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Flowers I:

Flowers I:. Sexual Reproduction and Meiosis. 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

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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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