cell division unit chapter 10 section 2 chapter 11 section 4
TRANSCRIPT
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Cell Division Unit
Chapter 10 Section 2
Chapter 11 Section 4
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Process of Making a ChromosomeChromosome
Supercoils
Coils
Nucleosome
Histones
DNA
double
helix
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Chromatin – DNA tightly coiled around proteins called Histones
Nucleosome – beadlike structure made of chromatin
Supercoils – nucleosomes packed together
Chromosome – tightly packed supercoils
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Chromosomes Made of DNA and Histones (protein) Function :
- passes genetic info. from 1 generation to the next
Genes- located on chromosomes
- information about traits are located here
Traits – characteristics passed on by your parents
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Chromosomes Numbers Every organism has a specific # of
chromosomes
Humans = 46 chromosomes
The # of chromosomes DOES NOT indicate the COMPLEXITY of an organism
Example – a goldfish has 124 chromosomes
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Structure of Chromosomes
Chromosomes are replicated (copied) before cell division (when a new cells are
developed)
This makes them visible because they contain TWICE the amount of DNA
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Structure of Chromosomes Each chromosome consists of:
* CHROMATIDS – identical parts
- called “sister chromatids”
* CENTROMERE – point at which each chromatid are attached to each other
chromatid centromere
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Structure of Chromosomes (cont.) When the cell divides into 2 new cells –
the “sister chromatids” separate and each one goes into a new cell
Each chromosome consists a pair of chromatids (2)
Humans = 46 chromosomes
= 92 chromatids
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Cell Cycle The series of events that cells go through as
they grow and divide. During this cycle the cell:
1. grows
2. prepares for division
3. divides to form 2 “daughter” (identical) cells
Then each daughter cell prepares to
begin the cycle again
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Chromosome Quiz
1. Name the 2 substances that make up chromosomes. (2 points)
2. How many chromosomes do humans have? (1 point)
3. What is the function of chromosomes? (1 point)
4. At what point are chromosomes visible in the nucleus? Why? (2 points)
5. Draw and label a chromosome. (4 points)
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Events of the Cell Cycle
includes
is divided into is divided into
Cell Cycle
M phase (Mitosis)
Interphase
G1 phase S phase ProphaseG2 phase Metaphase TelophaseAnaphase
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Interphase Longest phase of the cell cycle
Known as the “in-between” period of growth
Divided into 3 Phases: G1, S, and G2
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G1 (Gap 1) Phase Cells do most of their growing during this
phase
Cells increase in size
Manufacturing of new proteins & organelles
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S (Synthesis) Phase Chromosomes are replicated
Synthesis of DNA molecules & Histones occur
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G2 (Gap 2) Phase Shortest of the phases
Organelles & molecules needed for cell division are produced
When this phase is complete, cells are ready for the M Phase (mitosis) and begin the process of cell division
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Mitosis The 1st stage of cell division in eukaryotic cells
Depending on type of cell, this phase can last from a few minutes to several days.
Divided into 4 phases
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Prophase The 1st & longest phase of
Mitosis (50 – 60%of whole
process) Chromatin condense to form
chromosomes Centrioles separate and move to
opposite sides of the nucleus structures called SPINDLES
begin to form – they help to separate chromosomes
Nucleolus disappears & nuclear envelope breaks down
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Metaphase Often last only a few
minutes
Chromosomes line up across the center of the cell
Each chromosome is connected to a spindle fiber at its centromere
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Anaphase The spindle fibers pull
apart the sister chromatids
Each chromatid becomes its own chromosomeand move towards the centrioles at opposite ends of the cell
The phase ends when the chromosomes reach the centrioles & stop moving
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Telophase Chromosomes lose their
distinct shapes
Nuclear envelope re-forms around each group of chromosomes
Spindle fibers disappear & a nucleolus becomes visible in each new nucleus
Mitosis is complete, but cell division is not
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Cytokinesis Cytoplasm pinches in half
Each daughter cell has an identical set of chromosomes from the parent cell
Usually occurs at the same time as telophase
Cell division is not complete until cytokinesis is complete
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Overview of Mitosis
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Cell Cycle Quiz 5-3-07 – 16 points1. Name the 3 phases of Interphase in order.
