General Biology II: Development I & II

Development

These are all changes that occur during a lifetime

Plasma membrane & outer coverings

What does the egg have?

For gametic isolation and prevention of polyspermy

Why does the egg need to screen the sperm?

Fertilization

n + n = 2n which can restore 2n number, determines sex and activate the egg

1) Sperm touches the egg (receptors)

2) This leads to an acrosomal reaction → sperm contact with zona pellucida and binding with the protein ZP3 and acrosome dissolves egg outer layer

3) Plasmogamy → Leads to Calcium wave (increase in Ca²⁺) then a cortical reaction

4) Enzyme will catalyze changes in ZP, where no more sperm can enter

5) Egg activation, oogenesis completes with 2nd polar body and egg and karyogamy happens

SEQ fertilization

1) Sperm touches the egg (receptors)

1st step of fertilization

2) This leads to an acrosomal reaction → sperm contact with zona pellucida and binding with the protein ZP3 and acrosome dissolves egg outer layer

2nd step fertilization

3) Plasmogamy → Leads to Calcium wave (increase in Ca²⁺) then a cortical reaction

3rd step of fertilization

4) Enzyme will catalyze changes in ZP, where no more sperm can enter

4th step of fertilization

5) Egg activation, oogenesis completes with 2nd polar body and egg and karyogamy happens

5th step of fertilization

Cleavage

When single cell zygote becomes an embryo which is characterized by rapid mitosis, short or no G1 or G2 phases with no cell growth (cell division)

Zygote → Embryo → Blastua → Cleavage

How to get to cleavage?

Cleavage Furrow

This is the indentation during cytokinesis

Animal Pole

This is also known as an embryo

Vegetal Pole

This is also known as a yolk

Equal Holoblastic

Cleavage furrow will pass entirely through egg (egg equator) with an equal division of egg cytoplasm (equal blastomeres) and occurs with small yolk → sea urchins/humans

Unequal Holoblastic

Cleavage furrow passes entirely through egg (side of egg) with unequal division of egg cytoplasm → unequal blastomeres where it occurs with some yolk (frogs)

Meroblastic

Cleavage furrow does not pass entirely through egg (a zygote) which only occurs only in animal pole with LARGE YOLK → Birds/other reptiles/fish

Gastrulation/Gastrula

Layered embryo with 3 embryotic germ layers (ectoderm, endoderm, mesoderm)

Sea Urchin Gastrulation

These are radially symmetrical, holoblastic, and have invagination

Invagination

Folding in on itself

Archenteron

Primitive gut

1) Cells at vegetal pole - migrate to blastocoel

2) Cells at vegetal pole flatten - causing invagination

3) Endoderm cells form archenteron

4) Archenteron dragged through to opposite side

5) Archenteron fuses with blastocoel wall

SEQ Sea urchin Gastrulation

1) Cells at vegetal pole - migrate to blastocoel

1st step of sea urchin gastrulation

2) Cells at vegetal pole flatten - causing invagination

2nd step of sea urchin gastrulation

3) Endoderm cells form archenteron

3rd step of Sea Urchin gastrulation

4) Archenteron dragged through to opposite side

4th step of Sea Urchin gastrulation

5) Archenteron fuses with blastocoel wall

5th step of Sea Urchin gastrulation

Chicken gastrulation

This is all about the yolk where the embryo initially forms 2 layers (epiblast and hypoblast) where they eventually form the primitive steak

1) Embryo forms 2 layers → epiblast and hypoblast

2) Epiblast might migrate to midline producing the primitive steak (invagination for 3 germ layers)

SEQ Chicken Gastrulation

Epiblast

Will help form the embryo (3 germ layers) in chicken gastrulation

Hypoblast

A sac around the embryo in chicken gastrulation (helps form the yolk??)

Primitive Steak

This is formed during gastrulation in chickens

Human Gastrulation

These contain trophoblasts, inner cell mass, blastomere, etc.

