Reproduction

1
Reproduction Development
2
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
Seed leaves
Plant development
Shoot apical meristem
Root apical meristem
Two cells
Zygote (fertilized egg)
Embryo inside seed
Plant
3
Differentiation

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

4
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

5
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
6

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

7
Problems Associated with Animal Cloning

• small percentage of cloned embryos have develop
  normally to birth

8
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

9
LE 21-9
Embryonic stem cells
Adult stem cells
Pluripotent cells
Totipotent cells
Cultured stem cells
Different culture conditions
Different types of differentiated cells
Liver cells
Nerve cells
Blood cells
10
Gene Expression During Development

• Tissue-specific proteins
• enable differentiated cells to carry out their
  specific tasks

11
LE 21-10_1
Nucleus
Master control gene myoD
Other muscle-specific genes
DNA
Embryonic precursor cell
OFF
OFF
12
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)
13
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)
14
Cell Signals in Cell Differentiation

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

15
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
16
LE 21-11b
Early embryo (32 cells)
Signal transduction pathway
NUCLEUS
Signal receptor
Signal molecule (inducer)
Induction by nearby cells
17
Apoptosis

• programmed cell death

18
LE 21-19
Interdigital tissue
1 mm
19
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

20
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

21
LE 21-20
Carpel
Petal
Stamen
L1
Cell layers
L2
L3
Sepal
Floral meristem
Anatomy of a flower
Tomato flower
22
LE 21-22
Wild type
Mutant
23
LE 21-23
Conservation of developmental genes
Adult fruit fly
Fruit fly embryo (10 hours)
Fly chromosome
Mouse chromosomes
Mouse embryo (12 days)
Adult mouse
24
LE 21-24
Genital segments
Thorax
Abdomen
Thorax
Abdomen