Aim how do zygotes develop
This presentation is the property of its rightful owner.
Sponsored Links
1 / 39

Aim: How do zygotes develop? PowerPoint PPT Presentation


  • 57 Views
  • Uploaded on
  • Presentation posted in: General

Aim: How do zygotes develop?. 0. Comparing Genomes Within a Species. As a species, humans have only been around about 200,000 years and have low within-species genetic variation Most of the variation within humans is due to single nucleotide polymorphisms ( SNPs )

Download Presentation

Aim: How do zygotes develop?

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Aim how do zygotes develop

Aim: How do zygotes develop?

0


Comparing genomes within a species

Comparing Genomes Within a Species

As a species, humans have only been around about 200,000 years and have low within-species genetic variation

Most of the variation within humans is due to single nucleotide polymorphisms (SNPs)

There are also inversions, deletions, and duplications and a large number of copy-number variants (CNVs)

These variations are useful for studying human evolution and human health


Fertilization cleavage and gastrulation initiate embryonic development

Fertilization, cleavage, and gastrulation initiate embryonic development

Across animal species, embryonic development involves common stages occurring in a set order

First is fertilization, which forms a zygote

During the cleavage stage, a series of mitoses divide the zygote into a many-celled embryo

The resulting blastula then undergoes rearrangements into a three-layered embryo called a gastrula


Figure 36 14

Figure 36.14

EMBRYONIC DEVELOPMENT

Sperm

Zygote

Adult

frog

Egg

FERTILIZATION

CLEAVAGE

Blastula

Metamorphosis

GASTRULATION

ORGANO-GENESIS

Larval

stages

Gastrula

Tail-bud

embryo


Figure 35 15 5

Figure 35.15-5

Sperm plasma

membrane

Sperm

nucleus

Acrosomal

process

Basal body

(centriole)

Actin

filament

Sperm

head

Cortical

granule

Fused

plasma

membranes

Perivitelline

space

Acrosome

Hydrolytic enzymes

Jelly coat

Fertilization

envelope

Vitelline layer

Sperm-

binding

receptors

Egg plasma membrane


Cleavage and gastrulation

Cleavage and Gastrulation

Fertilization is followed by cleavage, a period of rapid cell division without growth

Cleavage partitions the cytoplasm of one large cell into many smaller cells

The blastula is a ball of cells with a fluid-filled cavity called a blastocoel

The blastula is produced after about five to seven cleavage divisions


Figure 36 17

Figure 36.17

50 m

(a) Fertilized egg

(b) Four-cell stage

(c) Early blastula

(d) Later blastula


Aim how do zygotes develop

After cleavage, the rate of cell division slows

The remaining stages of embryonic development are responsible for morphogenesis, the cellular and tissue-based processes by which the animal body takes shape


Aim how do zygotes develop

During gastrulation, a set of cells at or near the surface of the blastula moves to an interior location, cell layers are established, and a primitive digestive tube forms

The hollow blastula is reorganized into a two- or three-layered embryo called a gastrula


Aim how do zygotes develop

The cell layers produced by gastrulation are called germ layers

The ectoderm forms the outer layer and the endoderm the inner layer

In vertebrates and other animals with bilateral symmetry, a third germ layer, the mesoderm, forms between the endoderm and ectoderm


Figure 36 18

Figure 36.18

Animal

pole

Blastocoel

Mesenchyme cells

Vegetal plate

Vegetal

pole

Blastocoel

Filopodia

Archenteron

Mesenchyme cells

Blastopore

50 m

Key

Blastocoel

Future ectoderm

Ectoderm

Future mesoderm

Archenteron

Future endoderm

Mouth

Blastopore

Mesenchyme

(mesoderm forms

future skeleton)

Digestive tube (endoderm)

Anus (from blastopore)


Figure 36 19

Figure 36.19

ECTODERM (outer layer of embryo)

