Review for Exam #3, Developmental biology.
Plant and flower development:
1. Identify the main differences between animal and plant development.
2. A fate map of the plant embryo can first be clearly drawn at which stage?
(a) egg
(b) two-cell
(c) octant
(d) heart
(e) the extremely regulative pattern of plant development prevents the construction of a
fate map at any stage
3. What is the evidence that differentiated plant cells are totipotent?
(a) both cells at the embryonic two-cell stage can give rise to an entire plant if separated
(b) cells from roots, stems, and leaves can be cultured in the presence of hormones and
will develop into seedlings
(c) differentiated plant cell nuclei are fused with enucleated egg cells and normal
development ensues
(d) isolated blastomeres will reinitiate development to form an embryo
(e) comparison of the genome in differentiated cells and gametes reveals that
differentiated cells retain all the genes in
the genome
4. The adult structures of a plant, such as leaves and flowers, arise from
(a) primordia established in the embryo
(b) imaginal cells set aside during embryogenesis
(c) a stem cell population in the meristems which continually produce differentiating cells
(d) outgrowths which occur periodically along the stem after the stem has elongated
(e) cotyledons
6. What is the origin of the floral meristem?
(a) special cells are set aside in the embryo which will later become floral meristem
(b) three meristems are established in the embryo: root, shoot, and floral
(c) axial buds are floral meristems
(d) shoot meristem becomes floral meristem under the influence of genes such as LEAFY
(e) cells from the root meristem will change their fate and become floral meristem
7. The central-most whorl of a floral meristem will become
(a) leaf
(b) sepal
(c) petal
(d) stamen
(e) carpel
8. The "ABC" model for floral identity predicts that the loss of a class C gene, which is
expressed in whorls 3 and 4, will
lead to a flower composed of
(a) sepal, petal, stamen, carpel, from outside to inside
(b) carpel, stamen, stamen, carpel, from outside to inside
(c) sepal, sepal, sepal, sepal, from outside to inside
(d) sepal, petal, petal, sepal, from outside to inside
(e) sepal, sepal, carpel, carpel, from outside to inside
Concept questions:
1. Contrast the plant meristem with embryonic cells in the animal blastula. In what ways
are they similar, and in what ways do they differ?
2. An adult differentiated plant cell can give rise to a whole new plant under appropriate
circumstances. Discuss the implication of this fact for the importance of maternal factors
packaged into the oocyte of plants.
9. How does clonal analysis allow the number of cells in the meristem that will give rise
to a particular leaf or other organ to be estimated?
12. The experiment shown in Figure 7.18 provides evidence for lateral inhibition in the
spacing of leaf primordia. Predict
the position of primordium number 4 if both primordium 1 and primordium 3 were
excised. Where might primordium 4
have formed if only primordium 2 had been excised?
13. What is the phenotype of a homeotic mutation in flowers? In what way are these
analogous to homeotic mutations in Drosophila?
14. Contrast the combinatorial code which directs petal formation with that which directs
stamen formation. What gene is expressed in petals which is not expressed in stamens?
What gene is in stamens but not petals? What gene is common to both?
15. Predict the phenotype of a flower which is mutant for both pistillata and agamous.
What is the genetic interaction
that occurs between the three classes of floral identity genes that causes this homeotic
result, as opposed to a simple loss
of identity? Taking into account the origin of the floral meristem, what would be the
phenotype in a plant mutant in all
three classes of floral identity genes?
16. APETALA2 is a class "A" gene, while APETALA3 is a class "B" gene. Describe the
rationale behind naming both A
and B genes "apetala".
Cell Differentiation:
Define: Cell differentiation
Contrast differentiated cells with cancer cells. What aspects of cancer cells are targets for
anti-cancer treatments.
List three lines of experimental evidence that the effect of cell differentiation on the
nucleus is reversible.
Give examples of external and internal signals that regulate cell differentiation.
What are the defining characteristics of: myoblast, muscle fiber.
List the events that cause myoblasts to differentiate into muscle fibers.
Outline the strategy by which the myoD gene was shown to be a differentiation switch
for muscles.
Define: stem cell. What is a hematopoetic stem cell, and what controls its
differentiation.
Axon guidance:
List three potential functions of axon growth in the adult mammalian CNS.
Draw a cartoon of an axonal growth cone, label it (axon, filopodia, actin microfilaments,
microtubules), and describe the function of each structure/molecule.
Review Sperry’s eye rotation experiments in frogs. Draw a map of the axonal
connections between the retina and tectum. Why is this called a topographic map? What
is the evidence that retinal axons are guided to specific locations in the tectum?
Prenatal screening in humans: Dr. Slotnick.
Compare and contrast a screen with a diagnostic test.
What is the normal source of AFP (alpha fetoprotein)?
What are potential causes of elevated AFP? Abnormally low AFP?
Define: neural tube defect. What are potential causes?
What are external signs of a mild or hidden form of spinal bifida?
Describe the recommendation of folate in diet?
What is the effect of the age of the mother on trisomy 21?
Sex determination:
1. How is sex determined in humans?
2. What is the experimental evidence (in humans or animals) for the function of the SRY
gene?
