9th Grade Cell Biology Cell Cycle
9th Grade Cell Biology Cell Cycle
Cell Biology: Cell Cycle/Genetics
Notes – Unit 5 – Biology
• Reproduction at the cellular level occurs when one cell called the
• Mother Cell divides and forms new cells called the
• Daughter Cells
• Unicellular organisms which consist of
• 1 cell, do what by cellular division?
• Binary Fission
• Multi-cellular organisms which consist of
• 2 or more cells, do what by cellular division?
• Why must cellular division occur?
• So organisms can reproduce, repair, and grow
• What do daughter cells receive from the parent cell?
The same DNA
• Human bodies rely on cell division to:
• 1. Reproduce
• 2. Repair
• 3. Grow
• Bacteria divide every 20 minutes. A human
cell divides every
• 20 hours.
• The production of offspring from one parent is
• Asexual Reproduction
• Offspring produced from the union of two
special parental cells is
• Sexual Reproduction
• Asexual Reproduction
• Binary Fission
• Prokaryotes, Bacteria
• Other methods of asexual reproduction
• 1. Vegetative Propagation (strawberries)
• 2. Regeneration (sea stars)
• 3. Budding (Yeast)
IV. The Cell Cycle
A. The series of changes a cell undergoes from the
time it is formed until it reproduces
B. The cell cycle consists of
• Sexual Reproduction
• Sexual reproduction results from the joining of
specialized sex cells called
• The male gamete is called the
• The female gamete is called the
• ovum or egg.
• In the process of fertilization, the egg and sperm
combine to form the zygote.
• Cell division of eukaryotic cells involves…
• As a result of mitosis, each daughter cell receives an exact copy of the
chromosomes present in the parent cell (the directions).
• Each kind of eukaryotic organism has a specific number of chromosomes in its
body cells. Body cells are called
• Somatic cells.
• Humans have 46 chromosomes. Goldfish have 94. Corn plants have 20.
Mosquitos have 6!
• Cell replication has three main parts… it is called the Cell Cycle
DNA Divides (Mitosis)
Cell Divides (CYTOKINESIS)
• Although the whole cycle may take up to 20 hours, the actual
chromosome division is less than 1 hour. The time between divisions is
• What happens during interphase?
Duplicating Cell Material
Cell Grows to nearly double its size
• The hereditary material (DNA and Protein) is called
• chromatin (tin is very thin)
• At the start of the mitosis the chromatin begins to coil up and condense
forming short thick rods called
• Each one has two strands called sister chromatids (tids are a
chromosomes kids), held together at the centromere (centromere is at
Diagram of Interphase:
Phases of Mitosis
• What happens in prophase?
• 1. nuclear membrane disassembled
• 2. nucleolus seems to disappear
• 3. chromatin is packaged as (becomes) chromosomes
• 4. spindle apparatus (only fibers in plants) begins to
• Protein tubes called spindle fibers form
between the centrioles. These with additional
tubules form the aster.
• The function of the aster is unknown. Many
plant cells have spindle fibers but not
centrioles and asters.
• What happens in metaphase (middlephase!)?
• 1. Chromosomes attach to the spindle fibers
(apparatus in animals)
• 2. Chromosome align along equator (middle)
• This is the best place to study chromosomes.
• Chromosomes are visible and lined up in the
• What happens in anaphase?
• 1. Centromeres separate (sister chromatids
become 2 chromosomes!)
• 2. Microtubules (spindle fibers) shorten
• 3. Chromosomes are pulled towards the poles
• What happens in telophase?
• 1. Chromosomes reach poles
• 2. Nuclear membrane reforms
• 3. Nucleolus reappears
• 4. Chromosomes de-condense
• Begins during …Telophase
• In animal cells the cell membrane pinches
inward and together. In plant cells a cell plate
must be formed first which is produced by the
Eukaryotic Cell Cycle -Stages
1. Interphase (3 parts) – cell spends most of time growing
and protein synthesis
2. G1 Phase – Growth 1 - Cell grows does “daily activities”
3. S Phase – Synthesis -DNA is copied
4. G2 Phase – Growth 2- Organelles are copied
5. M Phase – Mitosis - Chromosomes are separated into
the 2 ends of the cell, each pole will become a new cell
that is exactly the same as the old
6. C Phase – Cytokinesis – Cytoplasm divides and 2
identical daughter cells are formed
DNA constricts into chromosomes
Nuclear membrane disappears
Chromosomes align in the middle of the cell
Chromosomes are pulled apart to opposite sides
of the cell and form halves called
Telophase, the final stage of mitosis
Begins when chromosomes have completed
Nuclear membrane reforms
Chromosomes begin to unwind back into
Cytokinesis – begins when the
Cell membrane divides and a ring pinches the
two cells apart
• All cells produced through mitosis have the same
number of chromosomes as their parent cell.
• What would happen if two mitotic cells combined
in sexual reproduction?
• In humans this would result in a cell with 92
• It would no longer be human. It would be an
How many chromosomes would the daughter cells have?
Chromosomes in somatic cells occur in pairs called
Humans have 46 chromosomes with 23 pairs of
homologs. This is said to be diploid which means
there are 23 sets of homologous pairs (2n).
