Lecture 11&12- Animal Development & Ageing

Question 1

What is the fertilized egg called?

Answer 1

Zygote, one celled, formed right after fertilization?

Question 2

What initially happens after fertilization? *photo

Answer 2

Zygote divides uniformly (2,4,8,16…), where it then forms a Morula (solid ball of cells)

Question 3

What is a blastula?

Answer 3

It is a stage in cellular development where a blastocoel (fluid filled cavity) is present, as a result of cells growing away from a center (still no differentiated cells)

Question 4

What happens during early gastrula?

Answer 4

• Blastula starts differentiating into ectodermal tissues and endodermal tissue
• archenteron forms as a result of the endoderm evaginating the blastocoel, forming a small cavity on the outside called a blastopore
• Organism is now 2 layered

Question 5

What characterizes the late gastrula stage?

Answer 5

• Formation of the mesoderm via help from the endoderm and ectoderm
• closing off the blastopore

Question 6

What are the endoderm, mesoderm and ectoderm referred to as?

Answer 6

Embryonic germ layers

Question 7

What is another name for archentron?

Answer 7

Primitive gut- it is the endoderm

Question 8

What does the Ectoderm form?

Answer 8

• Nervous system
• skin epidermis, and derivatives of them (hair,nails,glands)
• tooth enamel, dentin, and pulp
• epithelial lining of the oral cavity and rectum

Question 9

What does the Mesoderm form?

Answer 9

• Musculoskeletal system
• skin dermis
• cardiovascular system
• urinary system
• lymphatic system
• reproductuve system
• most epithelial linings
• outer layers of respiratory and digestive systems

Question 10

What does the endoderm form?

Answer 10

• epithelial lining of the digestive tract and respiratory tract (and their glands)
• epithelial lining of urinary bladder, thyroid and parathyroid glands

Question 11

What is the Morula?

Answer 11

Stage in cell development where the organism is a solid mass of cells, after zygote

Question 12

Describe the process of development of the nervous system in chordates

Answer 12

• Nervous system develops from the midline ectoderm by thickening of cells to form the neural plate
• two neural ends fold on either side of the neural plate to create a neural groove that eventually fuses into the neural tube
• Anterior (nearer to front ) end of the neural tube develops into the brain, rest is the spinal cord

Question 13

What are the three interconnected developmental processes?

Answer 13

• Growth- through Mitosis
• Differentiation- in structure and function
• Morphogenesis- cell movement and pattern formation ​to -produce shape of organism’s body

Question 14

Give 2 examples of model organisms used to research developmental genetics?

Answer 14

roundworm- C, elegans

Fruitfly- Drosphilia melanogaster

Question 15

What are Maternal Determinants?

Answer 15

• They are mRNA or protein molecules initially present in the egg cytoplasm, stimulate early processes of development
• Segregation of MDs determine the types of cells and organs developing from the three germ layers; also help form the body axis
• Are unequally distributed during mitosis
• eventually run out

Question 16

How do cells differentiate after MD’s are used up?

Answer 16

• Inducing development by signals called inducers(proteins), that are released by neighboring cells (eg Differenciated cell sends signal to undifferentiated cell to differentiate)
• inducers activate expression of particular genes
• ∴ induction requires transcriptional regulation of genes in a precise sequence

Question 17

How is induction brought about in C. elegans for vulva formation?

Answer 17

• ​anchor cell induces vulva formstion
• cells closest to anchor cell receive the most inducers and develop into inner vulva
• inner vulva cells produce other inducers, neighboring cells differentiate to outer vulva

Question 18

What is pattern formation?

Answer 18

The process that enables mrophogenesis

ensures proper strategic cell movement and organization so morphogenesis takes place

Question 19

How is pattern formation regulated?

Answer 19

by the transcription of various gene sets

Question 20

Give an example as to why apoptosis is important?

Answer 20

the formation of webbed hands/feet

Question 21

What are egg polarity genes?

Answer 21

• they are genes that establish antereoposterior polarity (head/back side)
• they are present before egg fertilization
• they express MD’s in the form of mRNA that will be translated into proteins upon fertilization and will form gradients (morphogenes

Question 22

What is the function of morphogenes?

Answer 22

Activate the expression of segmentation genes

Question 23

What are zap genes?

Answer 23

• they are zygotes genes that are activated by the anterioposterior morphogene gradients
• divide the anterioprosterior axis into broad regions
• activate pair-rule genes

Question 24

What are pair-rule genes?

Answer 24

• Genes that are expressed in alternating stripes
• body segments are formed along the antereoposterior axis
• Their protein products activate or suppress the expression of segment-polarity genes

Question 25

What are segment polarity genes?

Answer 25

• genes that ensure that each segment has boundaries
• expressed in striped fashion
• twice as many stripes as pair-rule genes

Question 26

What are homeotic genes?

Answer 26

• highly conserved genes (selector genes)
• found in many genomes including mice and humans
• code for Transcriptor factors (tf’s) that regulate which genes should be switched on/off
• homeotic tf’s dictate which body parts arise from which body segment
• mutations result in development of body parts in inappropriate areas