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Midterm exam: A more detailed look… 45 multiple-choice questions (1 point each = 45 points) 5 math questions w/ calculator (1 point each = 5 points) 1 “long” (3-part) FRQ (30 points = 30 points) 3 “short answer” FRQ parts (20 pts = 20 points) TOTAL = 100 points.

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slide1

Midterm exam: A more detailed look…

  • 45 multiple-choice questions (1 point each = 45 points)
  • 5 math questions w/ calculator (1 point each = 5 points)
  • 1 “long” (3-part) FRQ (30 points = 30 points)
  • 3 “short answer” FRQ parts (20 pts = 20 points)
            • TOTAL = 100 points

We’ll be doing an in-class review session on Friday and additional review

during the scheduled afternoon sessions next week.

ch 21 the genetic basis of development

Ch. 21: The Genetic Basis of Development

The development of an organism from a zygote to an embryo to an adult is a delicate process that involves much genetic control!

slide3

Chapter 21: The Genetic Basis of Development

  • How do we study development in the genetics-based lab?

-Model organisms

-fruit fly, nematode worm, mouse, etc.

figure 21 2 model organisms for genetic studies of development

DROSOPHILA MELANOGASTER

(FRUIT FLY)

CAENORHABDITIS ELEGANS

(NEMATODE)

Figure 21.2 Model Organisms for Genetic Studies of Development

Drosophila

- small, easy & cheap to culture

- 2 week generation time

- 4 chromosomes

- LARGE literature of info

C elegans

- easy to culture

- transparent body with few cell types

- zygote to mature adult in 3 days

0.25 mm

slide5

Chapter 21: The Genetic Basis of Development

Zygote

0

First cell division

Germ line

(future

gametes)

Outer skin,

nervous system

Nervous

system,

outer

skin, mus-

culature

Musculature,

gonads

Time after fertilization (hours)

Musculature

10

Hatching

Intestine

Intestine

Eggs

Vulva

ANTERIOR

POSTERIOR

1.2 mm

-The complete cell lineage of the C. elegans nematode is known…

slide6

ARABIDOPSIS THAMANA

(COMMON WALL CRESS)

MUS MUSCULUS

(MOUSE)

DANIO RERIO

(ZEBRAFISH)

Mouse

- vertebrate

- LARGE literature

- transgenics & knock-outs

slide7

Chapter 21: The Genetic Basis of Development

(b) Tadpole hatching

from egg

(a) Fertilized eggs

of a frog

Figure 21.3a, b

  • How does a zygote transform into an organism?
  • Cell division

2) Cell differentiation

3) Morphogenesis—”creation of form/shape”

slide8

(a)

Animal development. Most

animals go through some

variation of the blastula and

gastrula stages. The blastula is

a sphere of cells surrounding a

fluid-filled cavity. The gastrula

forms when a region of the blastula

folds inward, creating a

tube—a rudimentary gut. Once

the animal is mature,

differentiation occurs in only a

limited way—for the replacement

of damaged or lost cells.

Gut

Cell

movement

Zygote

(fertilized egg)

Eight cells

Blastula

(cross section)

Gastrula

(cross section)

Adult animal

(sea star)

Cell division

Morphogenesis

Observable cell differentiation

(b)

Plant development. In plants

with seeds, a complete embryo

develops within the seed.

Morphogenesis, which involves

cell division and cell wall

expansion rather than cell or

tissue movement, occurs

throughout the plant’s lifetime.

Apical meristems (purple)

continuously arise and develop

into the various plant organs as

the plant grows to an

indeterminate size.

Seed

leaves

Shoot

apical

meristem

Root

apical

meristem

Zygote

(fertilized egg)

Two cells

Embryo

inside seed

Plant

Figure 21.4a, b

slide9

Chapter 21: The Genetic Basis of Development

  • How do we study development in the genetics-based lab?
  • How does a zygote transform into an organism?
  • How do cells become differentiated?

-All cells have the same DNA, so differential gene expression must be the explanation!

slide10

Researchers enucleated frog egg cells by exposing them to ultraviolet light, which

destroyed the nucleus. Nuclei from cells of embryos up to the tadpole stage were transplanted into the

enucleated egg cells.

EXPERIMENT

Frog tadpole

Frog egg cell

Frog embryo

Fully differ-

entiated

(intestinal) cell

Less differ-

entiated cell

Donor

nucleus

trans-

planted

Enucleated

egg cell

Donor

nucleus

trans-

planted

<2% develop

into tadpoles

Most develop

into tadpoles

Figure 21.6

  • -Once a cell is differentiated, it’s difficult to “de-differentiate.”
however plants behave differently

Transverse

section of

carrot root

CONCLUSION

EXPERIMENT

2-mg

fragments

Fragments cul-

tured in nutrient

medium; stir-

ring causes

single cells to

shear off into

liquid.

Single cells

free in

suspension

begin to

divide.

Embryonic

plant develops

from a cultured

single cell.

Plantlet is cul-

tured on agar

medium. Later

it is planted

in soil.

