1. Chapter 7
Meiosis

2. Meiosis is a form of cell division that
Halves the number of chromosomes
When forming specialized
Reproductive cells.

3. http://highered. mcgraw-hill

4. Meiosis involves 2 divisions of the
Nucleus - meiosis I and meiosis II -
And each division is subdivided
Into prophase, metaphase,
Anaphase and telophase stages.
Before meiosis begins, the DNA in the
Original cell is replicated.

5. There are 8 stages to Meiosis…
Step 1 - Prophase I
Step 2 - Metaphase I
Step 3 - Anaphase I
Step 4 - Telophase I
Step 5 - Prophase II
Step 6 - Metaphase II
Step 7 - Anaphase II
Step 8 - Telophase II

7. In prophase I, the chromosomes Condense, and the nuclear envelope
Breaks down. Homologous chromosomes
Pair all along their length and then
Cross-over. (crossing over occurs when
Portions of a chromatid on 1
Chromosome are broken and exchanged
With the corresponding portions
On one of the chromotids of the
Other chromosome.

9. In metaphase I, the pairs of Homologous chromosomes are moved
By the spindle to the equator
Of the cell.

10. In anaphase I, the homologous Chromosomes separate.
(just like mitosis)
But the chromatids do not separate
At their centromere! Each chromosome
Is still composed to 2 chromatids.

11. In telophase I, individual chromosomes
Gather at each of the poles. Then
Cytokinesis occurs forming 2 cells.

12. Now we get into mitosis II. The Chromosomes do not replicate
Between mitosis I and II!!
In prophase II, a new spindle forms
Around the chromosomes.

13. In metaphase II, the chromosomes Line up along the equator and are
Attached at their centromeres
To the spindle fibers.

14. In anaphase II, the centromeres Divide, and the chromatids
(now called chromosomes) move to
Opposite poles of the cell.

15. And lastly in telophase II, a nuclear
Envelope forms around each set of
Chromosomes. The spindle breaks
Down, and the cell undergoes
Cytokinesis.

16. The result of meiosis is 4 The 4 resulting cells are the
Haploid cells.
The 4 resulting cells are the
Reproductive cells.

17. The chromosome pairs separate Independently.
The chromosomes that an offspring
Receives from each pair is
A matter of chance.
The random distribution of homologous
Chromosomes during meiosis is called
Independent assortment.

18. Meiosis and the joining of gametes Are essential to evolution.
The DNA exchange that occurs at
Crossing over adds even more
Recombination to the independent
Assortment of chromosomes that
Occurs later in meiosis.
Thus the number of genetic
Combination that can occur among
Gametes it practically unlimited.

19. The process by which sperm are Produced in male animals is
Called spermatogenesis.
The process by which gametes are
Produced in female animals is
Called oogenesis.
Meiosis for males creates 4 cells,
But only 1 cell in females.

21. Some organisms look exactly like Their parents and siblings.
7-2 Sexual Reproduction
Some organisms look exactly like
Their parents and siblings.
These traits are passed down
In 2 ways, asexual and sexual
Reproduction.

22. In asexual reproduction, a single Parent passes copies of all of
Its genes to each offspring,
Basically creating a clone.
In sexual reproduction, 2 parents
Each form haploid cells, which join
To form offspring.

23. Asexual reproduction is the simplest And most primitive
Method of reproduction.
But it allows organisms to produce
Many offspring in a short period
Of time.
But the DNA does not vary much
Between individuals.

24. The entire span in the life of an Organism from one generation
To the next is called a life cycle.
Eukaryotes that undergo sexual
Reproduction can have one of three
Types of sexual life cycles:
Haploid
Diploid
Alternation of Generations

25. The haploid life cycle is the simplest.
Haploid cells occupy the major
Portion of the life cycle, the zygote
Is the only diploid cell and it
Undergoes meiosis immediately
After creation.
This type is usually found in protists,
Or fungus.

26. The diploid life cycle is the one That we live in.
Most of the life cycle is diploid,
With haploid cells only for
Reproduction.
The haploid gametes join in a
Process called fertilization, which
Results in a diploid zygote.

27. Plants, algae and some protists Have a life cycle that regularly
Alternate between haploid
And diploid.
The diploid phase of a plant is
Called a sporophyte, while a spore
Is haploid.
The gametophyte is the haploid
Phase of a plant.

28. LET'S SUM
IT UP!

29. Steps of Meiosis I Reductional In humans, n=23, so 2n=46. Division !
n=23 in humans

30. Steps of Meiosis II

33. THE END