Chapter 16. Genes and Development Notes
AP Biology Mrs. Laux
I. Development-the process by which the descendants of a single cell
specialize and organize into a complex organism
A. 3 Phases
1. Cell division
2. Cell determination-the process of gradual commitment to
specific patterns of gene activity
a. Differential Gene Expression-process of
developmental gene regulation
i. most occurs at transcriptional level
-either activated or repressed
-commitment restricts development to
limited set of final tissue types
ii. if always activated-regulated by quantity
iii. causes differences among cell types
3. Cell differentiation-final step in cell specialization
a. more than 200 different kinds of cells in humans
b. each makes highly specific set of proteins
-ex: RBCs-hemoglobin-90% of total mass
-ex: all cells have enzymes for glycolysis
c. last stage in developmental process
-cells become structurally and functionally
recognized
-ex: bone cells, nerve cells
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Chapter 16. Genes and Development Notes
AP Biology Mrs. Laux
B. Genetic Potential
1. Nuclear Equivalence
a. nuclei of essentially all differentiated adult cells of an
individual are genetically (though not necessarily
metabolically) identical to each other
b. identical to nucleus of fertilized egg (zygote) cell from
which they descended
c.. virtually all somatic cells (cells of the body)
2. Totipotency
a. nucleus contains all info required to direct normal
development
b. tissue culture experiment with carrots
i. root cells induced to divideÆembyroid bodies
developedÆgrew into carrot (plantlets)
ii. new organism was clone-genetically alike
3. Stem cells
a. Stem cells divide to produce differentiated
descendants
b. divide to maintain stem cell population
c. Totipotent stem cells
i. give rise to all body cell types and placenta
d. Pluripotent stem cells
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Chapter 16. Genes and Development Notes
AP Biology Mrs. Laux
i. give rise to many, but not all, cell types
e. Embryonic stem cells
i. Form when zygote cells divide
(a.) come from 5- or 6-day-old blastocyst
(b.) are pluripotent
(c.) can develop into any type of body cell
ii. are not totipotent
(a.) because cannot form cells of placenta
f. Adult stem cells
i. Found in human brain, retina, heart, bone
marrow, dental pulp, intestines, other sites
i. are pluripotent
(a.) differentiation more limited than ES
cells
*Note: keep these distinguished from germ-line cells, which undergo
meiosis and give rise to gametes; set aside early in development
II. Morphogenesis-the development of form
A. Multi-step process called pattern formation
1. Cells in specific locations become progressively organized
into recognizable structures
2. Know a lot from D. melanogaster
III. Drosophila melanogaster Research
A. Advantages
1. Abundance of mutations
a. affect organism’s segmented body plan
2. Developmental genes in fruit flies
a. important in growth and development of all animals
3. Polytene (many-stranded) chromosomes
a. unusual interphase chromosomes that form when
DNA replicates without mitosis and cytokinesis
b. puffs-sites of intense gene activity
c. constant in a particular tissue
-show areas of mutation
d. paired and consist of more than a 1000 parallel
longitudinal DNA fibers
e. can clone through chromosome walking
B. Life Cycle
1. sperm and eggÆzygoteÆlarvaÆseveral
moltsÆpupaÆmetamorphosisÆadult fliesÆsperm and egg…
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Chapter 16. Genes and Development Notes
AP Biology Mrs. Laux
2. Imaginal discs
a. precursor cells of adult structures in larva
b. In metamorphosis, within the body of the
caterpillar begin to crop up They aren't recognized by
the immune system as normal so the caterpillar's
immune system wipes them out as they pop up.
c. It isn't until they begin to link forces and join up with
each other that they get stronger and are able to resist
the onslaught of the immune system, until the immune
system itself breaks down and the imaginal cells form
the body of the butterfly.
d. Imaginal cells are tissue-specific progenitors
allocated in embryogenesis that remain quiescent
during embryonic and larval life. During Drosophila
metamorphosis, most larval cells die. Pupal and adult
tissues form from imaginal cells.
3. Hox genes
a. a group of related genes that specify the anteriorposterior axis and segment identity of metazoan
organisms during early embryonic development.
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Chapter 16. Genes and Development Notes
AP Biology Mrs. Laux
b. are critical for the proper number and placement of
embryonic segment structures (such as legs, antennae,
and eyes).
3. Maternal effect genes
a. encode for specific mRNA molecules that are involved
in establishing the polarity of embryo
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Chapter 16. Genes and Development Notes
AP Biology Mrs. Laux
4. Segmentation genes
a. Generate repeating pattern of body segments in
embryo
5. Gap genes
a.organize anterior, middle, posterior regions
6.Pair-rule genes, segment polarity genes
a. affect all segments
7. Homeotic genes
a. Specify identity of each segment
i. later-acting
ii. are involved in developmental patterns and
sequences. For example, homeotic genes are
involved in determining where, when, and how
body segments develop in flies.
iii. Alterations in these genes cause changes in
patterns of body parts, sometimes causing
dramatic effects such as legs growing in place of
antennae
b. The study of imaginal discs in the fruit fly
Drosophila melanogaster led to the discovery of
homeotic mutations such as antennapedia, where
the developmental fate of a disc could sometimes
change.
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Chapter 16. Genes and Development Notes
AP Biology Mrs. Laux
c. Study of this phenomenon led to the discovery of the
homeobox genes, and started a revolution in the
understanding of development in multi-celled animals
that is still underway.
IV. Apoptosis
A. Programmed cell death
1. In human development
a. hand forms as a webbed structure
b. fingers separate when cells between them die
partial simple syndactyly
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