1. Sexual Reproduction and Meiosis
Flowers I:
Sexual Reproduction and Meiosis

2. Sexual reproduction Fusion of two gametes to produce a zygote
Sperm and egg are male and female gametes
Sperm + Egg ---> Zygote
Zygote will develop into a new genetically unique individual
Introduces variation into a population, while offspring produced by asexual reproduction are genetic clones

3. Zygote and chromosomes
Zygote receives an equal number of chromosomes from each gamete
Gametes contain only one set of chromosomes - haploid
All other body cells contain two complete sets of chromosomes - diploid

4. Diploid Cells Two complete sets of chromosomes
Microscopically can see two of each kind of chromosome
Chromosome pairs are know as homologous chromosomes

5. Homologous chromosomes
Look alike and carry genes for the same traits
Each chromosome in a pair is derived from one of the haploid gametes
During fertilization the diploid number is restored in the zygote

6. Meiosis A specialized type of cell division
Occurs in all sexually reproducing organisms
Reduces the number of chromosomes from diploid to haploid
Without meiosis the number of chromosomes would double with each generation

7. Meiosis Consists of two consecutive divisions
Results in the formation of four haploid cells
Both divisions divided into four stages: prophase I prophase II
metaphase I metaphase II
anaphase I anaphase II
telophase I telophase II

8. Division I - Reduction Division
Prophase I similar to mitosis except that homologous chromosomes pair up (each member of pair composed of two chromatids)
Metaphase I - homologous chromosome pairs line across the cell
Anaphase I - homologous chromosomes separates
Telophase I - two daughter cells - each has half the number of chromosomes

9. Division II Prophase II - similar to mitosis except cells are haploid
Metaphase II - chromosomes line up
Anaphase II - chromatids separate
Telophase II - four haploid daughter cells from original diploid parent cell
The four cells have unique genetic combinations that differ from the parent cell

10. Meiosis In animals gametes are produced directly by meiosis
In plants gamete formation is delayed
In plants the products of meiosis are haploid cells called spores

11. Sporophytes and Gametophytes
Sporophyte is the diploid plant that undergoes meiosis to form spores
Spores develop into haploid plants called gametophytes that produce the gametes
In angiosperms, the gametophytes are always microscopic

12. Alternation of generations
Meiosis
Spores
Gametophyte
(haploid)
Sporophyte
(diploid)
Zygote
Gametes

13. Meiosis in flowering plants
Meiosis occurs in two parts of the flower
Stamens
in pollen chambers of anther
Carpels
in developing ovules in ovary

14. Flower Structure

15. Flowers

16. Flowers Sexual reproductive structure of angiosperms
Flower is a modified branch bearing four sets of floral organs
sepals
petals
stamens
carpels.
Floral organs inserted on the receptacle, expanded top of the pedicel or flower stalk

18. Sepals Leaf-like structures that cover the unopened flower bud
Usually green and photosynthetic
Whorl of sepals is called the calyx

19. Petals Often brightly colored and conspicuous
Function to attract animal pollinators
The whorls of petals called the corolla
Calyx and corolla comprise the perianth

20. Stamen Male reproductive structure
Pollen
chamber
Male reproductive structure
Consists of a pollen producing anther supported on a filament
Each anther has four pollen chambers
All stamens in a flower called androecium
Anther
Filament

21. Pollen chamber in anther

22. Carpels Flowers can have one to many carpels
Located in the middle of the flower
Gynoecium is collective term for all carpels

23. Carpels Stigma - expanded top of the carpel modified to trap pollen
Style - neck of the carpel
Ovary - expanded basal part with one to many ovules (structures which will eventually become seeds)

24. Carpels Simple pistil - a gynoecium with just one carpel
When multiple carpels are present:
May be fused together to form one compound pistil
May remain separate as many simple pistils

25. Simple and Compound Pistils
Orange
Green Bean

28. Monocots and dicots Monocots - floral parts in 3s or multiples of 3
Dicots - floral parts in 4s or 5s or multiples

29. Amaryllis a member of the Lily Family is a monocot.
There are 3 petals and 3 sepals, 6 stamens, and one carpel

30. Azalea, a dicot
Each flower has 5 sepals, 5 petals, 5 stamens, and one compound pistil composed of 5 carpels