Unit 13- Development and its Genetic Control

The development of a complex adult organism from a single cell is the result of a number of complex processes we summarize as “embryology”. In this chapter we will explore that development

General pattern of Development

Early Ideas About Development

1600’s- Preformation Theory-

1.  ovists-

2.  spermists-

late 1600’s- Theory of Epigenesis-

modern belief- morphogenesis-

Events in a Life

1. Fertilization- a sperm n joins with an ovum n to make a zygote 2n

3 functions of fertilization

1.

2.

3.

Four Steps of Fertilization

1.  Sperm Contacts Egg and Recognizes its Surface

2.  Sperm Enters the Egg

3.  Fusion of the Pronuclei

4.  Activation of the Egg

Types of Egg Arrangement

1.  telolecithal-

2.  hololecithal-

Embryonic Development

Suppie sites- http://courses.biology.utah.edu/bastiani/3230/DB%20Lecture/Lectures/Lec6Gast.html

Or

http://www.brynmawr.edu/biology/271/LecSlides/Lec19.pdf

cleavage- defn-

Steps of Cleavage

Fates of the 3 Germ Layers

1.  endoderm-

2.  mesoderm-

3.  ectoderm-

coelom-defn:-

Patterns of Cleavage

1.  radial cleavage-

2.  spiral cleavage-

What are Protostomes and Deuterostomes?

1.  Protostomes-

Ex:

2.  Deuterostomes-

ex:

Patterns of Cleavage 2-

1.  holoblastic-

2.  meroblastic-

blastodisc-

Pattern for the Chick

The chick blastodisc has been much studied and is fairly well understood

Cephalization diagram

Extraembryonic Membranes

Cleidoic egg-

In vertebrates the developing embryo is aided by 4 special membranes that have their own life support functions

Placental Mammals- diagram

Note*

So what does all this have to do with genetic controls on development?

Recall: development consists of differentiation and determination

In early embryos cells are ______- position, time and genetics determines their fate

Examples of Totipotency

1.  plant tissue culture- a procedure widely used in agriculture to clone pure strains- mericloning

1958- F. C Steward- carrot callous experiments

2.  Nuclear Transplantation Experiments

Briggs, King and Gurdon-

A series of experiments working with frog eggs

Experiments-

3. Drosophila studies in differential gene activity

Differential activity-

These studies analyzed the many mutations fruit flies develop

Genes Known in Drosophila

1.  Maternal Effect Genes-

2.  Segmentation genes-

A.  gap genes-

B.  pair rule genes-

C.  segment polarity genes-

3.  Homeotic Genes (Hox genes)-

4.  Mapping of Cell Fates in Caenorhabditis

C. elegans is an easily cultured nematode with about 1000 cells

A fate map of all the cells lives has been formed and is found to have three main paths

5. Mouse Genetics- making Chimaeras

Chimaera-

1