Reproduction & Development

LE 21-4 Animal development Gut Cell movement Zygote (fertilized egg) Eight cells Blastula (cross section) Gastrula (cross section) Adult animal (sea star) Cell division Morphogenesis Observable cell differentiation Plant development Seed leaves Shoot apical meristem Root apical meristem Zygote (fertilized egg) Two cells Embryo inside seed Plant

Differentiation Differences between cells come from gene expression, not differences in the cells’ genomes as regulatory mechanisms turn genes off and on

Reproductive Cloning of Mammals Dolly a lamb cloned from an adult sheep nuclear transplantation from a differentiated mammary cell premature death in 2003 arthritis speculation that her cells were “older” than those of a normal sheep

LE 21-7 Mammary cell donor Egg cell donor Egg cell from ovary Nucleus removed Cells fused Cultured mammary cells are semistarved, arresting the cell cycle and causing dedifferentiation Nucleus from mammary cell Grown in culture Early embryo Implanted in uterus of a third sheep Surrogate mother Embryonic development Lamb (“Dolly”) genetically identical to mammary cell donor

mice, cats, cows, horses, and pigs are now cloned “Copy Cat”

Problems Associated with Animal Cloning small percentage of cloned embryos have develop normally to birth

The Stem Cells of Animals Embryonic stem cells isolated from early embryos at the blastocyst stage Totipotent able to differentiate into all cell types Adult stem cells replace nonreproducing specialized cells Pluripotent able to give rise to multiple but not all cell types

LE 21-9 Embryonic stem cells Adult stem cells Totipotent cells Pluripotent cells Cultured stem cells Different culture conditions Different types of differentiated cells Liver cells Nerve cells Blood cells

Gene Expression During Development Tissue-specific proteins enable differentiated cells to carry out their specific tasks

LE 21-10_1 Nucleus Master control gene myoD Other muscle-specific genes DNA Embryonic precursor cell OFF OFF

LE 21-10_2 Nucleus Master control gene myoD Other muscle-specific genes DNA Embryonic precursor cell OFF OFF Determination mRNA OFF MyoD protein (transcription factor) Myoblast (determined)

LE 21-10_3 Nucleus Master control gene myoD Other muscle-specific genes DNA Embryonic precursor cell OFF OFF Determination mRNA OFF MyoD protein (transcription factor) Myoblast (determined) Differentiation mRNA mRNA mRNA mRNA Myosin, other muscle proteins, and cell-cycle blocking proteins MyoD Another transcription factor Muscle cell (fully differentiated)

Cell Signals in Cell Differentiation cytoplasmic determinants Maternal substances that influence early development regulate expression of genes that affect the cell’s developmental fate Induction signal molecules from embryonic cells cause transcriptional changes in nearby target cells

cytoplasmic determinant LE 21-11a Unfertilized egg cell Sperm Molecules of another cytoplasmic determinant Molecules of a cytoplasmic determinant Nucleus Fertilization Zygote (fertilized egg) Mitotic cell division Two-celled embryo Cytoplasmic determinants in the egg

Induction by nearby cells LE 21-11b Early embryo (32 cells) Signal transduction pathway NUCLEUS Signal receptor Signal molecule (inducer) Induction by nearby cells

Apoptosis programmed cell death

LE 21-19 Interdigital tissue 1 mm

Mechanisms of Plant Development Embryonic development Within the seed Meristems cell division, morphogenesis, and differentiation give rise to new organs i.e. apical meristems at the tips of shoots Site of height growth

Pattern Formation in Flowers floral meristem Participate in forming a flower carpels contain egg cells stamens contain sperm-bearing pollen Petals Sepals Leaflike structures outside the petals

LE 21-20 Carpel Stamen Petal L1 Cell layers L2 L3 Sepal Floral meristem Anatomy of a flower Tomato flower

LE 21-22 Wild type Mutant

Conservation of developmental genes LE 21-23 Adult fruit fly Fruit fly embryo (10 hours) Fly chromosome Mouse chromosomes Mouse embryo (12 days) Adult mouse

LE 21-24 Genital segments Thorax Abdomen Thorax Abdomen