Blastomere

These cells are formed during cleavage in human gastrulation

Trophoblast

Outer single later of cells that secrete enzymes which will erode area of endometrium during implantation and becomes support tissue (placenta) Acts as your connection between embryo and uterus

Inner Cell Mass

This will become the embryo (blastocyst) and some support tissue in human gastrulation

Blastocoel

becomes nothing

Implantation

Trophoblast thickens and extends fingerlike projections into endometrium

Epiblast

Embryo (will become endo, ecto, meso) in human gastrulation

Hypoblast

Extraembryonic membranes - amnion (will become extraembryonic membranes); becomes amniotic sac in human gastrulation

Blastocyst

Will become blastocoel in Human gastrulation

Amnion

Bag of waters in amniotic sac →human gastrulation

Yolk Sac

Forms blood cells in human gastrulation

Allantois

Blood vessels and umbilical cord in human gastrulation

Organogenesis

When rate of mitosis begins to slow down and new organs are formed

slows down

What happens to the rate of mitosis following cleavage?

Morphogenesis

Forms cells & tissues and animal body which occurs during gastrulation and organogenesis

Neurulation

Nerve cell formation

Nervous System

What system is developed first in vertebrates?

Notochord

This is developed in the mesoderm which induces/forms neural plate (forms neural tube)

Induction

Certain cells influence/stimulate neighboring cells (paracrine signaling)

Neural Plate

This will roll up and form a neural tube (the CNS) anterior is brain and remainder is spinal cord

Anencephaly

Anterior, no forebrain (a malformation in neurulation)

Spina Bifida

Posterior and the folic acid (malformation)

Cell Migration

Local cellular interactions/activities where some can be long range

Neural Crest

Some will migrate to form nerves, teeth, skull bones

Somites

Blocks of cells in mesoderm, lateral to notochord contribute to repeating structures → Vertebrae, no cage, skeletal muscle, tendons and more

1) hCG released by anterior pituitary and acts like LH on corpus luteum to progestrone and estrogens

2) Nutrients for embyro come from the endometrium

3) Trophoblast will partially form placenta

4) When placenta fully formed, it will do its job

5) Labor??

SEQ human development

Placenta

Gas exchange and nutrients where blood is not mixing waste

1) hCG released by anterior pituitary and acts like LH on corpus luteum to progestrone and estrogens

1st step towards human development

2) Nutrients for embyro come from the endometrium

2nd step towards human development

3) Trophoblast will partially form placenta

3rd step towards human development

4) When placenta fully formed, it will do its job

4th step towards human development

5) Labor??

5th step towards human development

Identical twins

One egg and one sperm where cells will split in first month

Fraternal twins

2 eggs and 2 sperm form this

1) Childbirth begins with labor

2) 266 days from time of fertilization

3) Dilation, birth, delivery of afterbirth

4) Postpartum

5) Postnatal care

6) Lactation for mammals

SEQ Birth

1) Childbirth begins with labor

1st step of birth

2) 266 days from time of fertilization

2nd step of birth

3) Dilation, birth, delivery of afterbirth

3rd step of birth

4) Postpartum

4th step of birth

5) Postnatal care

5th step of birth

6) Mammal lactation

6th step for birth

1) Cleavage in oviduct → blastomeres formed

2) Inner Cell mass forms (epiblast & Hypoblast)

3) Implantation where trophoblast thickens and secretes enzymes to erode an area of endometrium for it to become placenta

4) Epiblast will become embryo & Hypoblast becomes amnion

SEQ Human Gastrulation

1) Cleavage in oviduct → blastomeres formed

1st step of human gastrulation

2) Inner Cell mass forms (epiblast & Hypoblast)

2nd step of human gastrulation

3) Implantation where trophoblast thickens and secretes enzymes to erode an area of endometrium for it to become placenta

3rd step of human gastrulation

4) Epiblast will become embryo & Hypoblast becomes amnion

4th step of human gastrulation