Chapter 18

Question 1

Distinguish between the syncytial blastoderm stage and the cellular blastoderm stage in Drosophila embryogenesis.

Answer 1

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.

Question 2

What is meant by the term determination?

Answer 2

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.

Question 3

Which one of the following statements best describes the distinction between differentiation and determination during development?

Answer 3

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.

Question 4

Which one of the following statements does not describe zygotic genes?

Answer 4

They are gene products (mRNA and protein) encoded by genes in the mother’s genome that have their gene products placed in eggs.

Question 5

The following statements describe zygotic genes:

Answer 5

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.

Question 6

What is the phenotype associated with zygotic gene mutations?

Answer 6

embryonic lethality

Question 7

Does the maternal genotype contain zygotic genes?

Answer 7

yes

Question 8

What is the variable gene activity hypothesis?

Answer 8

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.

Question 9

All EXCEPT which of the following would be considered a good model of genetic organisms for studying development?

Answer 9

humans

Humans are not good model organisms for many reasons, such as the ethical issues surrounding experimentation.

Question 10

All of the following are considered a good model of genetic organisms for studying development:

Answer 10

C. elegans
Drosophila
Arabidopsis

Question 11

True or False?

Genetic involvement in development appears to be achieved, at least in part, by variable gene activity.

Answer 11

True

Question 12

Which general genetic process is believed to account for the variety of cellular structures and functions in eukaryotic cells?

Answer 12

variable gene activity

Question 13

What are maternal-effect genes?

Answer 13

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.

Question 14

Immediately after fertilization of a Drosophila egg, the zygote nucleus undergoes a series of divisions. Subsequent nuclear migration generates a(n) ________.

Answer 14

syncytial blastoderm

Question 15

In Drosophila, maternal-effect genes are influential in determining the anterior-posterior organization of the developing embryo.

Answer 15

True

Question 16

What are the 3 subsets of segmentation genes that divide the embryo into segments along the anterior-posterior axis?

Answer 16

gap, pair-rule, and segment polarity

Segmentation genes divide the embryo into a series of segments.

Question 17

In Drosophila, the sequential order of the function of segmentation genes is ________.

Answer 17

gap, pair-rule, segment-polarity

Question 18

Mutations that eliminate a contiguous region in the Drosophila embryo’s segmentation pattern are called ________.

Answer 18

gap genes

Question 19

Which functions earlier in development: maternal-effect genes or zygotic genes?

Answer 19

maternal-effect genes

Question 20

True or False?

Segmentation genes, such as the pair-rule class, are inherited through mitochondrial DNA in Drosophila.

Answer 20

False

Question 21

The following 4 statements about pattern formation are true:

Answer 21

• 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.

Question 22

Pattern formation is the development of a multicellular organism’s spatial organization, including the arrangement of tissues and organs.

Answer 22

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.

Question 23

Homeotic genes are regulatory genes that work after the body axes have been established.

Answer 23

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.

Question 24

fly A, normal fly

Answer 24

wild type,
normal pattern formation,
normal Hox genes.

Question 25

fly B, with legs on its head

Answer 25

abnormal pattern formation, mutant Hox genes, homeotic mutant

Question 26

both fly A and fly B

Answer 26

produces transcription factors triggering gene expression for segment specific structures

Question 27

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).

Answer 27

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.

Question 28

Hox genes code for transcription factors that are involved in the production of ______.

Answer 28

Hox genes code for transcription factors that are involved in the production of segment-specific structures.

Question 29

The Hox genes of homeotic mutant fruit flies contain mutations resulting in abnormal pattern formation.

Answer 29

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.

Question 30

On which chromosome are the Drosophila Hox genes found?

Answer 30

chromosome 3 The Hox genes are found in two clusters on chromosome 3.

Question 31

A gene that specifies the fate of a particular anatomical segment in Drosophila is called a(n) ________ gene.

Answer 31

homeotic selector

Question 32

Which class of genes controls the developmental identity of segments along the anterior-posterior axis?

Answer 32

homeotic genes

Question 33

Do Hox gene clusters exist in humans? How many are known to exist?

Answer 33

yes, 4

Question 34

Which of the following is a fundamental characteristic of the Notch pathway?

Answer 34

It works through direct cell to cell contact.

Question 35

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.

Answer 35

True

Question 36

In Drosophila development, the effects of BICOID protein vary along the axis of the embryo. This is because _______.

Answer 36

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.

Question 37

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?

Answer 37

Homeotic genes Homeotic genes specify segment identity with respect to the body part that will develop at metamorphosis.

Question 38

True or False? Maternal effect genes are transcribed in the egg after fertilization.

Answer 38

False Maternal effect genes are transcribed during oogenesis (in the mother). The mRNA is translated in the embryo after fertilization.

Question 39

Sepals are specified by expression of which of the following class or classes of homeotic genes?

Answer 39

class A

Question 40

Petals are specified by expression of which of the following class or classes of homeotic genes?

Answer 40

``` class A class B ```

Question 41

Stamens are specified by expression of which of the following class or classes of homeotic genes?

Answer 41

``` class B class C ```

Question 42

Carpels are specified by expression of which of the following class or classes of homeotic genes?

Answer 42

class C

Question 43

Which one of the following statements best describes the meaning of the term rescued in this context?

Answer 43

It’s when the introduction of a gene from an outside source restores the wild-type phenotype of the organism.

Question 44

What do these results not indicate about the molecular nature of development?

Answer 44

They indicate that it is likely that all developmentally regulated mutant genes in Drosophila could be rescued by human or mouse homologs.

Question 45

What do these results not indicate about the molecular nature of development?

Answer 45

They indicate that it is likely that all developmentally regulated mutant genes in Drosophila could be rescued by human or mouse homologs.

Question 46

Specify adjacent broad regions of segments.

Answer 46

Gap Genes

Question 47

Specify boundaries consisting of about 2 segments ride.

Answer 47

Pair-Rules Genes

Question 48

Specify boundaries of all 14 segments and the orientation of each segment.

Answer 48

Segment Polarity

Question 49

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?

Answer 49

homeotic mutations

Question 50

True or False? A homeobox gene is one that produces a group of repetitive base sequences such as a VNTR.

Answer 50

false

Question 51

Which of the following statements about homeotic genes in Arabidopsis is FALSE?

Answer 51

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.

Question 52

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?

Answer 52

This gene normally controls the expression of BX-C genes in all body segments.

Question 53

How can you determine whether a particular gene is being transcribed in different cell types?

Answer 53

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.

Question 54

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?

Answer 54

Since the polar cytoplasm contains information to form germ cells, germ cells would form in the anterior region.

Question 55

Which one of the following statements best describes maternal-effect genes?

Answer 55

They are gene products (mRNA and protein) encoded by genes in the mother’s genome that control early embryogenesis.

Question 56

Which one of the following statements best describes when maternal-effect gene products are made?

Answer 56

They are made in early oocyte or nurse cells during oogenesis.

Question 57

Which one of the following statements best describes what maternal-effect genes control?

Answer 57

They define early developmental events such as anterior-posterior polarity by having their gene products placed in eggs.

Question 58

Which one of the following statements best describes the phenotype of maternal-effect mutations?

Answer 58

Female Drosophila homozygous for certain recessive maternal-effect mutations within their own genome are sterile.