1. Chapter 11-4: Meiosis

2. Genes are lined up on chromosomes
Chromosomes occur in pairs in body (somatic) cells
1 pair from mother
1 pair from father
diploid cell (2n)
cell with 2 of each kind of chromosome

3. Organisms produce gametes (sex cells)
contain 1 of each kind of chromosome
haploid cell (n)
one of each kind of chromosome

4. Homologous Chromosomes
Paired chromosomes
2 chromosomes of each pair in a diploid cell
each have a corresponding chromosome from the opposite sex parent

5. Meiosis
# of chromosomes per cell is cut in half through separation of homologous chromosomes
cell division that produces gametes (sex cells)
has ½ the number of chromosomes as the parent
involves 2 cell divisions (I and II)

7. Haploid cells produced are sex cells or gametes
Sperm: male gametes (n)
4 equal-sized
Egg: female gametes (n)
1 large egg cell; 3 small polar bodies

8. Sperm + egg = fertilization (n + n = 2n)
Fertilized egg called a zygote
Zygote goes through mitosis to develop into a multicellular organism
Meiosis produces genetic variation
Genetic recombination
Reassortment of chromosomes
Basis for evolution (change through time)

9. Meiosis I: Interphase Begins with a diploid cell
cell replicates its chromosomes
Consists of 2 identical sister chromatids

10. Prophase I DNA coils up and spindle forms
Homologous chromosomes line up with each other to form a tetrad
Tetrad: consists of 2 homologous chromosomes, each made up of 2 sister chromatids
Pair up tightly (very tightly)

11. Crossing-Over
Non-sister chromatids from homologous chromosomes can break and exchange genetic material
Can occur anywhere on a chromosome and at several locations at the same time
Exchange of genetic material

13. Crossing-over provides genetic variation
Increases variability of organisms
Sometimes chromosomes fail to separate correctly
Called nondisjunction
Can lead to extra chromosomes or not enough chromosomes

14. Metaphase I
Spindle fibers pull tetrads to middle of a cell and line up together
Anaphase I
Homologous chromosomes separate and move to opposite ends of the cell
Telophase I
Chromosomes uncoil and cytoplasm divides to make 2 cells

15. Phases of Meiosis II Second division Just like mitosis
Prophase, Metaphase, Anaphase, Telophase
No chromosomes are replicated before starting meiosis II
Result of meiosis II: 4 genetically different haploid (n) cells formed
Become gametes (sex cells)

16. Mitosis Meiosis 2 4 identical different Diploid Diploid 2n  2n
Meiosis vs. Mitosis
Mitosis
Meiosis
Number of cells produced 2 4
Are cells produced genetically identical or different?
identical
different
Type of cells produced
Diploid Diploid
2n  2n
Somatic/body cells
Diploid  Haploid
2n  n
Sex cells
Type of reproduction
Asexual reproduction
Sexual reproduction
Number of divisions 1

17. Asexual Reproduction Involves one parent Binary fission
Replicates DNA and divides in half  cell splits into 2
Budding
Breaks off from parent and grows into new organism

18. Spore formation  fungi
Vegetative propagation
Making new plants from runners, stems, or roots
Regeneration
Making new organism from body parts

19. Sexual Reproduction
Union of 2 cells

20. Bell Ringer:
If a diploid cell containing 28 chromosomes undergoes meiosis, how many chromosomes will each daughter cell have?
In what process do male and female reproductive cells join during sexual reproduction?
a. segregation b. fertilization
c. self-pollination d. cross-pollination
3. What type of cell has 2 sets of chromosomes?
a. diploid b. haploid c. tetrad d. gene
4. There are four chromatids in a ___.
a. polygenic trait b. tetrad
c. gamete d. genotype