  • Epidermis of skin and its derivatives (including sweat glands,

  • hair follicles)

  • Nervous and sensory systems

  • Pituitary gland, adrenal medulla

  • Jaws and teeth

  • Germ cells

MESODERM (middle layer of embryo)

  • Skeletal and muscular systems

  • Circulatory and lymphatic systems

  • Excretory and reproductive systems (except germ cells)

  • Dermis of skin

  • Adrenal cortex

ENDODERM (inner layer of embryo)

  • Epithelial lining of digestive tract and associated organs

  • (liver, pancreas)

  • Epithelial lining of respiratory, excretory, and reproductive tracts

  • and ducts

  • Thymus, thyroid, and parathyroid glands


Aim how do zygotes develop

A program of differential gene expression leads to the different cell types in a multicellular organism

A fertilized egg gives rise to many different cell types

Cell types are organized successively into tissues, organs, organ systems, and the whole organism

Gene expression orchestrates the developmental programs of animals


Aim how do zygotes develop

Cell differentiation is the process by which cells become specialized in structure and function

The physical processes that give an organism its shape constitute morphogenesis

Differential gene expression results from genes being regulated differently in each cell type

Materials in the egg can set up gene regulation that is carried out as cells divide


Cytoplasmic determinants and inductive signals

Cytoplasmic Determinants and Inductive Signals

An egg’s cytoplasm contains RNA, proteins, and other substances that are distributed unevenly in the unfertilized egg

Cytoplasmic determinants are maternal substances in the egg that influence early development

As the zygote divides by mitosis, the resulting cells contain different cytoplasmic determinants, which lead to different gene expression


Aim how do zygotes develop

The other major source of developmental information is the environment around the cell, especially signals from nearby embryonic cells

In the process called induction, signal molecules from embryonic cells cause transcriptional changes in nearby target cells

Thus, interactions between cells induce differentiation of specialized cell types


Sequential regulation of gene expression during cellular differentiation

Sequential Regulation of Gene Expression During Cellular Differentiation

Determination commits a cell irreversibly to its final fate

Determination precedes differentiation


Apoptosis a type of programmed cell death

Apoptosis: A Type of Programmed Cell Death

While most cells are differentiating in a developing organism, some are genetically programmed to die

Apoptosis is the best-understood type of “programmed cell death”

Apoptosis also occurs in the mature organism in cells that are infected, damaged, or at the end of their functional lives


Aim how do zygotes develop

During apoptosis, DNA is broken up and organelles and other cytoplasmic components are fragmented

The cell becomes multilobed and its contents are packaged up in vesicles

These vesicles are then engulfed by scavenger cells

Apoptosis protects neighboring cells from damage by nearby dying cells


Aim how do zygotes develop

Apoptosis is essential to development and maintenance in all animals

It is known to occur also in fungi and yeasts

In vertebrates, apoptosis is essential for normal nervous system development and morphogenesis of hands and feet (or paws)


Figure 16 6

Figure 16.6

1 mm

Interdigital tissue

Cells undergoing apoptosis

Space between digits


Pattern formation setting up the body plan

Pattern Formation: Setting Up the Body Plan

Pattern formation is the development of a spatial organization of tissues and organs

In animals, pattern formation begins with the establishment of the major axes

Positional information, the molecular cues that control pattern formation, tells a cell its location relative to the body axes and to neighboring cells


Aim how do zygotes develop

Pattern formation has been extensively studied in the fruit fly Drosophila melanogaster

Combining anatomical, genetic, and biochemical approaches, researchers have discovered developmental principles common to many other species, including humans