State the events that occur in each phase. (4 points)
2. What organelles are responsible for cell division? (1 points)
3. What is the longest phase in MITOSIS? (1 point)
4. What event ends cell division? (1 points)
5. What is the final result of Mitosis? (1 point)
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6. Label each picture with the correct phase of mitosis (8 points)
A B
CD
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Assignment Complete the following questions in your
notebook:
chapter assessment p. 257
#’s 3-7, 15-21, 28-34
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Homologous Chromosomes Chromosomes that
are in all sexually reproducing organisms
Occur in pairs2 identical chromosomes
= homologous chromosomes
same size and shape. are different than all
other chromosomes
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Diploid Cells Diploid Cells – contain both chromosomes of
a homologous pair
Human cell = 23 pairs of homologous chromosomes
2 x 23 = 46
Human Chromosome # = 46
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Haploid Cells Haploid Cells – contain only 1 chromosome
of a homologous pair
23 pairs of homologous chromosomes
1 x 23 = 23
**all egg & sperm cells = 23 chromosomes
ALSO KNOWN AS GAMETES
(egg)23 + (sperm) 23 = 46 chromosomes – human baby
Zygote – a new cell formed by a sperm & egg cell - has the normal number of chromosomes
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MEIOSIS
The process of reducing the number of chromosomes per cell in half
Separating homologous chromosomes in a diploid cell
Making a diploid (46) into a haploid (23)
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Process of Meiosis Involves 2 distinct divisions:
Meiosis I
Meiosis II
Begin with 1 diploid cell (46)
End with 4 haploid cells (23)
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Meiosis I Looks like MITOSIS
But in Meiosis I, each chromosome is paired with it corresponding HOMOLOGOUS CHROMOSOME
This forms a TETRAD – 4 chromatids
( 2 from each chromosome)
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Crossing Over
•When homologous chromosomes pair up to make tetrads – they exchange portions of their chromatids
•This is called CROSSING OVER
•This results in the exchange of genes between the homologous chromosomes
•This produces new combinations of genes
TETRAD
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RESULTS OF MEIOSIS I The chromosomes go through the same
phases as Mitosis Produces 2 new cells with 46 chromosomes
eachBUT ………………..
1. the new “daughter” cells DO NOT have identical sets of chromosomes like the parent
2. are different from each- because of crossing over & the separation of the homologous chromosomes
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Meiosis II The 2 cells from Meiosis I enter this
2nd division
Unlike Meiosis I – the 2 cells …..
do not replicate the chromosomes
The cells go through each phase just like in Meiosis I
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Results of Meiosis II 4 daughter cells that are haploid cells
Have only half of the # of chromosomes
All are different from each other
All are different from its parent cell
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Gamete Formation The making of reproductive cells MALE GAMETE = SPERM CELLS
Through meiosis – males produce 4 new sperm cells
FEMALE GAMETE = EGG CELLS (OVUM)
Through meiosis – females produce only 1 egg cell and 3 polar bodies (incomplete)
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Gregor Mendel
Read handout and section 11-1
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Probability & Punnett Squares
When Mendel realized when he crossed the pea plant to make hybrids he always had the same result :
75 % - dominant (3/4)
25% - recessive (1/4)
He realized that the Principle of Probability could be used to explain the results of genetic crosses.
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Probability The likelihood that a particular event will
occur Example – flipping a coin What is the probability that the coin will land
on heads? What is the probability that the coin will land
on tails? This relates to genetics because of the way
alleles segregate is completely random, like a coin flip.
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Punnett Square Used to predict & compare
the genetic variations that will result from a cross.
Shows the results of Mendel’s experiment
The letters inside & outside represent alleles
Outside = parents Inside = possible offspring
TT Tt
Tt tt
T
t
T t
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Punnett Squares (cont.)
Dominant allele – represented by CAPITAL LETTERS (T)
Recessive allele – represented by lower case letters (t)
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Homozygous alleles
2 identical alleles Know as the “True Breed”
Can be:
1. TT – homozygous dominant
2. tt – homozygous recessive
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Heterozygous Alleles
2 different alleles Known as “hybrids”
Can be only:
1. Tt
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Phenotype
Physical characteristics
What you see
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Genotype
Genetic make up What is located on DNA Tt , TT , or tt Tt & TT = tall
- each has the same phenotype but have different genotypes
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Punnett Square Activity
Create Punnett Square for the following crosses:
1. MM x mm 6. Bb x bb
2. Pp x Pp 7. FF x Ff
3. AA x AA
4. hh x HH
5. rr x rr
For each one write the results below each one
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Mendel & Punnett Square Quiz – 20 points1. Define Genetics.2. Define Heredity.3. Define Gene.4. Define Allele.5. State the Principle Of Dominance.6. The dominant allele is represented by _____.7. The recessive allele is represented by ___.8. Create a Punnett Square for each of thr
following. Make sure you state all information for each one:Gg x GG AA x aa Rr x Rr Bb x bb