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Flowers I:

Explore the intricate process of meiosis in sexual reproduction, from zygote formation to genetic variation. Learn the stages of meiosis, chromosome dynamics, and the role of gametes. Discover how flowering plants undergo meiosis in flower structures like stamens and carpels.

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Flowers I:

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  1. 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

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

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

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

  20. Pollen chamber in anther

  21. Carpels • Flowers can have one to many carpels • Located in the middle of the flower • Gynoeciumis collective term for all carpels

  22. 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)

  23. Carpels • Simplepistil- a gynoecium with just one carpel • When multiple carpels are present: • May be fused together to form one compoundpistil • May remain separate as many simple pistils

  24. Simple and Compound Pistils Orange Green Bean

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

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

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

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