Figure 16 7

Figure 16.7

1

2

3

4

5

Thorax

Head

Abdomen

Follicle cell

Egg

developing within

ovarian follicle

Nucleus

Egg

0.5 mm

Nurse cell

Dorsal

Right

Egg

shell

Unfertilized egg

BODY

AXES

Posterior

Anterior

Depleted

nurse cells

Left

Ventral

Fertilization

Laying of egg

(a) Adult

Fertilized egg

Embryonic

development

Segmented

embryo

0.1 mm

Body

segments

Hatching

Larval stage

(b) Development from egg to larva


Aim how do zygotes develop

The Drosophila eggs develop in the female’s ovary, surrounded by ovarian cells called nurse cells and follicle cells

After fertilization, embryonic development results in a segmented larva, which goes through three stages

Eventually the larva forms a cocoon within which it metamorphoses into an adult fly


Genetic analysis of early development scientific inquiry

Genetic Analysis of Early Development: Scientific Inquiry

Edward B. Lewis, Christiane Nüsslein-Volhard, and Eric Wieschaus won a Nobel Prize in 1995 for decoding pattern formation in Drosophila

Lewis discovered the homeotic genes, which control pattern formation in late embryo, larva, and adult stages


Figure 16 8

Figure 16.8

Wild type

Mutant

Eye

Leg

Antenna


Axis establishment

Axis Establishment

Maternal effect genes encode cytoplasmic determinants that initially establish the axes of the body of Drosophila

These maternal effect genes are also called egg-polarity genes because they control orientation of the egg and consequently the fly


Aim how do zygotes develop

One maternal effect gene, the bicoid gene, affects the front half of the body

An embryo whose mother has no functional bicoid gene lacks the front half of its body and has duplicate posterior structures at both ends

Bicoid: A Morphogen Determining Head

Structures


Figure 16 9

Figure 16.9

Head

Tail

A8

T2

T1

A7

T3

A6

A5

A1

A2

A4

A3

Wild-type larva

250 m

Tail

Tail

A8

A8

A7

A7

A6

Mutant larva (bicoid)


Aim how do zygotes develop

This phenotype suggested that the product of the mother’sbicoid gene is concentrated at the future anterior end and is required for setting up the anterior end of the fly

This hypothesis is an example of the morphogen gradient hypothesis; gradients of substances called morphogens establish an embryo’s axes and other features


Aim how do zygotes develop

The bicoid mRNA is highly concentrated at the anterior end of the embryo

After the egg is fertilized, the mRNA is translated into Bicoid protein, which diffuses from the anterior end

The result is a gradient of Bicoid protein

Injection of bicoid mRNA into various regions of an embryo results in the formation of anterior structures at the site of injection


Comparing developmental processes

Comparing Developmental Processes

Evolutionary developmental biology, or evo-devo, compares the developmental processes of different multicellular organisms

Genomic information shows that minor differences in gene sequence or regulation can result in striking differences in form


Widespread conservation of developmental genes among animals

Widespread Conservation of Developmental Genes Among Animals

Molecular analysis of the homeotic genes in Drosophila has shown that they all include a sequence called a homeobox

An identical or very similar nucleotide sequence has been discovered in the homeotic genes of both vertebrates and invertebrates

The vertebrate genes homologous to homeotic genes of flies have kept the same chromosomal arrangement


Figure 18 17

Figure 18.17

Adult

fruit fly

Fruit fly embryo

(10 hours)

Fly

chromosome

Mouse

chromosomes

Mouse embryo

(12 days)

Adult mouse


Aim how do zygotes develop

Related homeobox sequences have been found in regulatory genes of yeasts and plants

The homeodomain is the part of the protein that binds to DNA when the protein functions as a transcriptional regulator

The more variable domains in the protein recognize particular DNA sequences and specify which genes are regulated by the protein


Aim how do zygotes develop

Sometimes small changes in regulatory sequences of certain genes lead to major changes in body form

For example, variation in Hox gene expression controls variation in leg-bearing segments of crustaceans and insects


Figure 18 18

Figure 18.18

Genital

segments

Thorax

Abdomen

Thorax

Abdomen


Figure 18 un01a

Figure 18.UN01a


  • Login