Cell Division Unit

Chapter 10 Section 2

Chapter 11 Section 4

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

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

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

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

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

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

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

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)

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

G1 (Gap 1) Phase Cells do most of their growing during this

phase

Cells increase in size

Manufacturing of new proteins & organelles

S (Synthesis) Phase Chromosomes are replicated

Synthesis of DNA molecules & Histones occur

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

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

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

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

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

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

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

Overview of Mitosis

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)

6. Label each picture with the correct phase of mitosis (8 points)

A B

CD

Assignment Complete the following questions in your

notebook:

chapter assessment p. 257

#’s 3-7, 15-21, 28-34

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

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

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

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)

Process of Meiosis Involves 2 distinct divisions:

Meiosis I

Meiosis II

Begin with 1 diploid cell (46)

End with 4 haploid cells (23)

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)

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

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

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

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

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)

Gregor Mendel

Read handout and section 11-1

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.

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.

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

Punnett Squares (cont.)

Dominant allele – represented by CAPITAL LETTERS (T)

Recessive allele – represented by lower case letters (t)

Homozygous alleles

2 identical alleles Know as the “True Breed”

Can be:

1. TT – homozygous dominant

2. tt – homozygous recessive

Heterozygous Alleles

2 different alleles Known as “hybrids”

Can be only:

1. Tt

Phenotype

Physical characteristics

What you see

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

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

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