Animal Development and Evolution

Principles of Animal Development


Fertilization

Sperm - head with acrosomal cap, midpiece, tail / Live 4-5 days
Egg - surrounded by extracellular matrix called the Zona Pellucida and Follicle Cells called the Corona Radiata
Fertilization

Sperm Cell membrane fuses with egg cell membrane
Egg nucleus and sperm nucleus unite - Zygote

Stages of Animal Development


Zygote
Early Cleavage Stages

Morula
Blastula

Gastrulation

Gastrula

Neurulation
Organogenisis

Cleavage - First mitotic divisions in a multicellular Zygote

Cell Divisions without growth in size
Continues until the Morula Stage



-Cleavage Stages
Morula Stage
Solid Balls of Cells

-Blastula Stage
Forms a hollow ball of cells with a fluid cavity (Blastocoel)

Gastrulation - invagination of cells into the Blastocoel

Form distant cell layers - ”Germ” layers
Pore Created - Blastopore
Cavity is called Archenteron - primitive gut / Inside of our digestive system

Early Gastrula - 2 tissue layers form

Ectoderm - outer layer of cells

Outer Body Tissues
Nervous System skin, teeth, eye and nails

Endoderm - Inner layer of cells

Inner body Tissues
Digestive systems and Glands

Late Gastrula - 3rd Tissue layer form

A middle Mesoderm layer is formed

Middle Body Tissues
Muscular/skeleton system and Cardio/respiratory/reproductive systems

Neurulation - Formation of the nervous system from the Ectoderm

Neural Folds form moving upward and joining to form a Neural Tube

Becomes the Brain and Spinal Cord

Organogenesis - Formation of the Organs

Common Traits in Vertebrates

Dorsal Neural Tube
Notochord
Pharyngeal gill pouches / Cause they look like gills
Postanal Tail

Human Embryonic and Fetal development

Overview

Human Development divided into 2 phases

Embryonic Phase - months 1-2
Fetal Development - months 3-9

Embryonic development - development of all organ systems

Week 1
Fertilization occurs within the 1/3 of the oviduct
Zygote undergoes the first cleavage divisions as it migrates through the oviduct toward the uterus
After about 3 days it is in the Morula stage
7 days to implantation
Week 2

Implantation occurs
Gastrulation occurs

Week 3

Organogenesis begins

Nervous systems develop
Cardiovascular development begins


Weeks 6-8

Becomes recognizable as human form
All organ systems are now established

Fetal Development - refinement of these systems

The Fetal period extends from the 3rd through 9th month
The 3rd and 4th months

Ossification of the skeleton begins / Hardening of the Bones
Sex of the individual may be determined
can hear the heartbeat during the 4th month


Enlargement of the Body systems and Fetus occurs until the 9th month (Birth)
Around the 8th month - Fetus sleeps 90-95% of the day, experiences REM Sleep, an indication of Dreaming

Birth

Contractions occur throughout pregnancy
Stage 1

Cervix begins to dilate
Water Breaks - Amnion ruptured pressure of baby’s head wedged into the Cervix
Stage 1 ends when the Cervix is fully dilated (10cm)

Stage 2

Contractions are 1-2 minutes apart and last about 1 minute
Urge to Push
Baby “Crowns”
Baby Emerges

Stage 3

Delivery of the Placenta
Occurs after the Birth of the Baby

Extraembryonic membranes

In Humans

Chorion develops into the fetal side of the Placenta

Gas and waste product exchange with maternal circulation

Allantois vessels become the umbilical vessels
Amnion contains the amniotic fluid / Has to break to start labor
Yolk Sac is the earliest site of blood cell formation

What was the thought before Darwin???


Lamarck (1801) - Came up with the idea of Inheritance of Acquired Characteristics
Which Says: The Subconscious ‘desires’ of an organism can cause changes in the traits of that organism
And those changes caused by increased use or disuse will be passed onto the offspring of that individual

Darwin

Studied medicine and Theology
was the naturalist on a 5 year voyage on the HMS Beagle. 1831
Wrote “The Origin of Species” 1859.

Darwin and Wallace

While Darwin was researching at his home he received a letter from Alfred Wallace
A young naturalist collecting organisms in South America
This letter was asking advice about an idea Wallace had been working on (Same as Darwin)
So we give Darwin the credit cause he did the most of the work and research (they authored together)

Evolution

Defined: Genetic change in Organisms over time through reproduction.


Main Points of Evolution

Populations evolve not individuals
Evolution mainly occurs through Natural Selection
Evolution is the main unifying theme of all biology

Example: Pepper Moth
Horse Evolution

Natural Selection

Variations in form of behavior between members of a species
These variations are inheritable from one generation to the next
There is competition between individuals of a population or species
Those individuals with the adaptable traits will be more likely to reproduce (differential reproduction success) and pass those adaptive traits on with greater frequency to future generations

Evidence of Evolution

Fossil Record
Artificial selection
Evolution in Action
Comparative Anatomy
Comparative Embryology
BioChemistry and DNA
Biogeography

Fossil Record

Evidence of past living organisms

What do they tell us?

Past organisms are different from todays living ones
Fossil layers show a trend in evolution from simple to more complex (generally)
Intermediate fossil are being found now.

