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• What are the steps of the cell cycle?
Cellular Reproduction
The Cell Cycle, Mitosis, and Meiosis
Types of Cells
• Gametes: Sex Cells (Sperm & Eggs)
• Somatic Cells: all of the other cells in your
body
The Cell Cycle & Mitosis
• Somatic Cells divide into two genetically
identical cells via the cell cycle and mitosis
• The cell cycle is divided into three distinct
phases
– Interphase
– M Phase
– Cytokinesis
Mitosis
• My 2 Sis(ters)
– One cell becomes two sister cells
• Cells produced are diploid (2n)
• Daughter cells are identical to parent cell
– Same number of chromosomes in each (2n)
Diploid
• Asexual reproduction makes cells with the
same amount of DNA as the parent (Diploid)
– How many chromosomes will the offspring of
bacteria have if the parent has 6 chromosomes?
Interphase: Longest Phase
• G1 Phase: cell grows and new proteins are
made as cell prepares for DNA synthesis
• S phase: DNA replicates in the nucleus to form
sets of identical chromosomes
• G2 phase: Cell continues to grow and prepare
for mitosis. More proteins are made and
translocated.
M-Phase: Nucleus Divides
• Mitosis=karyokinesis (nucleus divides)
• Occurs in 4 stages
– Prophase: Tighten Up
– Metaphase: Line Up
– Anaphase: Separate
– Telophase: Relax
Prophase
• Chromatin condenses into chromosomes
• Nuclear envelop and nucleolus disappears
• Mitotic spindle forms
Metaphase & Anaphase
• Metaphase
– Chromosomes align on the equatorial plate
• Anaphase
– Sister chromatids separate and become individual
chromosomes
– Chromosomes move to opposite poles of the
spindle
Telophase
• Two nuclei visible
• Chromatin relaxes back into original size
Cytokinesis: Cytoplasm divides
• Animals
– Cleavage Furrow forms
– Cell separates into two cells and interphase begins
• Plants
– Cell plate forms midway between the two nuclei
– Cell membrane forms around each new cell
– Cell wall forms on each side of the cell plate
Meiosis
Gamete Production
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Meiosis
Similar in many ways to mitosis
Several differences however
Involves 2 cell divisions
Results in 4 cells with 1/2 the
normal genetic information.
Vocabulary:
Diploid (2N) - Normal amount of
genetic material
Haploid (N) - 1/2 the genetic
material.
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Meiosis
 Meiosis results in the formation of
haploid cells.
In Humans, these are the Ova (egg)
and sperm.
Ova are produced in the ovaries in
females
Process is called oogenesis
Sperm are produced in the testes
of males.
Process is called spermatogenesis
 Meiosis occurs in 2 phases: Meiosis I
& Meiosis II
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Steps of Meiosis
• Meiosis I: homologous chromosomes separate
• Meiosis II: sister chromatids separate
Meiosis I
 Prior to division, (S phase of
interphase), the amount of DNA doubles
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Homologous Chromosomes
• You receive one chromosome from your mom
(egg) and one from your dad (sperm)
• 23 pairs of chromosomes=46 total
Prophase I
 Chromatin shortens
and thickens into
chromosomes
 Homologous
chromosomes pair
with each other to
form tetrads (4
chromatids)
 Genes are
exchanged at
CHIASMATA
connections through
crossing over
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Crossing Over
 Segments of
homologous
chromosomes break
and reattach at
similar locations.
 Results in new
genetic combinations
of offspring.
 This is the main
advantage of sexual
reproduction
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Metaphase I
• HOMOLOGOUS
CHROMOSOMES
line up along the
equatorial plate
Anaphase I
 During Anaphase I, each
HOMOLOGOUS
CHROMOSOME is pulled to
opposite sides of the cell.
 Unlike mitosis, the
CENTROMERES DO NOT
BREAK.
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Telophase I
• A new nuclear
membrane starts
to form around
the cluster of
chromosomes at
each pole
• Sister
Chromatids are
no longer
identical due to
crossing over.
Meiosis II
 Begins after a short interphase but
DNA DOES NOT double
 Chromosomes randomly line-up along
metaphase plate like regular mitosis.
 During Anaphase II,
CENTROMERES BREAK and each
SISTER CHROMATID is pulled to
opposite sides of the cell.
 Nuclei reform and cytokinesis
usually occurs (although it is often
unequal).
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Sister chromatids
Gametes
• New sex cells are formed by Meiosis
– Sex cells made ME
Gametes
• Sex cells are haploid
– They have half as much DNA as the parent
• Humans have 46 chromosomes in their
somatic (body cells)
– How many are in your sperm and eggs?
Spermatogenesis & Oogenesis
Sperm
formation
Egg
formation
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Overview of Meiosis
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Meiosis vs. Mitosis
• Meiosis
–
–
–
–
Sexual Reproduction
4 sex cells
Haploid
Genetic Variation
• Mitosis
–
–
–
–
Asexual Reproduction
2 somatic cells
Diploid
Identical cells to parent
Fertilization
• To make a baby a sperm and egg cell must
unite together
– How many chromosomes will the baby have after
fertilization?
DNA and RNA
• DNA and RNA are nucleic acids composed of a
pentose, phosphate, and nitrogenous base.
• What are the differences?
What Time is It?
•
•
•
•
•
DR Pepper Time
DNA is transcribed to
RNA is translated to
Protein is expressed as
Traits
Genetic Disorders Caused by
Nondisjunction during Meiosis
• Down Syndrome
Klinefelter’s Syndrome
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