Regulation of Gene Expression

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siRNAs and miRNAs are similar but form from different RNA precursors

Slide 59

Chromatin Remodeling and Silencing of Transcription by Small RNAs

siRNAs play a role in heterochromatin formation and can block large regions of the chromosome

Small RNAs may also block transcription of specific genes

Slide 60

Concept 18.4: A program of differential gene expression leads to the different cell types in a multicellular organism

During embryonic development, 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

Slide 61

A Genetic Program for Embryonic Development

The transformation from zygote to adult results from cell division, cell differentiation, and morphogenesis

Slide 62

Fig. 18-14

(a) Fertilized eggs of a frog

(b) Newly hatched tadpole

Slide 63

Fig. 18-14a

(a) Fertilized eggs of a frog

Slide 64

Fig. 18-14b

(b) Newly hatched tadpole

Slide 65

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

Slide 66

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, cells contain different cytoplasmic determinants, which lead to different gene expression

Slide 67

Fig. 18-15

(b) Induction by nearby cells

(a) Cytoplasmic determinants in the egg

Two different

cytoplasmic

determinants

Unfertilized egg cell

Sperm

Fertilization

Zygote

Mitotic

cell division

Two-celled

embryo

Signal