Development 2: What controls development?

Question 1

What are the 3 control factors in development?

Answer 1

Cytoplasm (epigenetic)
External environment (epigenetic)
Genes (genetic)

Question 2

During embryonic development, what normal DNA process is ‘turned off’?

Answer 2

Transcription

Question 3

What is the cytoplasm’s role in embryonic development?

Answer 3

Controls metabolic cycles and instructions for driving cell division

Question 4

Early development is controlled by which parent?

Answer 4

Maternally controlled, cytoplasm comes from mother

Question 5

What is genomic activation?

Answer 5

change from maternal control to embryo control

Question 6

Describe what happens once genomic activation has occurred.

Answer 6

• Embryonic DNA starts transcription = cell division
• Cell division slows down (because transcription & translation take time) = how this stage is identified

Question 7

What does cell differentiation result from?

Answer 7

differential gene expression (certain genes are switched off = cell function)

Question 8

What is differential gene expression influenced by?

Answer 8

the cytoplasm and the extracellular environment

Question 9

Describe the results of the Experiment on frogs to test the role of cytoplasm on differentiation

Answer 9

Genomic equivalence = No info is lost in the early stages of development (every nucleus in every somatic cell contains all the genes for creating a whole new individual)

= Shows the cytoplasm controls the fate of a nucleus

Question 10

Describe cytoplasmic segregation in development

Answer 10

when a factor is unequally distributed in the cytoplasm and ends up in some daughter cells but not in others, or in greater conc.s than in others
= cause differentiation of cells due to animal and vegetal poles differing in their developmental potential

Question 11

Define induction in development

Answer 11

When a factor is secreted by some cells to induce others to differentiate

Question 12

Describe primary induction in birds and amphibians

Answer 12

• In amphibians, cells moving over the dorsal lip of the blastopore (Spemann organiser) induce overlying ectoderm to form neural tissue
• In birds, cells moving over Hensen’s node are induced to form the CNS

Question 13

The development of which sensory organ is an example of secondary induction?

Answer 13

the vertebrate eye

Question 14

How do cells ‘know’ where they are in an animal?

Answer 14

By interpretating positional info = conc. gradient of a morphogen

Question 15

A signal is a morphogen if …

Answer 15

• It directly affects target cells (does not work through an intermediary)
• Diff conc.s cause different effects

Question 16

What is genomic imprinting?

Answer 16

in mammals some development genes are active only if they come from a sperm OR egg

Question 17

What are segmentation genes?

Answer 17

they influence the number, boundaries, and polarity of the body segments

Question 18

What do gap genes do in body segmentation?

Answer 18

organise large areas along the anterior large areas along the anterior-posterior

Question 19

What do pair rule genes do in body segmentation?

Answer 19

divide the embryo into units of 2 segments each

Question 20

What do segment polarity genes do in body segmentation?

Answer 20

determine segment boundaries

Question 21

What do homeotic (hox) genes do in body segmentation?

Answer 21

are expressed along the length of the body and determine what the segments will become

Question 22

Describe how body segmentation is controlled in mice

Answer 22

• 4 families of homeotic genes (hox genes) control differentiation along the axis
• Temporal and spatial pattern of expression of hox genes is tied together → also follows the linear order on the chromosome

Question 23

How do hox genes control segmentation? What do mutations result in?

Answer 23

they specify the properties of each segment, mutations in these can change a segments identity

Question 24

What is apoptosis?

Answer 24

programmed cell death, caused by the activation of ‘death’ genes

Question 25

Give an example of apoptosis in human development

Answer 25

In development, we have webbed hands and feet - the enzyme caspase stimulates apoptosis of this extra skin

Question 26

Give en example showing why environmental factors can be necessary for successful development

Answer 26

House mice raised in microbe-free environments lack gut bacteria - Gut bacteria induce gene expression in the intestine which is essential for normal capillary development

Question 27

Give an example of environmental factors disrupting development

Answer 27

Cyclopamine inhibits the action of the Sonic Hedgehog protein, which is involved in the formation of the neural system

Question 28

Give an example of a developmental stage that is under both genetic and environmental control

Answer 28

Neurulation: primarily under genetic control, but environ derived material e.g vitamins and minerals are also needed = neural tube defects can be reduced if the pregnant person receives enough folic acid