BiologySylvia S. Mader

Michael Windelspecht

Chapter 42 Animal

Development and Aging

Lecture Outline

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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

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

Blastula

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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Neurulation

Organogenesis of Chick EmbryoRudimentary organs have formed (56 hours)

EyeForebrainHeart

Somites

Neural Tube

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

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

Stem Cells: Undifferentiated Cells

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

Major Stages of Embryogenesis

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

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

Determination & Differentiation

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

Apoptosis: programmed cell death

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?