6.1 cell division

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What you’ll learn about in this unit:
 Why and how cells divide
 The three types of cell division:
Binary Fission, Mitosis and Meiosis
 What regulates or controls when cells
start and stop dividing.
 How cells specialize during their life
 Mistakes that occur during division
that can lead to cancer and genetic
disorders
Unit 5 Cell Division
Key Concept: All cells come from preexisting cells –
Cell Theory
Cell division – process by which cells produce new cells
3 Types of Cell Division:
Prokaryotes (Bacteria)
Eukaryotes (Animals, Plants, Fungi, Protists)
Binary Fission
Mitosis
Meiosis
Purpose of Cell Reproduction
/Division
 Create new cells that contain the genetic
material (DNA) stored in chromosomes.

Purpose of Cell Division
1. Binary Fission – Creates 2 genetically identical new
organisms by asexual reproduction
2. Mitosis – Creates somatic / body cells
Ex. Skin, nerve, blood
Used for growth, to repair damage or replace worn
out cells
3. Meiosis – Creates gametes / sex cells
Used for sexual reproduction
Chromosomes
When a new cell is made it must receive a
copy of the genetic material from the parent
cell.
Chromosomes are made of the DNA
(genetic info) and“carry” it from a parent cell
to the daughter cells.
Chromosome Location in Cells
 Eukaryotic cells – Nucleus
 Prokaryotic cells– Cytoplasm (Nucleoid Region)
Chromosome Shape
 Eukaryotic cells - Rod , Linear
 Prokaryotic cells – Circular
Chromosome Structure
 2 Types of Molecules joined together
1. DNA (nucleic acid) 1 in each chromosome
2. Histones (protein) 1000’s in each chromosome
Two Types of Chromosomes
 Autosomes – carry genes not related to sex
 Sex chromosomes – carry genes for sex traits
XX – Female
XY - Male
Homologous Chromosomes
Homologous Chromosome Pair
hair color
eye color
skin color
 One autosome from each parent
 Same size and shape
 Similar but not identical genes
Sex chromosomes are NOT homologous
because they carry different genes
Body Cells and Sex Cells have different
numbers of chromsomes
Somatic / Body Cells
 Have 2 copies of each chromosome 1 from
each parent – Diploid 2n
 Members of a species have the same
chromosome number in body cells
Ex. Humans 46 Dogs 78 Fruit Flies 4
 Made through Mitosis
Body Cells and Sex Cells have different
numbers of chromsomes
Gametes / Sex Cells
 Have only 1 copy of each chromosome Haploid 1n
 Made through Meiosis
Haploid 1n
Diploid 2n
3 Major Types of Cell Division
Binary Fission
* Used by Prokaryotes and some unicellular Protists
* Makes two genetically identical daughter cells
(clones)
 Form of asexual reproduction
Mitosis
 Used by eukaryotic organisms
 Process of making somatic/ body cells
 Ex Skin , nerve, muscle
 Used for growth, to repair damage or
replace worn out cells
 2 Daughter cells are created from the
division on one parent cell
 Daughter cells are genetically identical to
the parent cell –they “inherit” an exact
copy of the same chromosomes
Mitotic Cell Division
X= Number of chromosomes
Parent Cell
X
X
X
Daughter Cells
Meiosis
 Used by sexually reproducing eukaryotics.
 Process of making gametes/ sex cells.
 4 new cells are made from one parent cell.
 New cells are NOT genetically identical to
the parent cell.
 Daughter cells have only half the number of
chromosomes as the parent cell.
 Also known as Reduction Division
Meiotic Cell Division
X= Number of chromosomes
Parent Cell
½X
½X
½X
½X
X
Daughter Cells
Gametes are made in Meiosis
 DNA in threadlike form – Chromatin
 DNA in coiled /condensed form - Chromosome
Chromosome number is different in sex cells and body cells
• Haploid (n) cells have only 1 copy of each type of
chromosome
•
- Sex cells are haploid
• Diploid (2n) cells have 2 copies of each type of chromosome.
– Body cells are diploid.
The zygote (fertilized egg) doubles its
chromosomes and divides millions of times
resulting in growth.
Each new cell receives a complete set of all
the chromosomes
Meiosis occurs in the testicles and ovaries.
– Produces sex cells: egg and sperm.
– Sex cells are what transport/carry the parents DNA to
their kids
body cells
sex cells (sperm)
sex cells (egg)
• Haploid (n) cells have one copy of every chromosome.
– Gametes are haploid.
– Gametes have 22 autosomes and 1 sex chromosome.
• Chromosome number must be maintained in animals.
• Many plants have more than two copies of each
chromosome.
• Mitosis and meiosis are types of nuclear division that
make different types of cells.
• Mitosis makes
more diploid cells.
• Meiosis makes haploid cells from diploid cells.
– Meiosis occurs in sex cells.
– Meiosis produces gametes.
Cell Division Vocabulary
 diploid (2N) – a cell with 2 chromosome
sets in each of its cells; all body (somatic)
cells
 haploid (N) – a cell with 1 chromosome set
in each of its cells; all gametes (sperm, eggs)
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