Ch 20 Developmental genetics

Question 1

Multicellular organisms

Answer 1

Share many genes, genetic pathways, and molecular signaling mechanisms that control developmental events from zygote to adult.

Question 2

Development at cellular level marked by three important events

Answer 2

1. Specification: First cues confer spatially distinct identity.
2. Determination: Specific developmental fate for cell becomes fixed.
3. Differentiation: Cell achieves final adult form and function

Question 3

Development and what developmental geneticists study

Answer 3

Development: attainment of differentiated state by all cells in an organism
Developmental geneticists study
– What genes are expressed and when
–In what part of developing embryo genes are expressed
–How expression of genes is regulated
–Result of defective genes

Question 4

Variable gene activity

Answer 4

Variable gene activity hypothesis
–Differentiation accomplished by activating and inactivating genes at different times in different cell types
–Assumes
1. Cell contains entire genome
2. Different transcription of selected genes controls development and differentiation of each cell

Question 5

Homeotic genes (Hox genes)

Answer 5

genetic analysis shows:
- size and shape of all animal bodies controlled by a common set of genes and developmental mechanisms
homeotic genes
Homeotic genes (Hox genes)
- Single set of genes with different patterns of expression
- Homeotic genes from wide range of organisms have a common ancestry.

Question 6

Analysis of Developmental Mechanism

Answer 6

General processes in development
– How adult body plan is laid down in embryo
–Program of gene expression turns undifferentiated cells into differentiated cells.
–Role of cell–cell communication in development

Question 7

Overview of Drosophila Development

Answer 7

Drosophila development
–Ten-day cycle
–Five distinct phases before adult stage
1. Embryo
2-4. Three larval stages
5. Pupal stage
    Adult stage

Question 8

Early stages of development in Drosophila

Answer 8

–Egg is fertilized
–Nucleus begins multiple rounds of division
–After tenth division, nuclei migrate to periphery of egg.
–Germ cells form.
–Nuclei are enclosed in membrane (blastoderm).
–Segmentation pattern is established.

Question 9

Genetic Analysis of Embryogenesis

Answer 9

Two different gene sets control embryonic development in Drosophila.
–Maternal-effect genes
–Zygotic genes

Question 10

Maternal-effect genes

Answer 10

• mRNA and proteins are deposited in egg cytoplasm.
• Products are distributed in gradient or concentrated in specific regions of cell.
• Encode transcription factors and proteins
  1. Regulate gene expression
  2. Products activate or repress expression of zygotic genome.

Question 11

Maternal-effect gene products

Answer 11

anterior, posterior gradient formed by maternal genes
– Placed in egg during oogenesis
– Activated immediately after fertilization
–Establish anterior-posterior axis of embryo
– Encode transcription factors
1. Activate transcription of zygotic genes which divide embryo into head, thorax, and abdominal regions of adult

Question 12

Zygotic genes

Answer 12

Divide embryo into broad regions
–Transcribed in nuclei of developing embryo
–Transcribed in specific regions in response to distribution of maternal-effect proteins

Question 13

Gap genes

Answer 13

–Transcription of gap genes divides embryo into head, thorax, and abdomen
–Gap genes encode transcription factors that bind to enhancer regions controlling expression of pair-rule genes.

Question 14

Pair-rule genes

Answer 14

Expression of pair-rule genes

• Establishes boundaries of segments
• Establishes developmental fate of cells within each segment by controlling expression of segment polarity genes

Question 15

Segment polarity genes

Answer 15

Expression of segment polarity genes
–Controlled by transcription factors encoded by pair-rule genes
–Regulate the spacial pattern of differentiation within each segment of the developing embryo and identify the anterior-posterior axes

Question 16

Homeotic Selector Genes Specify Parts of the Adult Body

Answer 16

Homeotic genes (selector genes)
–Activated as targets of zygotic genes
–Selector genes: determine which adult structures will be formed by each body segment (antennae, mouth parts, legs, wings, thorax, and abdomen)

Question 17

Summary

Answer 17

1. Gap genes are activated to subdivide embryo into broad bands.
2. Gap genes activate pair-rule genes, which divide embryo into segments.
3. Segment polarity genes divide each segment into anterior-posterior axes, which are then given identity by Hox genes.