Transcript Wednesday, September 5

21.1 – 1
As you learned in chapter 12, mitosis
gives rise to two daughter cells that are
genetically identical to the parent cell.
Yet you, the product of many mitotic
divisions, are not just a ball of identical
cells. Why?
21.1 – 1
Cells undergo differentiation
during embryonic development,
becoming different from each
other; in the adult organism,
there are many highly specialized
cell types.
21.1 – 2
What are the fundamental
differences between plants and
animals in their mechanisms of
development?
21.1 – 2
During animal development,
movement of cells and tissues is a
major mechanism, which is not the
case in plants. In plants, growth
and morphogenesis continue
throughout the life of the plant.
This is true only of a few types of
animal cells.
21.2 – 1
Why can’t a single embryonic stem
cell develop into an embryo?
21.2 – 1
Information deposited by the mother
in the egg (cytoplasmic determinants)
is required for embryonic
development.
21.2 – 2
If you clone a carrot, will all the progeny
plants (“clones”) look identical? Why or
why not?
21.2 – 2
No, primarily because of the subtle
(and not-so-subtle) differences in
their environments.
21.2 – 3
The signal molecules released by an
embryonic cell can induce changes in a
neighboring cell without entering the
cell. How?
21.2 – 3
By binding to a receptor on the
receiving cell’s surface and triggering
a signal transduction pathway that
affects gene expression.
21.3 – 1
Why are fruit fly maternal effect genes
also called egg-polarity genes?
21.3 – 1
Because their products, made by the
mother, determine the head and tail
ends, as well as the back and belly, of
the egg (and eventually the adult fly).
21.3 – 2
If a researcher removes the anchor cell
from a C. elegans embryo, the vulva
does not form, even though all the cells
that would have made the vulva are
present. Explain why.
21.3 – 2
The prospective vulval cells require
an inductive signal from the anchor
cell before they can differentiate
into vulval cells.
21.3 – 3
Explain why cutting and rooting a shoot
from a plant, then planting it
successfully, provides evidence that
plant cells are totipotent.
21.3 – 3
A shoot is a differentiated
structure, yet some of the cells that
make it up are able to differentiate
and redifferentiate, forming all of
the organs of the new plant.
21.4 – 1
The DNA sequences called
homeoboxes, which help homeotic
genes in animals direct development,
are common to flies and mice. Given
this similarity, explain why these
animals are so different.
21.4 – 1
Homeotic genes differ in their
nonhomeobox sequences, which
determine their interactions with
other transcription factors and
hence which genes are regulated by
the homeotic genes. These
interactions differ in the two
organisms, as do the expression
patterns of the homeobox genes.