Download Meiosis - Teachers TryScience

Vocabulary
Haploid cells (N) define a set of chromosomes
with only one copy in the cell, half the normal
number of chromosomes.
Diploid cells (2N) have both sets of the
homologous chromosomes
Homologous chromosomes are identical in form
and in the way their genes are arranged.
Traits are characteristics that are passed on from
parent to offspring.
1
Heredity is the passing of traits from parent to
offspring. This information that determines the
traits of an individual is carried on chromosomes.
Chromosomes are made up of a long molecule of
DNA covered with protein.
Each hereditary trait is controlled by one or more
segments of DNA. These segments are called
genes. Most of these function by providing the code
for the synthesis of proteins.
Because chromosomes divide equally during cell
division (mitosis), each daughter cell inherits a
complete set of these.
2
Mitosis is the process of cell division in which
the chromosomes in the nucleus of the parent
cell are duplicated and divide into 2 identical
sets. Then in cytokinesis the entire nucleus
divides, the two cells divide into daughter cells.
The major significance of mitosis is that is
ensures genetic continuity.
3
DNA appears as tangled mass of chromatin that thickens and
double to become chromosomes.
4
• Interphase is divided into 3 parts:
• G1 Phase – rapid growth and centrioles
replicate
• S Phase – DNA synthesis Chromosomes
double and you go from 46 to 92
• G2 Phase – organelles duplicate
5
Prophase – You see visible chromosomes,
The nuclear membrane breaks down and
disappears. Centrioles start moving apart pulling
the spindle fibers across the cell.
6
7
Metaphase: Chromosomes are lined up across the
middle of the cell. Spindle is football shaped and it is
thought to be attached to the centromeres and helps
to separate the chromosomes in the next phase.
8
• Anaphase: rips chromosomes in ½.
• Chromatids travel to the poles.
9
• Telophase: 2 new cells
• Nucleus and nuclear membrane reappear.
10
Plant cells have a cell plate form between 2 new
cells. Then they separate into daughter cells.
Plants do not have asters or centrioles. They do
have cell walls and cell plates.
In most cases living things grow because it
produces more cells.
Humans have 46 chromosomes.
11
12
Meiosis
It is defined as a process of reduction
division in which the number of
chromosomes per cell is cut in half
through the separation of
homologous chromosomes in a
diploid cell.
13
Stages of Meiosis
Prophase I – You see visible chromosomes,
The nuclear membrane breaks down and
disappears. Centrioles start moving apart pulling
the spindle fibers across the cell.
Each chromosome lines up with its
corresponding homologous chromosome to
form a structure called a tetrad and crossingover occurs.
14
Prophase I – You see visible chromosomes,
The nuclear membrane breaks down and
disappears. Centrioles start moving apart pulling
the spindle fibers across the cell.
15
• Teacher please hand out yarn tied into x’s.
16
Twist the yarn together. This is synapsis,
crossing-over, of corresponding homologous
chromosomes.
17
After crossing-over alleles have been switched. This genetic
recombination results in genetic variation. Parents have a different set of
alleles and genes than their offspring do.
18
Metaphase I: Homologous Chromosomes are lined up
across the middle of the cell.
19
• Anaphase I : Homologous chromosomes
segregate and travel to the poles.
20
• Telophase I : 2 new cells (Diploid 2N 46
chromosomes.)
• Nucleus and nuclear membrane reappear.
21
Cytokinesis:
Ends with 2 new cells 46 chromosomes each
22
Prophase II starts with 2 cells
23
Metaphase II
24
25
26
4 1N haploid gametes
27