3. List and describe the function of the hormones that regulate development of
reproductive organs.
4. What abnormalities or defects during development can lead to a lack of sexual
concordance at either the chromosomal, gonadal, or phenotypic level?
5. Define the freemartin condition in cattle. Explain the cause of freemartin
development in terms of hormonal regulation of reproductive development.
Define: male pseudo-hermaphrodite, Wolffian duct, Mullerian duct, sexual concordance.
Explain the androgen insensitivity syndrome.
Genetic engineering in mice:
List the experimental advantages of studying genes in mice.
Outline the steps in knocking out a mouse gene.
Contrast a knockout allele and a conditional knockout allele.
Describe the components of the Cre-lox system. How can it be used for conditional
alleles? Explain the term: inducible conditional allele.
Contrast hypomorphic and null alleles.
Gamete differentiation:
Define: gamete, haploid, diploid.
Keywords: Briefly compare and contrast the following pairs of terms. Check your
answer by using the glossary and the
text.
egg / oocyte
gamete / zygote
sex determination / sex differentiation
Wolffian duct / Müllerian duct
vas deferens / Fallopian tube
distal tip cell / spermatheca
germ cell / germ plasm
mitosis / meiosis
spermatogenesis / oogenesis
spermatogonia / spermatocyte
fertilization / polyspermy
acrosome reaction / cortical reaction
vitelline membrane / fertilization membrane
Factual recall questions:
1. In humans, an individual with an XXY chromosomal complement will develop as
(a) a male
(b) a female
(c) an hermaphrodite
(d) a super-female
(e) an individual with no secondary sexual characteristics
2. Müllerian-inhibiting substance
(a) causes the Müllerian ducts to develop into the oviducts
(b) causes the Müllerian ducts to develop into Wolffian ducts
(c) causes the Wolffian duct to develop into the vas deferens
(d) causes the testis to produce testosterone
(e) causes the Müllerian duct to regress by apoptosis in males
3. Mutations in the Drosophila sex-lethal gene
(a) are lethal to males, resulting in all female flies
(b) are lethal to all flies, once the sex of the individual begins to be expressed
(c) block female development, resulting in all male flies
(d) cause XY flies to develop as males
(e) promote female development of XY flies
4. In mammals, dosage compensation is carried out by
(a) decreasing the transcription of the X in males
(b) increasing the transcription of the X in males
(c) inactivating one X chromosome in females by condensation as heterochromatin
(d) inactivating one X chromosome in males by condensation as heterochromatin
(e) degrading one X chromosome in all female cells early in development
5. Germ cells are special in that
(a) they are the only cells that continue to divide in adults
(b) they are the only cells that undergo meiosis
(c) they are the only cells in the gonad
(d) they are the only diploid cells in most organisms
(e) they are the only cells that undergo mitosis
6. In mammals, formation of the egg involves arrest at what stage of meiosis?
(a) the primordial germ cell becomes arrested until ovulation
(b) the cell arrests as a primary oocyte, in prophase of the first meiotic division
(c) the cell arrests as a primary oocyte, in anaphase of the first meiotic division
(d) the cell arrests as a secondary oocyte, in metaphase of the second meiotic division,
until ovulation
(e) the cell arrests after completing meiosis, until it is ovulated
7. Fertilin is
(a) an enzyme packaged into the acrosome during sperm development
(b) a component of the zona pellucida that binds sperm and triggers the acrosome
reaction
(c) a sperm-bound ligand for ZP3
(d) a protein on the sperm head that mediates binding to the egg plasma membrane
(e) a protein released by the egg during the polyspermy block, after fertilization by the
initial sperm
Concept questions:
2. Summarize the evidence, from naturally occurring aneuploidies and translocations in
humans, that there are genes on
the Y chromosome that act dominantly to determine the sex of the individual. What is the
name of the one gene that seems to be the master regulator of sex determination? In the
absence of a Y chromosome, what sex results?
3. On what tissue does the Y chromosome initially act? How does the rest of the body
acquire sexual identity? What
molecule is the master regulator of somatic sexual differentiation? Describe some of the
observations that reveal the role
of hormones in sexual differentiation. Which sex is the default in mammals?
5. Contrast the origin of the germ cells with the origin of the somatic cells of the gonad.
12. Why does a chromosomal mechanism for sex determination lead to the need for
dosage compensation?
18. What is the embryological origin of the germ line in mice? What is the role of
migration in forming the gonads?
19. Contrast meiosis with mitosis. What features of meiosis are responsible for the
production of haploid products, as opposed to the diploid products that result from
mitosis?
20. At what developmental or adult stages do the meiotic cycles differ between sperm
and egg?
22. Outline the steps which ensue between the time a sperm first comes into contact with
the outer layers of the
mammalian egg and the time when the sperm head becomes internalized. Divide these
steps into 5 stages, following
Figure 12.22. Include the roles of hyaluronidase, the ZP3 receptor protein on the zona
pellucida, the acrosomal reaction,
and fertilin.
23. What are the blocks to polyspermy in mammalian eggs?
Define pronuclear fusion, and list the steps involved.