Download diploid cells


Demonstrate understanding of the
following terms.
› Chromosome
› Chromatid
› Chromatin

Produces offspring that are genetically
different from parents.

Accomplished by gametes (sex cells) –
one male and one female. Formed
during meiosis.

Somatic cells are diploid cells – they
have 2 copies of each chromosome
(homologous pairs- 1 from mom, 1 from
dad).

Gametes (sex cells) are haploid cellsthey have only 1 copy of each
chromosome from each pair.

Because of meiosis, the chromosome number
of a species is maintained even after
fertilization.

Cells go through 2 divisions
› Meiosis I
› Meiosis II

Meiosis results in 4 new cells rather than 2
(mitosis)

The chromosome number is reduced by
half in the 4 new cells.

DNA coils tightly into
chromosomes

Spindle fibers appear

The nucleolus and
nuclear membrane
disappear.

Synapsis occurs
(Tetrads formed)
Source: HOPES: An Introduction to DNA and Chromosomes
http://hopes.stanford.edu/basics/dna/b7.html

Crossing-over occurs =
genetic variability

The homologous
chromosome pairs line
up randomly along the
middle of the dividing
cell.

Spindle fibers from one
pole attach to one
chromosome, while
spindle fibers from the
opposite pole attach
to the other
chromosome.
Source: HOPES: An Introduction to DNA and Chromosomes
http://hopes.stanford.edu/basics/dna/b7.html

Each chromosome
moves to opposite
poles of the dividing
cell.

Random separation
= independent
assortment.
Source: HOPES: An Introduction to DNA and Chromosomes
http://hopes.stanford.edu/basics/dna/b7.html

The chromosomes
reach opposite ends
of the cell and
cytokinesis begins.

The new cell
contains half the
number of
chromosomes as the
original cell.
Pearson Biology Coach: Meiosis I Animation
Pearson Biology Coach Activity

Meiosis I is known as
a “reduction
division” because
the number of
chromosomes is
reduced by ½.

Meiosis II is known as
an “equation
division” because
the number of
chromosomes is the
same at the end of
meiosis II as at the
end of meiosis I.

No copying of DNA
takes place before
Meiosis II.

In some species,
meiosis II begins after
nuclear membrane
forms in the new cells.
In other species,
meiosis II begins right
after cytokinesis.

The spindle fibers
appear and begin to
move the
chromosomes
toward the middle of
the cell.
Source: “Cell Division, Mitosis and Meiosis Lecture Notes .” Professor
Michael Muller.
http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect16.htm

Each chromosome is
located at the
middle of the cell
with each chromatid
facing opposite
poles.
Source: “Cell Division, Mitosis and Meiosis Lecture Notes .”
Professor Michael Muller.
http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect16.htm

The chromatid
separate and move
toward opposite
poles of the cell.
Source: “Cell Division, Mitosis and Meiosis Lecture Notes .”
Professor Michael Muller.
http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect
16.htm

Nuclear membrane
re-forms around
chromosomes in
each of 4 new cells.

Cytokinesis results in
4 new cells each
which contains ½ the
number of
chromosomes as
parent cell.
Pearson Biology Coach Meiosis II Animation
Source: “Cell Division, Mitosis and Meiosis Lecture Notes .” Professor Michael
Muller.
http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect16.htm
Assembling the Stages of Meiosis II

Meiosis occurs in the testes of males and
the ovaries of females.

In the formation of male gametes, the
original cell in testes produces 4 sperm
cells by meiosis.

In the formation of female gametes, the
original cell in the ovary produces 1 egg
and 3 polar bodies by meiosis.

What types of cells are made by
meiosis?

How many cells are made at the end?

Are they the same/different as parent?

What happens to chromosome number?

What types of cells are made by
meiosis?

How many cells are made at the end?

Are they the same/different as parent?

What happens to chromosome number?

Why is meiosis important?