1. Chapter 10 Meiosis
Textbook pages

2. Reproduction Reproduction - process of producing offspring.
Some offspring are produced by two parents.
Some offspring are produced by just one parent.
Whether an organism is identical or similar to its parent is determined by the way the organism reproduces.

3. Asexual Reproduction Production of identical offspring: Mitosis
Binary Fission
Budding
Today were going to talk about sexual reproduction at the cellular level.

4. Sexual Reproduction Practiced by most eukaryotic organisms
In sexual reproduction, two parents give genetic material to produce offspring that are genetically different from their parents.
Each parent produces gametes (reproductive cell); sperm and eggs.
A gamete from one parent fuses with a gamete from the other parent to form a zygote.
This process is called fertilization.

5. Germ Cells & Somatic Cells
Germ cells (gametes) are cells that are specialized for sexual reproduction (sperm & egg).
Somatic cells are all other body cells. They DO NOT participate in sexual reproduction.

6. CHROMOSOMES:
All cells contain chromosomes. There are two types of chromosomes found in the nucleus of cells:
autosomes
sex chromosomes
Your body cells contain 23 pairs of
homologous chromosomes:
23 chromosomes from your mom, and
23 chromosomes from your dad

7. NEW Term!
Homologous chromosomes are chromosomes that make up a pair; one from each parent
Are the same length
Have the same genes

8. Your body cells contain 23 pairs of homologous chromosomes:
For each homologous pair, one chromosome comes from
mom and one comes from dad.

10. LOOK AT THE KARYOTYPE BELOW:
Chromosome pairs 1-22 are autosomes.
The 23rd pair are the sex chromosomes: X and Y which determine gender:
XX =
XY =
female
male

11. Haploid vs. Diploid
Cells that are diploid (somatic cells) have two sets of chromosomes (2n)
Cells that are haploid (gametes) have one set of chromosomes (n)

12. Body Cells
- somatic cells
- diploid (2n)
Diploid (2n) cells – have two copies
of every chromosome
- half the chromosomes come from each parent
Gametes
- sex cells (sperm and egg)
- have DNA that can be
passed to offspring
- haploid (n)
Haploid (n) cells – have one copy of each chromosome
- gametes have 22 autosomes and 1 sex chromosome

13. Key Terms Diploid refers to complete chromosome sets in a cell (or 2N)
N= the number of chromosomes in a gamete (sex cell)
N chromosomes from the female parent + N chromosomes from the male parent= 2N
For humans, 2N = 46

14. Key Terms Haploid refers to single chromosomes in a cell (or N)
One-half of the 2N set (the maternal N or the paternal N)
Gametes (i.e. sperm, egg sex cells) are haploid cells
For humans, N = 23

15. Bottom Line
diploid means there are the full number of chromosomes in cells
haploid means that there are half the number of chromosomes in cells

17. MITOSIS AND MEIOSIS

18. Mitosis and meiosis are types of nuclear division that
make different types of cells.
Meiosis
- occurs in sex cells
- Makes 4 haploid cells from diploid cells
- produces gametes
Mitosis
- occurs in somatic cells
- makes more diploid cells
We already talked about mitosis, so lets move on to meiosis.
Make a Venn diagram to compare and
Contrast Mitosis and Meiosis!

19. MEIOSIS 10-1 Making gametes…
Making gametes…

20. Meiosis reduces the chromosome number and creates genetic diversity.
Cells go through two rounds of division in meiosis:
Meiosis I and Meiosis II - each round has four phases
Meiosis I – pairs of homologous chromosomes separate
Meiosis II – sister chromatids divide
homologous chromosomes
sister
chromatids

21. Meiosis Interphase Occurs….
Replication of DNA
Chromatin condenses
Sounds familiar right???

22. Meiosis I
Occurs after DNA has been replicated in interphase
Divides homologous chromosomes in four phases:
prophase I  metaphase I  anaphase I  telophase I
After cytokinesis, two cells are produced with one homologous
chromosome in each

23. PROPHASE I Homologous chromosomes pair up Crossing over occurs
Nuclear envelope breaks down
Spindles form

24. Crossing Over Creates Genetic diversity
What is Crossing Over?
Chromosomal segments (genetic information) are exchanged between a pair of homologous chromosomes
Crossing Over Creates Genetic diversity

25. Which set of chromatids illustrates the result of a single crossover of the homologous chromosomes?

26. METAPHASE I Spindle fibers attach to the centromeres
Homologous Chromosomes Line up at the equator
chromosome pairs line up randomly in cell

27. ANAPHASE I
Homologous chromosomes separate and move to the opposite poles of the cell

28. TELOPHASE I The cell divides
The result is two. 2 Haploid daughter cells with exchanged genetic information
The daughter cells are not genetically identical
**During Telophase I Cytokinesis occurs at the same time!!**

29. Review Meiosis I Telophase I Interphase I Prophase I Metaphase I
Anaphase I .
Telophase I
Homologous Chromosomes – humans have 46 chromosomes
- 23 from Mom
- 23 from Dad
= 23 pairs
The chromosomes that make up a pair (one from each parent) are called homologous chromosomes.
- have the same length
- have same centromere position
- carry genes that control the same traits

30. Meiosis II
Meiosis II divides sister chromatids in four phases:
prophase II  metaphase II  anaphase II  telophase II
After cytokinesis, four new cells are produced, each with half
the chromosome number (haploid)

31. Nucleus breaks up
Spindles form and attach to centromere

32. Sister chromatids randomly align at middle of cell

33. Sister chromatids separate
Chromosomes move to opposite poles of cell

35. Cells divide
4 haploid daughter cells result
Each cell is genetically different

36. Review Meiosis II Prophase II Metaphase II Anaphase II Telophase II.
Process of Meiosis II is very similar to Mitosis.

37. How Meiosis was Discovered
The Stages of Meiosis
How Meiosis Works

38. Meiosis Animation

39. Haploid cells develop into mature gametes:
Gametogenesis - the production of gametes
- differs between females and males
Sperm become streamlined and mobile
with the addition of flagella
Sperm primarily contribute DNA to an
embryo
Eggs contribute DNA, cytoplasm and
organelles to an embryo
HONORS ONLY
During meiosis, the egg gets most of
the contents
The other cells form polar bodies

40. Sources of Variations and Differences
1. Crossing over
occurs during prophase I
homologous chromosomes swap pieces
this chromosome swapping creates variations
2. Random assortment of chromosomes
chromosome pairs line up randomly in cell
when the pairs separate, this creates cells with
genetic variations
3. Fertilization
which sperm gets to the egg first??
it is random and can create variations in
offspring

41. Meiosis
Mitosis

44. Warm-up What is made during Mitosis??? What is made during Meiosis??
What are the phases of Meiosis?

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or try

46. Videos that show side by side view

47. ZYGOTE = 46 + 46 = 92 CHROMOSOMES =
WHY MEIOSIS?
MITOSIS – RESULTS IN GENETICALLY IDENTICAL OFFSPRING – INCLUDING THE # CHROMOSOMES
WHAT WOULD HAPPEN IF THE EGG AND SPERM HAD THE SAME # OF CHROMOSOMES AS THE BODY CELLS?
EGG = 46 CHROMOSOMES SPERM = 46 CHROM.
ZYGOTE = = 92 CHROMOSOMES =
NOT HUMAN

48. Mitosis Animation

49. Meiosis Animation