Chapter 18 Flashcards
Distinguish between the syncytial blastoderm stage and the cellular blastoderm stage in Drosophila embryogenesis.
The syncytial blastoderm is formed as nuclei migrate to the egg’s outer margin or cortex, where additional divisions take place.
Plasma membranes organize around each of the nuclei at the cortex, thus creating the cellular blastoderm.
What is meant by the term determination?
that a specific developmental fate for a cell is fixed in response to internal and external cues
Differentiation proceeds along the fated path after determination.
Which one of the following statements best describes the distinction between differentiation and determination during development?
Determination refers to early developmental and regulatory events by which cell fate is fixed.
Once fixed, differentiation is the manifestation of the determined state, in terms of genetic, physiological, and morphological changes.
Which one of the following statements does not describe zygotic genes?
They are gene products (mRNA and protein) encoded by genes in the mother’s genome that have their gene products placed in eggs.
The following statements describe zygotic genes:
They are activated or repressed depending on their response to maternal-effect gene products.
They contain 3 subsets genes including: gap genes, pair-rule genes, and segment polarity genes.
They divide the embryo into segments.
What is the phenotype associated with zygotic gene mutations?
embryonic lethality
Does the maternal genotype contain zygotic genes?
yes
What is the variable gene activity hypothesis?
The hypothesis states that all somatic cells in an organism contain equivalent genetic information, but the information is expressed differently in different cells.
Specific cell types in an organism are different because they have different patterns of gene expression.
All EXCEPT which of the following would be considered a good model of genetic organisms for studying development?
humans
Humans are not good model organisms for many reasons, such as the ethical issues surrounding experimentation.
All of the following are considered a good model of genetic organisms for studying development:
C. elegans
Drosophila
Arabidopsis
True or False?
Genetic involvement in development appears to be achieved, at least in part, by variable gene activity.
True
Which general genetic process is believed to account for the variety of cellular structures and functions in eukaryotic cells?
variable gene activity
What are maternal-effect genes?
genes transcribed in the mother that regulate expression of genes in the offspring
The products of maternal-effect genes are deposited in the egg and regulate the expression of zygotic genes.
Immediately after fertilization of a Drosophila egg, the zygote nucleus undergoes a series of divisions. Subsequent nuclear migration generates a(n) ________.
syncytial blastoderm
In Drosophila, maternal-effect genes are influential in determining the anterior-posterior organization of the developing embryo.
True
What are the 3 subsets of segmentation genes that divide the embryo into segments along the anterior-posterior axis?
gap, pair-rule, and segment polarity
Segmentation genes divide the embryo into a series of segments.
In Drosophila, the sequential order of the function of segmentation genes is ________.
gap, pair-rule, segment-polarity
Mutations that eliminate a contiguous region in the Drosophila embryo’s segmentation pattern are called ________.
gap genes
Which functions earlier in development: maternal-effect genes or zygotic genes?
maternal-effect genes
True or False?
Segmentation genes, such as the pair-rule class, are inherited through mitochondrial DNA in Drosophila.
False
The following 4 statements about pattern formation are true:
- Differential gene expression affects the developmental process in animals.
- Cells receive molecular signals that communicate their position in relation to other cells
- Homeotic genes code for transcription factors that control the development of segment-specific body parts.
- Positional information controls pattern formation.
Pattern formation is the development of a multicellular organism’s spatial organization, including the arrangement of tissues and organs.
Cells receive molecular signals, collectively called positional information, that inform the cells about their location in relation to other cells and to the body axes.
Positional information regulates pattern formation.
Homeotic genes are regulatory genes that work after the body axes have been established.
Homeotic genes identify particular body segments in an individual, eventually leading to the formation of segment-specific body structures in the correct locations on the body.
fly A, normal fly
wild type,
normal pattern formation,
normal Hox genes.
fly B, with legs on its head
abnormal pattern formation,
mutant Hox genes,
homeotic mutant
both fly A and fly B
produces transcription factors triggering gene expression for segment specific structures
Hox genes are a complex of homeotic genes that are expressed in a particular pattern along the anterior-posterior axis of many animals, including mice, birds, humans, and fruit flies (Drosophila).
The arrangement of Hox genes on a fruit fly chromosome correspond with expression of Hox genes in different body segments of a fruit fly embryo.
Hox genes code for transcription factors that are involved in the production of ______.
Hox genes code for transcription factors that are involved in the production of segment-specific structures.
The Hox genes of homeotic mutant fruit flies contain mutations resulting in abnormal pattern formation.
