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Biology Chapter 11 Section 4 Meiosis

Miller Levine Dragonfly Book
by

Mark Meredith

on 30 August 2015

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Transcript of Biology Chapter 11 Section 4 Meiosis

Meiosis
Gametogenesis
END OF SECTION
Mitosis
results in the production of two genetically identical diploid cells.

Meiosis
produces four genetically different haploid cells.
Comparing Mitosis and Meiosis
In male animals, meiosis results in four equal-sized gametes called sperm.
Gamete Formation
MEIOSIS II
Metaphase II
The chromosomes line up in the center of cell.
Phases of Meiosis
MEIOSIS I
Telophase I and
Cytokinesis
Nuclear membranes form.
The cell separates into two cells.

The cells are now haploid.

Each new cell has copies of each chromosome attached by the
centromere
.
Phases of Meiosis
MEIOSIS I
Metaphase I
Spindle fibers attach to the chromosomes.
Phases of Meiosis
Crossing Over
When homologous chromosomes form tetrads in meiosis I, they exchange portions of their chromatids in a process called
crossing-over
.

Crossing-over
produces
new combinations
of alleles.
Phases of Meiosis
Interphase
Cells undergo a round of
DNA replication
, forming duplicate chromosomes.
Phases of Meiosis
Phases of Meiosis
Meiosis involves two divisions:
meiosis I
meiosis II





By the end of meiosis II, the diploid cell that entered meiosis has become
4 haploid cells
.
Meiosis
is a process in which the
number of chromosomes per cell is cut in half

through the
separation of homologous chromosomes
in a diploid cell.
Phases of Meiosis
A cell that contains both sets of homologous chromosomes is said to be
diploid
or
2N
.

For Drosophila, the diploid number is 8, which can be written as 2N=8.

What is the diploid number for humans? 2N=
Chromosome Number
Each organism must inherit a single copy of every gene from each of its “parents.”

Gametes
are formed by a process that separates the two sets of genes so that
each gamete ends up with just one set
.
Compared to egg cells formed during meiosis, daughter cells formed during mitosis are
genetically different, while eggs are genetically identical.
genetically different, just as egg cells are.
genetically identical, just as egg cells are.
genetically identical, while egg cells are genetically different.
11-4
The formation of a tetrad occurs during
anaphase I.
metaphase II.
prophase I.
prophase II.
11-4
During meiosis, the number of chromosomes per cell is cut in half through the separation of
daughter cells.
homologous chromosomes.
gametes.
chromatids.
11-4
If the body cells of humans contain 46 chromosomes, a single sperm cell should have
46 chromosomes.
23 chromosomes.
92 chromosomes.
between 23 and 46 chromosomes.
11-4
In many female animals, only one egg results from meiosis.

The other three cells, called
polar bodies
, are usually not involved in reproduction.
Gamete Formation
MEIOSIS II
Telophase II and Cytokinesis
Meiosis II results in
four haploid (N) daughter cells
.
Phases of Meiosis
MEIOSIS II
Anaphase II
The
sister chromatids separate
and move toward opposite ends of the cell.

What held them together?
Phases of Meiosis
MEIOSIS II
Prophase II
Meiosis I resulted in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell.
Phases of Meiosis
Telophase I and Cytokinesis I
Anaphase II
Metaphase II
Prophase II
Telophase II and Cytokinesis
Meiosis II
Phases of Meiosis
Meiosis II
The two cells produced by meiosis I now enter a second meiotic division.

Unlike meiosis I, neither cell goes through chromosome/DNA replication.
Phases of Meiosis
MEIOSIS I
Anaphase I
The fibers pull the homologous chromosomes toward opposite ends of the cell.
Phases of Meiosis
MEIOSIS I
Prophase I
Each chromosome pairs with its corresponding
homologous chromosome
to form a
tetrad
.
Phases of Meiosis
Gametes contain only a single set of chromosomes.



These cells are
haploid
. Haploid cells are represented by the symbol
N
.

For Drosophila, the haploid number is 4, which can be written as N=4.

What is the human haploid number? N=
Chromosome Number
These sets of chromosomes are
homologous
.
Chromosome Number
All organisms have different numbers of chromosomes.

A body cell in an adult fruit fly has 8 chromosomes:
4 from the fruit fly's male parent, and
4 from its female parent.
Chromosome Number
11-4 Meiosis
In many female animals, meiosis results in the production of
only 1 egg.
1 egg and 3 polar bodies.
4 eggs.
1 egg and 2 polar bodies.
11-4
Interphase I
Telophase I and Cytokinesis
Anaphase I
Metaphase I
Prophase I
Meiosis I
Phases of Meiosis
How would you expect the human number to compare to other primates?
Why is this step necessary?
Why are new combinations good for a species?
Why not replicate DNA again?
Notice that each cell still has
2 copies of each gene.
Why then call it haploid?
When were these copies made?
Spermatogenesis
Oogenesis
What are the 2 main accomplishments of meiosis?
Full transcript