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BiologySylvia S. Mader
Michael Windelspecht
Chapter 42 Animal
Development and Aging
Lecture Outline
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See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into
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Fertilization
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corona radiata
zona pellucida
oocyte plasma membrane
egg pronucleus
cortical granule
fertilization membrane
tail
headacrosome
sperm pronucleus
microvilli of oocyte plasma membrane
sperm
1. Sperm makes its way through the corona radiata.
2. Acrosomal enzymes digest a portion of zona pellucida.
3. Sperm binds to and fuses with oocyte plasma membrane.
4. Sperm nucleus enters cytoplasm of oocyte.
5. Cortical granules release enzymes; zona pellucida becomes fertilization membrane.
6. Sperm and egg pronuclei are enclosed in a nuclear envelope.
© David M. Phillips/Visuals Unlimited; (Chick, p. 779): © Photodisc/Getty Images
middlepiece
plasmamembranenucleus
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Early Developmental Stages
Development – all changes that occur during the life cycle
First stages of development, organism is called an embryo
After fertilization, the zygote undergoes cleavage• Cleavage is cell division without growth
• Morula forms a blastula with a hollow blastocoel
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CleavageNote: Size is not increasing
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Tissue Development
Gastrulation – formation of a gastrula
• Germ layer formation and differentiation
• Blastopore – Pore created by the
inward folding of cells
– Eventually becomes the anus
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Embryonic Germ Layers
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Organ Development
• Formation of organs
• 1st to develop Neural tube Notochord Skeletal rod
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Organogenesis of Chick EmbryoRudimentary organs have formed (56 hours)
EyeForebrainHeart
Somites
Neural Tube
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Extraembryonic Membranes
Chorion –Gas exchange
Amnion –Fluid filled
Allantois – collects nitrogenous wastes (umbilical cord)
Yolk sac – provides nourishment
Presence of embryonic membranes in humans demonstrates our evolutionary relationship to reptiles
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Extraembryonic Membranes
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chorion
Human
Chick
amnion
embryoallantois
yolk sac
chorion
amnion
yolk sac
embryo
allantois
maternal portionof placenta
fetal portionof placenta
umbilicalcord
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Placenta
• Mammalian structure that functions in gas, nutrient, and waste exchange between embryonic &maternal cardiovascular systems.
• Begins formation once the embryo is fully planted
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Three Stages of Parturition
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rupturedamnioticsac
a. First stage of birth: cervix dilates
placenta
b. Second stage of birth: baby emerges
placenta
uterus
umbilicalcord
c. Third stage of birth: expelling afterbirth
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Stem Cells: Undifferentiated Cells
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42.2 Developmental Processes
• Development requires: Growth Cellular Differentiation
• Cells become specialized in structure and function
Morphogenesis• Produces the shape and form of the body• Includes pattern formation
– Arrangement of tissues and organs within the body– Involves apoptosis
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Morphogenesis & Changes in Cell Shape
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Major Stages of Embryogenesis
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Developmental Processes
• Cellular Differentiation The zygote is totipotent
• Cellular Differentiation (continued) Cytoplasmic Segregation
• Maternal determinants are parceled out during mitosis
• Cytoplasm of a frog’s egg is not uniform
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Cytoplasmic Segregation
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Cytoplasmic segregation
maternal determinants
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InductionThe ability of one embryonic tissue to influence the development of another tissue
Molecular concentration gradients may act as chemical signals to induce germ layer differentiation
Developmental path of cells is influenced by neighboring cells
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Cytoplasmic Influence on Development
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animal poleDorsal
Posterior
vegetal pole
Dorsal
Anterior
Anterior
Ventral Posterior
a. Zygote of a frog is polar and has axes.
plane offirst division
graycrescent
site ofspermfusion
b. Each cell receives a part of the gray crescent
c. Only the cell on the left receives the gray crescent
Ventral
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Determination & Differentiation
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Pattern Formation in Drosophila
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fly chromosome
Hox-2
Hox-1
Hox-3
Hox-4
fruit fly
fruit fly embryo
mouse
a.
b.
mousechromosomes
mouseembryo
Courtesy E.B. Lewis
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Apoptosis: programmed cell death
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Developmental Processes
• Homeotic Genes control pattern formation Organization of differentiated cells into specific
three-dimensional structures In Drosophila, certain genes control whether a
particular segment will bear antennae, legs, or wings
• Homeotic genes all contain the same particular sequence of nucleotides, the homeobox, that encodes a 60-amino-acid sequence called a homeodomain
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How does this happen?