Developmental Concepts and Genetic Bases

Question 1

Determination

Answer 1

not visible, but irreversible commitment to differentiation

Question 2

Differentiation

Answer 2

expression of the developmental commitment; usually involves synthesis of cell-type specific proteins

Question 3

Morphogenesis

Answer 3

shaping of the multicellular body and its organs; pattern formation

Question 4

Muscle cell differentiation

Answer 4

1. Determination: signals from other cells lead to activation of myoD, committing the cell to becoming a skeletal muscle cell
2. Differentiation: synthesis of myoD protein further stimulates myoD and ultimately other muscle cell-specific genes such as myosin

Question 5

What other function does myoD do besides turning on genes for myosin and other muscle proteins?

Answer 5

Also turns on genes that block cell division (multinucleate muscle cells)

Question 6

Weismann’s Hypothesis (1892)

Answer 6

Determination is caused by segregation of developmental determinants by cell mitoses (at the cleavage stages)

Question 7

John Gurdon’s nuclear transplantation experiments in frogs (1968)

Answer 7

1. Frog egg cell + UV
2. Enucleated egg cell
3. Fully differentiated intestinal cell nucleus was transplanted into enucleated cell
4. Egg w/ donor nucleus began to develop
5. Tadpole

Question 8

What are the 2 conclusions from Gurdon’s experiment?

Answer 8

1. Somatic nuclei are totipotent; therefore, genes are not segregated to different cell types during development
2. Prolonged exposure to an egg environment is necessary to allow “de-differentiation” of a somatic nucleus to an egg-like status

Question 9

Development involves a reversible change in the genetic material: ____________________, not gene segregation

Answer 9

gene regulation

Question 10

Ian Wilmut and colleagues experiment (1997)

Answer 10

1. Starved somatic sheep cells (arrested them in G1 phase of cell cycle)
2. Diploid cells were fused w/ enucleated eggs from a different ewe and stimulated to enter S phase
3. Embryos were transplanted to the womb of a surrogate mother ewe
4. One lamb survived to birth and was genetically identical to Sheep 1 (somatic cells)

Question 11

What is the name of the famous sheep that was cloned?

Answer 11

Dolly

Question 12

Carrot root cells and totipotency

Answer 12

A carrot root cell can be induced to form a mass of cells called a callus. The callus can grow an entire new plant, meaning that each plant cell is “totipotent.” This makes transgenic plants easier to make.

Question 13

What is the “epigenetic landscape”?

Answer 13

the idea that developmental events channel determination to a final differentiated cell fate (totipotency decreases as developmental time goes on)

Question 14

What are stem cells?

Answer 14

Undifferentiated, dividing cells that are found in embryos and adults

Question 15

Where are the most adult stem cells found?

Answer 15

bone marrow, skin, and intestine (need frequent cell replacement)

Question 16

Are adult stem cells totipotent or pluripotent?

Answer 16

Pluripotent: limited ability to differentiate into a restricted number of different cell types

Question 17

Are embryo stem cells totipotent or pluripotent?

Answer 17

totipotent

Question 18

How are embryonic stem cells removed?

Answer 18

They are taken from the Inner Cell Mass (ICM) of a blastocyst

Question 19

Parkinson’s Disease

Answer 19

A common neurodegenerative disease
Cause: progressive degeneration of dopamine-containing neurons in a part of the brain called substantia nigra (SN)
Symptoms: tremor, muscle rigidity and weakness, speech difficulties, dementia, and a blank, mask-like facial expression

Question 20

How can embryonic stem cells possibly cure Parkinson’s?

Answer 20

Embryonic stem cells can be implanted into the SN region, where they’ll hopefully differentiate into dopamine-producing cells and relieve symptoms of the disease

Question 21

What is therapeutic cloning?

Answer 21

Process that involved fusing a cell nucleus from the affected person w/ an enucleated egg cell to make a blastocyst. The ICM from this blastocyst can differentiate into the desired tissue for transplantation w/o risk of immune system rejection (from using stem cells from another person)

Question 22

What are cytoplasmic determinants?

Answer 22

Possible proteins or mRNAs in the egg/zygote that are segregated to different cells in the embryo and that turn on differential gene expression and/or regulate spatial events of development

Question 23

What is induction?

Answer 23

Communication between different cell types that leads to increasingly specific developmental fates

Question 24

Induction process

Answer 24

1. the release of molecules from one cell that diffuse to adjacent cells and act on signal transduction pathways
2. direct cell-to-cell contact of surface molecules on the sending cell to receptor molecules on the receiving cell
   Ultimate outcome: turn on/turn off genes in the receiving cell

Question 25

Why is programmed cell death (apoptosis) a part of development?

Answer 25

Can lead to modeling of the morphology of organs and limbs
Ex: paw development in mouse embryo

Question 26

What is segmentation?

Answer 26

the formation of patterns during development

Question 27

Segmentation in Drosophila

Answer 27

-unequal distribution of mRNAs and/or proteins in the egg leads to gradients of morphogens in the zygote
-morphogens: bicoid (anterior larval development) and nanas (posterior larval development)

Question 28

Developmental steps in Drosophila

Answer 28

1. Egg cell w/ nurse cells
2. Early embryo that is multinucleate single cell
3. Segmented late embryo
4. Segmented larva
5. Pupariation (imaginal discs)
6. Adult w/ clear and complex segmentation pattern

Question 29

Bicoid and nanas are examples of ___________________________.

Answer 29

maternally determined morphogens

Question 30

What are the three types of segmentation genes that are induced by maternally determined morphogen gradients?

Answer 30

1. Gap genes
2. Pair Rule genes
3. Segment Polarity genes

Question 31

Gap genes

Answer 31

define broad areas that regulate pair rule genes

Question 32

Pair Rule genes

Answer 32

refine the segment locations and regulate segment polarity genes

Question 33

Segment Polarity genes

Answer 33

determine the final boundaries of each segment

Question 34

What are homeotic genes?

Answer 34

Genes that define the role of each segment once the locations of segments are established

Question 35

What happens if there’s mutations in homeotic genes?

Answer 35

The definitions of the role of each segment can be disrupted
Ex: bithorax on a fly (2 sets of abdomens > 2 sets of wings)

Question 36

Homeobox?

Answer 36

180-nucleotide sequence that encodes a 60-amino acid homeodomain in the protein = Hox genes

Question 37

What controls differentiation on the anterior-posterior axis of vertebrates and invertebrates?

Answer 37

Hox genes

Question 38

__________ and ___________ expression of Hox genes follows the same pattern as the linear order on chromosomes

Answer 38

Temporal, spatial

Question 39

Epigenetic Landscape and its channels

Answer 39

-Morphogens/gradients determine zones
-Regional developmental genes (gap, pair-rule, segment polarity) determine segments
-Hox genes determine identity
-Master developmental genes (myoD) determine subregion
-Specific functional genes (cell-type specific genes) determine function/physiology

Question 40

Connection of developmental channeling and evolution

Answer 40

homologous limbs, comparative embryology

Question 41

Neoteny

Answer 41

retention of juvenile characteristics in the adults of species (shrimps)