Download Chapter 10.2

MEIOSIS
Chapter 10.2
Chromosomes
2
Normal human body cells each contain 46
chromosomes.
Body Cells are produced by mitosis

Produces daughter cells that are virtually identical
to the parent cell.
Contain two copies of each chromosome
Gametes are produced by meiosis


 Eggs
& Sperm
 Contain one copy of each chromosome
Diploid & Haploid Cells
3
Diploid (2n)= a cell with two of each kind
of chromosome

Normal

body cells are diploid
Haploid (n)= a cell with one of each kind
of chromosome
 Gametes
are haploid
Homologous Chromosomes
4


Homologous chromosomes = paired chromosomes in
diploid cells
Each chromosome is made up of two sister chromatids
Meiosis
5
When cells divide by mitosis, the new cells have
exactly the same number and kind of chromosomes
as the original cells.
Meiosis produces daughter cells containing half the
number of chromosomes (haploid cells) as the parent
cell – gametes

Female
gametes = eggs
Male gametes = sperm
Sexual reproduction: When a sperm cell fertilizes
the egg, the resulting cell is called a zygote.
Zygotes are diploid because they contain all of
the chromosomes from the egg and the sperm.

Process of Meiosis
6

Meiosis is made up of two cell divisions
 Prophase
1
 Metaphase 1
 Anaphase 1
 Telophase 1
 Prophase
2
 Metaphase 2
 Anaphase 2
 Telophase 2
Prophase 1
7

Similar to Prophase in mitosis
 Chromosomes
and spindle form, nuclear membrane
disappears


Homologous chromosomes pair up & form tetrads
Crossing over occurs – homologous chromosomes
exchange genetic information
Metaphase 1
8


Chromosome centromeres are attached to the
spindle
Homologous chromosomes are lined up in the
middle of the cell as tetrads
Anaphase 1
9


Homologous chromosomes are separated and
pulled to opposite ends of the cell
This step ensures that each new cell will receive only
one chromosome from each homologous pair.
Telophase 1
10




The spindle is broken down
Chromosomes uncoil
Cytoplasm divides
Each new cell has half of the genetic information of
the original cell
Prophase 2
11


Chromosomes coil
A spindle forms in each new cell & spindle fibers
attach to chromosomes
Metaphase 2
12


Chromosomes are lined up in the center of the cell
Looks similar to metaphase in mitosis
Anaphase 2
13


The centromere of each chromosome splits
Sister chromatids are separated & pulled to
opposite ends of the cell
Telophase 2
14


Cytoplasm divides, nuclear envelope reforms,
spindle breaks down
Similar to mitosis & telophase 1
After Meiosis
15

Four haploid gametes have formed from the one
original diploid cell
 Each
daughter cell contains 1 chromosome from each
homologous pair

Gamete formation is different in males & females
 Males
– 4 sperm are produced
 Females – 1 egg and 3 polar bodies are produced
 Cytoplasm
is divided unevenly
Genetic Variation
16

Meiosis helps to produce new genetic combinations.
 Crossing
over
 Random separation of homologous chromosomes


The number of different genetic combinations any
egg or sperm can produce is more than 8 million
When fertilization occurs, 70 trillion different
zygotes are possible.