A gamete has only one member of each pair (half the
diploid number). A human gamete (egg and sperm)
has only 23 chromosomes and is said to be haploid
(n) “half loid”.
• Meiosis reduces the number of chromosomes
to half the number in somatic cells. This
process requires two successive cell divisions.
• Meiosis I (reduction division)
• Meiosis II
• Preceded by the synthesis of DNA and replication
of the chromosomes (Interphase?).
• Homologous chromosomes come together –
process is called
• Pairing Chromosomes
• Chromosomes lie next to each other forming a
• What happens?
Prophase I Crossing Over
Chromosomes Cross Over genetic
Chromosomes line up in middle of
Chromosomes are pulled
apart by spindle fibers
move to poles of cell:
• Meiosis I is the “reduction division”. It
reduces the number of chromosomes from
the diploid (2n) to the haploid (n) number.
• MEIOSIS II
• Meiosis II is similar to mitosis but is not
preceded by the replication of DNA (no
Chromosomes stay condensed:
But do not replicate again!!!
Haploid Chromosomes line up in
the middle of the cells
Anaphase II: Haploid Chromosomes are pulled apart
Telophase II: Four Nuclei are formed and four new
cells are created
• Each of the daughter cells produced in meiosis
II is haploid. Meiosis in male cells results in
four cells that differentiate or change into
gametes (sperm). Meiosis in female cells
results in only one viable egg cell as the
cytoplasm divides unequally.
Fundamentals of Genetics
• The passing of traits from parents to offspring is called
• The scientific study of heredity is called
Traits are transmitted by means of
Chromatin Network: (rod-shaped structures within the nucleus)
• Units of heredity are called
• Gregor Mendel July 22, 1822 (monk and teacher)
• Pea Plants
Mendel did experiments using
The Stamen and Pistol (gametes).
When peas fertilize themselves it is called
After many generations, offspring are genetically identical and
have the same traits.
Mendel cross-pollinated pea plants
Focused his work on 7 different traits
flower/seed coat color:
yellow vs. green
smooth vs. wrinkled
green vs. yellow
inflated vs. pinched
tall vs. short
axial vs. terminal
purple vs. white flowers
grey vs. white seed coats
Counted the offspring of each phenotype and analyzed the
Mendel crossed two pure breeding plants.
The parent plants were called the
Parental (P) generation.
He performed Cross Pollination in order to mix the genes.
The results and first generation was the 1st Filial Generation or F1 Generation
(Offspring of Parental Generation
After testing all of the traits, Mendel discovered that one trait in each pair showed
up in the F1 generation. The other trait seemed to disappear.
Next he allowed the F1 to self pollinate, producing the F2 generation.
Tall: Short = 3:1
How would you explain this?
The Principle of Dominance
• The principle of dominance states that one factor (gene) in a pair
may prevent the other factor (gene) in the pair from being
• A gene that masks the other gene in a pair is called
• The Dominant Gene.
• The gene that is hidden in the F1 generation is called
• The Recessive Gene.
• Geneticists use the following symbols:
• Dominant – Capital Letter
• Recessive – Lower case letter
• When the two genes are identical the individual is said to be
• When the two genes are both dominant it is
• Homozygous Dominant (Represented by two Capital Letters. BB)
• Individuals with a dominant gene and a recessive are
• Heterozygous (One Capital and one lower case letter. Bb)
• The Principle of Segregation
• The principle of segregation states that the members of each pair of genes
separate, or segregate, when gametes are formed.
• When does this happen?
• Anaphase II of Meiosis
• Draw this phase of the cell cycle.
Principle of Independent Assortment
• The principle in independent assortment states that two or
more pairs of genes segregate independently of one another
during the formation of gametes. However, these genes need
to be on different chromosomes. Mendel was lucky since the
traits he found in peas were on different chromosomes.
A term used to refer to either member of a pair of genes is
The pairs of alleles in the cells of an organism make up
A trait that is actually expressed in an organism’s appears is
The Punnett Square
• A grid, or chart which shows all the possible gene
combinations for a cross (male is traditionally across
the top and female is on the left side.
• Draw a punnett square of the following cross:
Male: Brown Eyes (BB) x Female Brown Eyes (Bb)
• Crosses involving one trait are called
• Monohybrid crosses.
• Crosses Involving Two Traits are called
• Dihybrid crosses.
• A cross involving two pairs of alleles is called a
• Dihybrid cross. (This is proof of Independent
• Not all phenotypes result from dominant and recessive genes
• Here both alleles are expressed.
Manx cat – homozygous for no tail (NN)
Normal Cat – homozygous for long tail (LL)
• Cross a normal with a Manx cat in a Punnet square and then
list the phenotypes and genotypes:
• Try this one:
Red Morning Glory (RR)
White Morning Glory (WW)
Cross a white and a red morning glory.
Curl Tongue and Mid-digital Hair
Pigment and Lobed Ears
1. New cells from mitosis develop into different
types of cells with specialized functions
• can divide to form two new stem cells
• can divide to form a stem cell and a progenitor cell
•totipotent – can give rise to any cell type
• pluripotent – can give rise to a restricted number of cell
• committed cell
• can divide to become any of a restricted number of cells
• What would be some uses for acquiring stem
• What are the controversies?
• Why not use progenitor cells?
• Where do you stand?