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BY1101 Introduction to Molecular and Cellular Biology . Tutorial for module BY1101: Embryology Joe Colgan ([email protected]). BY1101 Introduction to Molecular and Cellular Biology . Tutorial objectives. Describe the main events in embryogenesis

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BY1101 Introduction to Molecular and Cellular Biology

Tutorial for module BY1101:

Embryology

Joe Colgan ([email protected])

tutorial objectives

BY1101 Introduction to Molecular and Cellular Biology

Tutorial objectives
  • Describe the main events in embryogenesis
  • Compare and contrast the events between different organisms
embryology

BY1101 Introduction to Molecular and Cellular Biology

Embryology

What is embryology?

-The science of the development of an organism from the fertilisation of the ovum to the fetus

sexual reproduction

BY1101 Introduction to Molecular and Cellular Biology

Sexual reproduction

What are gametes?

Haploid germ cells (sperm or egg (ovum))

What is a zygote?

Single diploid cell (earliest stage of embryonic development)

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BY1101 Introduction to Molecular and Cellular Biology

How do the gametes form?

Mitosis:

Process of nuclear division in eukaryotic cells

Conserves chromosome number by allocating replicated chromosomes equally to each of the daughter nuclei

Meiosis:

Modified form of cell division in sexually reproducing organisms

Involves two round of cell division but only one round of DNA replication

Produces cells with half the numbers of chromosome sets as the original cell

what differences are there in the ga metes

BY1101 Introduction to Molecular and Cellular Biology

What differences are there in the gametes?

Oogenesis

Product:

Ovum (Egg)

Location:

Ovary

Specialised function:

Nutrition, metabolism and development

Spermatogenesis

Product:

Sperm

Location:

Testes (Seminiforous tubule)

Specialised function:

Location and penetration

stage 1 gametogenesis

BY1101 Introduction to Molecular and Cellular Biology

Stage 1: Gametogenesis

Stage 1:

Gametogenesis

Event

Production of gametes

Female (Ovum) Male (sperm)

Product

Haploid gametes

what are the major events in fertilisation

BY1101 Introduction to Molecular and Cellular Biology

What are the major events in fertilisation?

1. Contact

2. Acrosomal reaction

3. Interaction of gametes

4. Fusion of nuclei

what are the two defences to polyspermy

BY1101 Introduction to Molecular and Cellular Biology

What are the two defences to polyspermy?
  • Fast block against polyspermy
  • Acrosomal reaction -> Depolarisation
  • Slow block against polyspermy
  • Cortical reaction -> Fertilization envelope

Why is polyspermy a problem?

stage 2 fertilisation

BY1101 Introduction to Molecular and Cellular Biology

Stage 2: Fertilisation

Stage 2:

Fertilisation

Event

Fusion of haploid gametes (ovum + sperm) to produce a diploid zygote

Product

A diploid zygote

what are the major events in cleavage

BY1101 Introduction to Molecular and Cellular Biology

What are the major events in cleavage?
  • Rapid cell division of zygote into blastomeres
  • 5-7 divisions forms a ball of cells: Morula
  • Fluid filled cavity is the blastocoel
  • Surrounding hollow ball of cells are the blastula

Blastomeres

Morula

Blastula

Blastocoel

Fertilised zygote

Early

division

Early

cleavage

Late

cleavage

what is a major factor that influences cleavage

BY1101 Introduction to Molecular and Cellular Biology

What is a major factor that influences cleavage?
  • Yolk proteins – importance constituent of developing embryos
  • Proportion varies across species
  • Yolk affects cleavage
  • Greater aggregation at

vegetal pole

Animal pole

Vegetal pole

is cleavage different in the chick

BY1101 Introduction to Molecular and Cellular Biology

Is cleavage different in the chick?

All the cytoplasm of the cell is contained in a small disk

Cleavage planes cannot penetrate the yolk

Only cytoplasm at the animal pole is cleaved

Cleavage produces a small cap of cells – blastoderm

Blastoderm is the chick equivalent of blastula

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BY1101 Introduction to Molecular and Cellular Biology

Cleavage (Comparative)

Model organism

Sea urchin

Frog

Chick

Product of cleavage

Blastula

Blastula

Blastoderm

Type of cleavage

Holoblastic

Holoblastic

Meroblastic

stage 3 cleavage

BY1101 Introduction to Molecular and Cellular Biology

Stage 3: Cleavage

Stage 3:

Cleavage

Event

Rapid cell division without cell growth

Product

Blastula (Frog)/Blastoderm (Chick)

next step gastrulation

BY1101 Introduction to Molecular and Cellular Biology

Next step: Gastrulation

What is gastrulation?

