovaries and the testes in mammals.
• A meiotic division followed by 2 rounds of
cytokinesis to produce 4 daughter cells that
become gametes (sperm or egg).
• Gametes carry HALF the genetic material of the
parent. So the cells produced by meiosis are not
identical to the parent cell.
37. >>>>>>Meiosis reduces chromosome
number from diploid to haploid
-Chromosomes replication precedes
meiosis (just like mitosis).
In meiosis, each daughter cell receives
one member of each pair of homologous
chromosomes.
40. Meiosis II
• A second division, called Meiosis II
separates the sister chromatids and
puts one chromatid into each daughter
nuclei.
• So, at the end of meiosis, there are 4
haploid daughter nuclei, each with one
copy of each homologous chromosome.
42. Homologous chromosomes undergo pairing up
Sister chromatids are linked at centromeres,
non-sister chromatids are linked at chiasmata
Genetic crossing over occurs, exchange of
genetic info between un-identical
chromosomes.
Unique events occur during meiosis I
47. MEIOSIS I
Prophase I
-nuclear envelope
disappears
paired homologous
chromosomes
spindle
microtubule
chiasmata
MEIOSIS I
48. MEIOSIS I
Metaphase I
-chromosome pairs
align at the equator,
called the
metaphase plate
-kinetochores of
sister chromatids
face same pole
-centromeres of
homologues face
opposite poles.
MEIOSIS I
recombined
chromosomes
49. MEIOSIS I
Anaphase I
-spindle microtubules
interact with kinetochore
fibers
-homologous chromosomes
move toward opposite poles
-sister chromatids remain
attached (this is different
than mitosis)
MEIOSIS I
50. MEIOSIS I
Telophase I and
cytokinesis
-chromosomes arrive at poles
-cell divides
MEIOSIS I