A single

Somatic (nonreproductive) carrot

cell developed into a mature carrot

plant. The new plant was a genetic

duplicate(clone) of the parent plant.

RESULTS

Adult plant

At least some differentiated (somatic) cells in plants are totipotent, able

to reverse their differentiation and then give rise to all the cell types in a mature plant.

Figure 21.5

However, plants behave differently…
slide12

Egg cell

donor

Mammary

cell donor

APPLICATION

This method is used to produce cloned

animals whose nuclear genes are identical to the donor

animal supplying the nucleus.

1

2

Egg cell

from ovary

Nucleus

removed

Nucleus

removed

Cells fused

Cultured

mammary cells

are semistarved,

arresting the cell

cycle and causing

dedifferentiation

3

TECHNIQUE

Shown here is the procedure used to produce

Dolly, the first reported case of a mammal cloned using the nucleus

of a differentiated cell.

Nucleus from

mammary cell

Grown in culture

4

RESULTS

The cloned animal is identical in appearance

and genetic makeup to the donor animal supplying the nucleus,

but differs from the egg cell donor and surrogate mother.

Early embryo

Implanted in uterus

of a third sheep

5

Surrogate

mother

Embryonic

development

6

Lamb (“Dolly”)

genetically identical to

mammary cell donor

Figure 21.7

slide13

Chapter 21: The Genetic Basis of Development

Embryonic stem cells

Adult stem cells

Early human embryo

at blastocyst stage

(mammalian equiva-

lent of blastula)

From bone marrow

in this example

Totipotent

cells

Pluripotent

cells

Cultured

stem cells

Different

culture

conditions

Liver cells

Blood cells

Nerve cells

Different

types of

differentiated

cells

Figure 21.9

4. What is a stem cell?

-a relatively unspecialized cell

-can differentiate into cells of different types under specific conditions

-Embryonic = totipotent

-Adult = pluripotent (can produce some, but not all, cell types)

slide14

Chapter 21: The Genetic Basis of Development

2

1

Nucleus

Master control gene myoD

Other muscle-specific genes

DNA

OFF

OFF

Embryonicprecursor cell

Determination. Signals from othercells lead to activation of a masterregulatory gene called myoD, andthe cell makes MyoD protein, atranscription factor. The cell, nowcalled a myoblast, is irreversiblycommitted to becoming a skeletalmuscle cell.

OFF

mRNA

MyoD protein(transcriptionfactor)

Myoblast (determined)

Differentiation. MyoD protein stimulatesthe myoD gene further, and activatesgenes encoding other muscle-specifictranscription factors, which in turn activate genes for muscle proteins. MyoD also turns on genes that block the cell cycle, thus stopping cell division. The nondividing myoblasts fuse to become mature multinucleate muscle cells, alsocalled muscle fibers.

mRNA

mRNA

mRNA

mRNA

Myosin, othermuscle proteins,and cell-cycleblocking proteins

MyoD

Anothertranscriptionfactor

Muscle cell(fully differentiated)

5. What type of genetic signal leads to cell differentiation?

-Step 1: Cell receives signals from other cells

-Step 2: A regulatory gene is turned “on”, and a protein is made that

activates other genes. (“point of no return”)

-Step 3: Activated genes make proteins that determine cell type/

structure/behavior.

slide15

Chapter 21: The Genetic Basis of Development

2

Posterior

1

Anterior

Signal

protein

4

3

Receptor

EMBRYO

3

4

Signal

Anterior

daughter

cell of 3

Posterior

daughter

cell of 3

Will go on to

form muscle

and gonads

Will go on to

form adult

intestine

(b)

Induction by nearby cells. The cells at the bottom of the early embryo depicted here are releasing

chemicals that signal nearby cells to change their gene expression.

(a)

Induction of the intestinal precursor cell at the four-cell stage.

6. What is induction?

-signal molecules (proteins or hormones) from embryonic cells cause

trancriptional changes in nearby target cells.

slide16

Epidermis

Signal

protein

Gonad

Anchor cell

Vulval precursor cells

Outer vulva

ADULT

Inner vulva

Epidermis

Figure 21.16b

(b)

Induction of vulval cell types during larval

development.

slide17

EXPERIMENT

RESULTS

CONCLUSION

Spemann and Mangold transplanted a piece of the dorsal lip of a pigmented newt gastrula to the

ventral side of the early gastrula of a nonpigmented newt.

Pigmented gastrula

(donor embryo)

Dorsal lip of

blastopore

Nonpigmented gastrula

(recipient embryo)

During subsequent development, the recipient embryo formed a second notochord and neural tube in

the region of the transplant, and eventually most of a second embryo. Examination of the interior of the double embryo

revealed that the secondary structures were formed in part from host tissue.

Primary embryo

Primary

structures:

Secondary (induced) embryo

Secondary

structures:

Neural tube

Notochord

Notochord (pigmented cells)

Neural tube (mostly nonpigmented cells)

The transplanted dorsal lip was able to induce cells in a different region of the recipient to form

structures different from their normal fate. In effect, the dorsal lip “organized” the later development of an entire embryo.