This often results in the formation of structures in the wrong location on the body—for example, legs where antennae are produced in wild-type (normal) fruit flies.
On which chromosome are the Drosophila Hox genes found?
chromosome 3
The Hox genes are found in two clusters on chromosome 3.
A gene that specifies the fate of a particular anatomical segment in Drosophila is called a(n) ________ gene.
homeotic selector
Which class of genes controls the developmental identity of segments along the anterior-posterior axis?
homeotic genes
Do Hox gene clusters exist in humans?
How many are known to exist?
yes, 4
Which of the following is a fundamental characteristic of the Notch pathway?
It works through direct cell to cell contact.
True or False?
Caenorhabditis elegans is extremely useful as an experimental organism because it has relatively few cells, and, for the most part, each embryonic cell’s fate is developmentally fixed.
True
In Drosophila development, the effects of BICOID protein vary along the axis of the embryo.
This is because _______.
there is an anterior to posterior gradient in BICOID protein concentration in the embryo
After fertilization, BICOID mRNA is translated and a concentration gradient of BICOID protein forms along the anterior-posterior axis of the embryo.
A set of known mutations in the BX-C genes in Drosophila results in the development of wings on a body segment that would not ordinarily have wings.
This is an example of mutation in which class of developmental genes?
Homeotic genes
Homeotic genes specify segment identity with respect to the body part that will develop at metamorphosis.
True or False?
Maternal effect genes are transcribed in the egg after fertilization.
False
Maternal effect genes are transcribed during oogenesis (in the mother).
The mRNA is translated in the embryo after fertilization.
Sepals are specified by expression of which of the following class or classes of homeotic genes?
class A
Petals are specified by expression of which of the following class or classes of homeotic genes?
class A class B
Stamens are specified by expression of which of the following class or classes of homeotic genes?
class B class C
Carpels are specified by expression of which of the following class or classes of homeotic genes?
class C
Which one of the following statements best describes the meaning of the term rescued in this context?
It’s when the introduction of a gene from an outside source restores the wild-type phenotype of the organism.
What do these results not indicate about the molecular nature of development?
They indicate that it is likely that all developmentally regulated mutant genes in Drosophila could be rescued by human or mouse homologs.
What do these results not indicate about the molecular nature of development?
They indicate that it is likely that all developmentally regulated mutant genes in Drosophila could be rescued by human or mouse homologs.
Specify adjacent broad regions of segments.
Gap Genes
Specify boundaries consisting of about 2 segments ride.
Pair-Rules Genes
Specify boundaries of all 14 segments and the orientation of each segment.
Segment Polarity
Mutations in the selector genes sometimes form structures in the wrong segment, transforming the antenna of a fly into a leg, for example. What are such mutations called?
homeotic mutations
True or False?
A homeobox gene is one that produces a group of repetitive base sequences such as a VNTR.
false
Which of the following statements about homeotic genes in Arabidopsis is FALSE?
Dozens of gene classes are involved in the production of floral organs.
This statement is false; only 3 gene classes (A, B, C) are responsible for setting up the pattern of a flower.
A number of genes that control expression of Hox genes in Drosophila have been identified. One of these homozygous mutants is extra sex combs, where some of the head and all of the thorax and abdominal segments develop as the last abdominal segment. In other words, all affected segments develop as posterior segments.
What does this phenotype tell you about which set of Hox genes is controlled by the extra sex combs gene?
This gene normally controls the expression of BX-C genes in all body segments.
How can you determine whether a particular gene is being transcribed in different cell types?
If protein products of a given gene are present in different cell types, it can likely be assumed that the gene is being transcribed.
In situ hybridization of a labeled probe that binds the transcript can be used to visualize transcript abundance in various cell types.
If polar cytoplasm is transplanted into the anterior end of the egg just after fertilization, which one of the following statements best describe what would likely happen to nuclei that migrate into this cytoplasm at the anterior pole?
Since the polar cytoplasm contains information to form germ cells, germ cells would form in the anterior region.
Which one of the following statements best describes maternal-effect genes?
They are gene products (mRNA and protein) encoded by genes in the mother’s genome that control early embryogenesis.
Which one of the following statements best describes when maternal-effect gene products are made?
They are made in early oocyte or nurse cells during oogenesis.
Which one of the following statements best describes what maternal-effect genes control?
They define early developmental events such as anterior-posterior polarity by having their gene products placed in eggs.
Which one of the following statements best describes the phenotype of maternal-effect mutations?
Female Drosophila homozygous for certain recessive maternal-effect mutations within their own genome are sterile.
