Regulation of Gene Expression

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13

Fig. 18-19b

Fertilization,

translation

of bicoid

mRNA

Bicoid protein in early

embryo

Anterior end

Bicoid mRNA in mature

unfertilized egg

100 µm

RESULTS

Slide 92

Fig. 18-19c

bicoid mRNA

Nurse cells

Egg

Developing egg

Bicoid mRNA in mature

unfertilized egg

Bicoid protein

in early embryo

CONCLUSION

Slide 93

This phenotype suggests that the product of the mother’s bicoid gene is concentrated at the future anterior end

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

Slide 94

The bicoid research is important for three reasons:

– It identified a specific protein required for some early steps in pattern formation

– It increased understanding of the mother’s role in embryo development

– It demonstrated a key developmental principle that a gradient of molecules can determine polarity and position in the embryo

Slide 95

Concept 18.5: Cancer results from genetic changes that affect cell cycle control

The gene regulation systems that go wrong during cancer are the very same systems involved in embryonic development

Slide 96

Types of Genes Associated with Cancer

Cancer can be caused by mutations to genes that regulate cell growth and division

Tumor viruses can cause cancer in animals including humans

Slide 97

Oncogenes and Proto-Oncogenes

Oncogenes are cancer-causing genes

Proto-oncogenes are the corresponding normal cellular genes that are responsible for normal cell growth and division

Conversion of a proto-oncogene to an oncogene can lead to abnormal stimulation of the cell cycle

Slide 98

Fig. 18-20

Normal growth-

stimulating

protein in excess

New

promoter

DNA

Proto-oncogene

Gene amplification:

Translocation or

transposition:

Normal growth-stimulating

protein in excess

Normal growth-

stimulating

protein in excess

Hyperactive or

degradation-

resistant protein

Point mutation:

Oncogene

Oncogene

within a control element

within the gene

Slide 99

Proto-oncogenes can be converted to oncogenes by