The Cellular Basis of Inheritance: Life Cycles Chapters 7 and 14

Life Cycles Fertilization and meiosis alternate in sexual life cycles Meiosis reduces the chromosome number by half Producing haploid cells Fertilization, the joining of two gametes, restores the chromosome number Producing diploid cells

Animal Kingdom Life Cycle Animals use Gametic Meiosis Diploid-dominant Meiosis produces haploid gametes Gametes do not divide (remain uni- cellular) Fertilization produces a diploid zygote Zygote undergoes mitosis to produce a multicellular diploid body (adult animal)

Fungus Kingdom Life Cycle Fungus use Zygotic Meiosis Haploid-dominant Meiosis of the zygote produces haploid spores Spores undergo mitosis to produce a multicellular haploid body (mycelium/fungus) Mycelia of two fungi fuse and develop into a fruiting body (mushroom) Fertilization produces a diploid zygote Zygote remains uni-cellular Zygote is the only diploid cell during the life cycle

a g mycelium Diploid Zygote Diploid Stage nuclear fusion meiosis Haploid Stage Cells with two nuclei (n + n) form on gills g spore (n) at gill margin gill Mitosis cap stalk mycelium cytoplasmic fusion mycelium

Plant Kingdom Life Cycle Plants use Sporic Meiosis alternation of generations Meiosis produces haploid spores Spores undergo mitosis to produce a multicellular haploid body (gametophyte) Fertilization produces a diploid zygote Zygote undergoes mitosis to produce a multicellular diploid body (sporophyte) Alternates between multi-cellular diploid and multi-cellular haploid bodies

multicelled sporophyte mitosis Meiosis Haploid (n) Phase of Cycle spores zygote Diploid (2n) Phase of Cycle Fertilization gametes mitosis Figure 21.3 Generalized plant life cycle. multicelled gametophyte mitosis Stepped Art Fig, 21.3, p. 326

Plant Kingdom Life Cycle Sporophyte (diploid, multicellular) Produces flowers which contain the germ cells Germ cells are located in the carpel (ova) and stamen (pollen)

Plant Kingdom Life Cycle Production of the ova Occurs in flowers within the pistil Made up of 1 or more carpels Stigma Style Ovary

Plant Kingdom Life Cycle Production of the ova Occurs in flowers within the pistil The ovary contains 1 or more ovules which produce egg sacs Meiosis of the ovules produces spores Spores undergo mitosis to become the egg sac (gametophyte) Meiosis Spores Egg Sac Mitosis

an ovule ovary wall megasporocyte integument stalk ovary (cutaway view) Diploid Stage Haploid Stage Double Fertilization Meiosis

Plant Kingdom Life Cycle Production of pollen Occurs in flowers in the stamen Anther Filament

Plant Kingdom Life Cycle Production of pollen The anther contains germ cells in pollen sacks Meiosis produces spores Spores undergo mitosis to become the pollen (gametophyte)

Plant Kingdom Life Cycle Pollination The transfer of pollen from an anther to a stigma (not fertilization) Wind, insects, mammals, etc. Released pollen lands on the stigma Pollen grows a tube through the style to the ovary

Plant Kingdom Life Cycle Fertilization Two sperm enter the egg sac from the pollen tube One fuses with the egg forming the diploid zygote Develops into the embryo The other fuses with the central cell to form a triploid endosperm

Plant Kingdom Life Cycle Development A seed develops from each mature fertilized ovule Fruit develops from the ovary or other tissue Embryo grows into a new mature sporophyte Nutritive tissue Embryo Seed Ovule Ovary

Fig. 27-5, p.451