Artificial Selection

Shows that change can occur and the environment can cause it
Many examples from our domestication of plants and animals

Evolution in action

Pesticide resistance in insects
Bacterial and Viral resistance to Medicine

Comparative Anatomy

comparing the structure of organisms to see if the individuals are related or not

3 Types of Structures

Homologous - Structures that have the same framework (Internal Structure)
Analogous - Structures that dont have the same framework
Vestigial - Structures that have no apparent use in the present owner but are used in related organisms

Similar Vertebrates Embryos

Genes past through common ancestry

Biochemistry and DNA

Shows which Organisms are related to each other
How???
DNA and its gene sequence comparison between Humans and Chimps
Red Panda and Giant Panda = Panda is a Bear

BioGeography

What is it??? Study of life on the planet / Marsupials are in Australia because they are isolated by Geography the placental animals survuved better as the land was notr separated as they better adapted before the split.
Example: large flightless birds descended from a common ancestor, regardless of were they live.
Also deals with Plate Tectonics and Continental Drift. Comes from Geology

Continental Drift

Idea that the continents were once joined and have since drifted apart. (moves 1-2 inches a year)
Due to plate tectonics

Plate Tectonics

Earths crust is fractured into plates
Movement of Plates is driven by upwelling of molten Rock at mid-oceanic ridges
As seafloor spreads, older rock is forced down into trenches

Summary of Darwin’s Theory

Individuals in nature differ from one another
Organisms in nature produce more offspring that can survuve, and many of those who do not reproduce
Because more organisms are produced than can survive, each species must struggle for resources
Each Organism is unique, each has advantages and disadvantages in the struggle for existence
Individuals best suited for the environment survive and reproduce most successful
Species change over time (to survive)

MicroEvolution

Small scale genetic changes in populations
Causes of Microevolution

Mutation
Gene Flow
Genetic Drift
Natural Selection

Mutations - Changes ini the DNA that are passed onto the Offspring
(1in a million gametes a mutation occurs)

Types of Mutations

Lethal Mutation
Adaptive Mutation
Neutral Mutation (most common occurring mutation)

Gene Flow - The exchange of genes between populations

Making populations similar in traits and genetics

Genetic Drift - The random genetic changes in a population

Sub Types -

Founder Effects -

When a small group of individuals colonize a new habitat and thrive, becoming a new population (Common on Islands)

Bottleneck Effects -

When there is a sever reduction in population size, the resulting population will have less genetic variation and more similar traits (Cheetahs have gone thru 2 Bottleneck effects/They are too similar; sterile)

Natural Selection -

Types of Natural Selection

Stabilizing Selection

Intermediate forms are favored and extremes are eliminated

Directional Selection

Allele frequencies shift in one direction (Pepper Moth Example)

Disruptive Selection

Allele frequencies shift in two directions!

Special Population Selection Models

Sexual Selection - When one form or sex chooses its mate based on fitness of that individual. (Chooses the best mate)

Causes a huge amount of genetic change within 1 generation of a population.
Requires Sexual Dimorphism

a species with 2 forms of sex

Occurs only during the mating season

Genetic (balanced) polymorphism - When there are two forms of a trait that are maintained within a population year after year

Example -
Sickle Cell Trait: Heterozygote Advantage

Sickle Cell is more resistant to Malaria, so it stays around because of the advantage to the population of people who live in Africa (Can only have this through Genetics) Get Malaria from the Female Mosquito only

Macroevolution

Large Scale genetic change or evolution
Development of new species

What is a species - A group of interbreeding individuals that are reproductively isolated form other such groups (Genetically Distinct) (Cant Breed Together)

Reproductive isolation

A PreZygotic isolation (Before Sperm and Egg Meet)

Behavioral R.I. - The mating behavior between species keep them from reproducing (King Cobra - mating behaviors - sniff,touch tongues, dance the other and snakes have to rub up against each other to excite to mate 4 ft off the ground)
Ecological R.I. - They live in different habitats
Temporal R.I. - The mating seasons are different
Mechanical R.I. - The reproductive parts don’t fit
Gametic R.I. - The sperm does not survive in the females environment

PostZygotic Isolation

Zygotic R.I. The embryo dies before birth
Hybrid inviability - The offspring does not survive well and dies before reproductive age
Hybrid Sterility - The offspring is sterile and can’t pass on the new genetics (Like a Mule - Female Horse and a Male Donkey can only produce this)

Hybrids (Horse and Zebra)

Zorses! (It can produce on its own / New Species) Wacky things happen on Farms changes the mating rituals of each species

Speciation & Natural Selection

Natural Selection can lead to speciation
Speciation - can also occur as a result of other microevolutionary processes

Genetic Drift
Mutation
Etc...

Speciation Models

Allopatric Speciation - The development of new species by a physical separation from the original species (Oceans, Mountains, etc.)

Sympatric Speciation - The development of a new species within the same environment as the original species

Rates of Speciation

Gradualism - at a slow and gradual rate
Punctuated Equilibrium - The development of new species in a short amount of time, then those species remain the same

(SubType - Adaptive Radiation) - is the new development of ALOT of new species at one time. (Has happened 7 times on the planet, always after 85% extinction of organisms)

Extinctions

3 types

Local Extinctions - a part of species in a specific area
Species Extinction - Entire Species is Gone forever (Cheetahs are next for Example)
Mass Extinctions

have played a major role in evolutionary history (Are in the middle of the 7th now) The 6th one was the (Ice Age)