Figure 47.25

slide18

Chapter 21: The Genetic Basis of Development

Unfertilized egg cell

Molecules of a

a cytoplasmic

determinant

Fertilization

Nucleus

Zygote

(fertilized egg)

Mitotic cell division

Two-celled

embryo

(a)

Cytoplasmic determinants in the egg. The unfertilized egg cell has molecules in its cytoplasm,

encoded by the mother’s genes, that influence development. Many of these cytoplasmic

determinants, like the two shown here, are unevenly distributed in the egg. After fertilization

and mitotic division, the cell nuclei of the embryo are exposed to different sets of cytoplasmic

determinants and, as a result, express different genes.

Figure 21.11a

-cytoplasmic determinants in the unfertilized egg regulate gene

expression in the zygote that affects differentiation/development

slide19

Chapter 21: The Genetic Basis of Development

Tail

Head

T1

A8

T2

A7

T3

A6

A1

A5

A2

A4

A3

Wild-type larva

Tail

Tail

A8

A8

A7

A6

A7

Mutant larva (bicoid)

(a)

Drosophila larvae with wild-type and bicoid mutant phenotypes. A mutation

in the mother’s bicoid gene leads to tail structures at both ends (bottom larva).

The numbers refer to the thoracic and abdominal segments that are present.

Figure 21.14a

-Cytoplasmic determinants from mother’s egg initially establish the axes of

the body of Drosophila.

-bicoid gene

slide20

Egg cell

Nurse cells

Developing

egg cell

1

bicoid mRNA

Bicoid mRNA

in mature

unfertilized egg

2

Fertilization

100 µm

Translation of bicoid mRNA

Bicoid protein in

early embryo

3

Anterior end

(b) Gradients of bicoid mRNA and Bicoid protein in normal egg and early embryo.

Figure 21.14b

slide21

Chapter 21: The Genetic Basis of Development

Hierarchy of Gene Activity in Early Drosophila Development

Maternal effect genes (egg-polarity genes)

Gap genes

Segmentation genes

of the embryo

Pair-rule genes

Segment polarity genes

Homeotic genes of the embryo

Other genes of the embryo

-7. How does morphogenesis (pattern formation) occur in animals?

After the body’s axes are determined (by cytoplasmic determinants)…

-Segmentation genes produce proteins that direct formation of

body segments.

-Then, the development of specific features of the body segments is directed

by HOMEOTIC GENES (Hox genes.)

slide22

Chapter 21: The Genetic Basis of Development

Adult

fruit fly

Fruit fly embryo

(10 hours)

Fly

chromosome

Mouse

chromosomes

Mouse embryo

(12 days)

Adult mouse

Figure 21.23

8. What is the relationship among the genetic basis of development

across organisms?

-Molecular analysis of the homeotic genes in Drosophila has shown that they

all include a sequence called a homeobox

-An identical (or very similar) DNA sequence has been discovered in the

homeotic genes of vertebrates and invertebrates

slide23

Chapter 21: The Genetic Basis of Development

Ced-9

protein (active)

inhibits Ced-4

activity

Mitochondrion

Ced-4

Ced-3

Death

signal

receptor

Inactive proteins

Cell

forms

blebs

(a) No death signal

Ced-9

(inactive)

Death

signal

Active

Ced-3

Active

Ced-4

Other

proteases

Nucleases

Activation

cascade

(b) Death signal

9. What is apoptosis?

-programmed cell death (cell suicide)

Figure 21.18 Molecular basis of apoptosis in C. elegans

slide24

Chapter 21: The Genetic Basis of Development

Interdigital tissue

1 mm

Figure 21.19

8. What is apoptosis?

-programmed cell death (cell suicide)

-necessary for development of hands/feet in vertebrates

unit 6 test 2012 13
Unit 6 Test (2012-13)

Please take your test folder and learning log from the

table by the door!

  • Average: 19 / 30
  • Range: 8 – 28
  • Learning Logs: 8/10 needed for test corrections
    • 5 points for completion
    • 5 points for accuracy
  • Test Corrections: Due Wednesday, January 22nd
  • FOCUS ON MIDTERM PREP!!!
slide26

Welcome!

  • Before you begin…
  • 1) Please turn in food under computer tables and sign the log sheet. Thank you!
  • 2) Leave your test folder on top of your desk. I’ll collect them during the testing period and record your 10 point “learning log” bonus.
  • 3) Sign the honor code sheet on the front of your test packet. You may NOT write in the multiple-choice test booklet. (You may write on the math sheet and on the FRQ sheet.)
  • 4) Use the green side of your scantron, and make sure that you mark your KEY ID as either B or C.
  • 5) Make sure that your name is on your scantron, math sheet, and FRQ answer sheet before you turn them in.
  • 6) Good luck! I’m proud of your hard work this semester and look forward to finishing out the year!
    • *I have your Unit 6 Test FRQs graded if you’re interested in seeing them at the end of the period.
    • *MIDTERM test grades will be available on Tuesday, Jan. 22nd…we need to calculate the test average for ALL students before assigning a curve!