1. 11-4 Meiosis

2. Understanding Chromosomes in Humans
Chromosomes in Human Cells
Where did we get our 46 chromosomes?
From our parents
How many did you get from your father? 23
How many did you get from your mother?
We often say that you got a set of chromosomes (23) from your mother and a set of chromosomes (23) from your father.

3. Homologous Chromosomes
Chromosomes in Human Cells
The set from your mother and the set from your father are called homologous chromosomes!
Why are they called homologous?
Because each set contains the same (homo) basic genetic information.

4. Homologous Chromosomes
Blue eye
gene
Brown eye
gene
From Mom
From Dad
Blonde
hair gene
Brown hair gene

5. Human cell with all its chromosomes
cytoplasm
nucleus

6. Introduction to Meiosis
Process by which sex cells (gametes) are formed
sperm cells or pollen cells (male cells)
egg cells (female cells)
Cell division of sex cells whereby, homologous chromosomes are separated

8. Phases of Meiosis Interphase Prophase I Metaphase I Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase II

10. Chromosome Number Terminology
Diploid
Two sets of chromosomes.
Cell contains homologous pairs from both parents 2N
Humans = 46
Haploid
One set of chromosomes.
Cell (gametes or sex cells) contains one set of chromosomes 1N
Humans = 23

11. Meiosis I – separation of homologous chromosomes
Interphase I
Prophase I
Metaphase I
Anaphase I
Cells undergo a round of DNA replication, forming sister chromatids.
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
Spindle fibers attach to the chromosomes.
The fibers pull the homologous chromosomes toward the opposite ends of the cell.
Go to Section:

12. Meiosis I – separation of homologous chromosomes
Interphase I
Prophase I
Metaphase I
Anaphase I
Cells undergo a round of DNA replication, forming sister chromatids.
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
Crossing over occurs!!
Spindle fibers attach to the chromosomes.
The fibers pull the homologous chromosomes toward the opposite ends of the cell.
Go to Section:

13. Crossing-Over A = blonde hair a = brown hair
C = blue eyes c = brown eyes
Go to Section:

14. Crossing-Over A = blonde hair a = brown hair
C = blue eyes c = brown eyes
Go to Section:

15. Crossing-Over A = blonde hair a = brown hair
C = blue eyes c = brown eyes
Go to Section:

16. Meiosis I – separation of homologous chromosomes
Interphase I
Prophase I
Metaphase I
Anaphase I
Cells undergo a round of DNA replication, forming sister chromatids.
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
Crossing over occurs!!
Spindle fibers attach to the chromosomes.
The fibers pull the homologous chromosomes toward the opposite ends of the cell.
Go to Section:

17. Meiosis I – separation of homologous chromosomes
Interphase I
Prophase I
Metaphase I
Anaphase I
Cells undergo a round of DNA replication, forming sister chromatids.
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
Crossing over occurs!!
Spindle fibers attach to the chromosomes.
The fibers pull the homologous chromosomes toward the opposite ends of the cell.
Go to Section:

18. Meiosis II – separation of chromatids
Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Go to Section:

19. Meiosis II – separation of chromatids
Figure Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Go to Section:

20. Meiosis II – separation of chromatids
Figure Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Go to Section:

21. Meiosis II – separation of chromatids
Figure Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Go to Section:

22. Meiosis II – separation of chromatids
Figure Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Go to Section:

23. Gamete Formation Males sperm cells (1N) pollen cells (1N) Females
egg cells (1N)
polar bodies
those cells that do not participate in reproduction
result from unequal division of the cytoplasm

24. Gamete Formation
Polar body
Polar body