  • A series of cell and tissue movements in which the blastula-stage embryo folds inward, producing a 3 layered embryo, the gastrula

Triploblastic – Three layers

Diploblastic – Two layers (Endo- and ectoderms only)

what differences occur in g astrulation of the frog

BY1101 Introduction to Molecular and Cellular Biology

What differences occur in gastrulation of the frog?

1. Cells begin to invaginate at the dorsal lip of the blastopore

2. Involution – Cells move over the dorsal lip and begin to move into the blastopore

3. Blastocoel collapses and is replaced by the archenteron

what differences occur in g astrulation of the chick

BY1101 Introduction to Molecular and Cellular Biology

What differences occur in gastrulation of the chick?

Two main cell types:

Epiblasts

All cells that will contribute to the formation of the embryo will originate as epiblasts

Hypoblasts

Functional in the normal formation of the primitive streak

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BY1101 Introduction to Molecular and Cellular Biology

Gastrulation (Comparative)

Model organism

Sea urchin

Frog

Chick

Site of involution during gastrulation

Blastopore

Blastopore

Primitive streak

stage 4 gastrulation

BY1101 Introduction to Molecular and Cellular Biology

Stage 4: Gastrulation

Stage 4:

Gastrulation

Event

Formation of the embryonic germ layers

Product

Gastrula (containing endoderm, mesoderm, ectoderm)

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BY1101 Introduction to Molecular and Cellular Biology

What is organogenesis?

  • The stage at which the embryonic germ layers localise into the basic structure of organs

How does it differ to gastrulation?

case study neurulation

BY1101 Introduction to Molecular and Cellular Biology

Case study: Neurulation

What are the steps involved in neurulation?

First steps in brain and spinal cord

Mesodermal cells form the notochord

Ectodermal cells above form the neural plate

Neural plate folds inwards to form the

neural tube

Neural tube will become the brain and spinal chord in the embryo

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BY1101 Introduction to Molecular and Cellular Biology

What are the two sets of specialised cells associated with neurulation?

Neural crest cells

Location: Borders from where the notochord pinches off from the ectoderm

Function: Formation of peripheral nerves, teeth and skull bones

Somites

Location: Groups of cells located in strips of mesoderm lateral to the notochord form blocks

Function:Segmentation of the body structure, vertebrae

slide29

BY1101 Introduction to Molecular and Cellular Biology

What are the four types of extra-embryonic membranes seen in the chick?

  • Allantois-
  • Waste disposal sac
  • Also gas exchange
  • Amnion-
  • Fluid filled sac
  • Bathes the embryo

Form during organogenesis

- Endoderm

- Mesoderm

- Ectoderm

  • Chorion-
  • Outer membrane
  • Gas exchange
  • Yolk sac-
  • Encloses the yolk
  • Blood vessels develop to bring nutrients
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BY1101 Introduction to Molecular and Cellular Biology

Stage 5: Organogenesis

Stage 5:

Organogenesis

Event

Formation of organs from the 3 germ layers formed during gastrulation

Product

Internal organs

exam questions

BY1101 Introduction to Molecular and Cellular Biology

Exam Questions

Notochord

Neural plate

Neural folds

Neural tube

Neural crest cells

exam questions1

BY1101 Introduction to Molecular and Cellular Biology

Exam Questions

Gametogenesis

Fertilisation

Cleavage

Gastrulation

Organogenesis

essay practice

BY1101 Introduction to Molecular and Cellular Biology

Essay practice

Q. 5 What is organogenesis? Describe the importance of neurulation in establishing the body plan of the embryo.

Write an introductory paragraph to the essay above.

- Introduction should address the question being asked

- Should be concise (max. 1 paragraph)

Using bullet points, outline the main concepts you would have in your main text body to support your answer

- Including labelled drawings to support your answer are recommended

Write a concluding paragraph

- Should readdress the question

- Summarise the main points from your essay

- Be concise (max. 1 paragraph)

- Should not include any new information

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BY1101 Introduction to Molecular and Cellular Biology

Next week:

Developmental genetics

Further reading:

Campbell Chapter 47

slide38

BY1101 Introduction to Molecular and Cellular Biology

Questions

Further reading:

Campbell Chapter 47

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