Chapter 22 - Developmental Genetics

Question 1

A geneticist has isolated a new mutation (m) in an egg-polarity gene of Drosophila. When two heterozygotes with this mutation (m/+) are crossed, it is expected that:
A. all female m/m offspring will die as embryos because they lack a necessary morphogen.
B. m/m offspring of either sex will die as embryos because they cannot set up one of the embryonic axes.
C. all the offspring will develop into adults but the m/m females will produce eggs that lack an mRNA needed for embryonic development.
D. all m/m offspring develop into adults but these adults will have two anterior ends.

Answer 1

C. all the offspring will develop into adults but the m/m females will produce eggs that lack an mRNA needed for embryonic development.

Question 2

Segmentation genes of the gap group:
A. are expressed in females during oogenesis and deposited in broad regions of the unfertilized egg.
B. are regulated by the gradients of bicoid and nanos proteins.
C. regulate the expression of the pair-rule segmentation genes.
D. All of the above.
E. Only B and C are correct.

Answer 2

E. Only B and C are correct.

Question 3

Mutations in the homeotic genes often cause:
A. the deletion of segments.
B. the absence of structures.
C. too many segments.
D. structures to appear in the wrong place.

Answer 3

D. structures to appear in the wrong place.

Question 4

Jr. Scientist is studying the disappearance of the tadpole’s tail during development. What is one characteristic that these dying tail cells should have?
A. Each cell will swell and burst.
B. The nucleus of each cell will get larger.
C. There will be an increase in caspase activity.
D. They will release cellular chemicals that trigger inflammation.
E. All of the above.

Answer 4

C. There will be an increase in caspase activity.

Question 5

The blindness of Mexican cave tetras resulted from __ expression of the __ (shh) gene and the __-__ __ (twhh) gene. Both of these genes __ transcription of other genes that leads to __ of lens cells.

Answer 5

increased; sonic hedgehog; tiggy-winkle hedgehog.

activate; apoptosis

Question 6

__ cells have the ability to develop into ANY cell type, even __-__ tissue. Plant and fungal cells often remain __.

__ cells have the ability to develop into ANY tissue.

Animal cells become committed to the development of a specific cell type in a process called __; this process often occurs after the first few cell __ of the __.

Answer 6

Totipotent; extra-embryonic.
totipotent.

Pluripotent.

determination; divisions; embryo

Question 7

Dolly proved that terminally __ mammalian cells __ all of their original __ information. As a result, scientists were able to conclude that development must require selective gene __.

Answer 7

differentiated; retain; genetic

expression.

Question 8

Why are clones are not genetically identical?

Answer 8

cytoplasmic genes come from the donor cell (?) and recipient egg.

Question 9

Drosophila development starts with an __, stages of __ development, stages of __ development, a __, and the adult stage.

Answer 9

egg; embryonic; larval; pupa

Question 10

In the initial stages of Drosophila, a multinucleate __ results from 9 nuclear divisions __ cell division. This is followed by a __ blastoderm where some nuclei migrate to the pole. These ‘pole’ nuclei later develop into __ cells (pole cells are are what’s engineered for __ transformation).

Answer 10

syncytium; without.

Syncytial.

germline; germline

Question 11

List the order and major role of Drosophila development and gene cascade.

Answer 11

egg-polarity (determination of major body axes)

gap genes (regional sections defined)

pair-rule genes (individual segments defined)

segment-polarity genes (polarity of individual segments defined)

homeotic genes (identity of individual segments defined).

Question 12

Egg-polarity genes are __ effect genes: the __ are in the egg prior to fertilization.

Answer 12

maternal; transcripts

Question 13

__ are transcription activators coded by developmental genes in Drosophila whose __ __ affect development of their surrounding regions.

Answer 13

Morphogens; concentration gradients

Question 14

__ proteins establish the dorsal-ventral axis in drosophila. This protein is normally distributed throughout the __ of an __ egg; after fertilization it is absorbed into the nuclei on the __ side. The protein is a __ that functions as a transcriptional __. High concentration leads to activation of the __ gene. Low concentration leads to activation of __ gene.

Answer 14

Dorsal.

cytoplasm; unfertilized; ventral (wtf).

morphogen; activator.

twist.
decapentaplegic.

Question 15

__ mRNA and protein establish the anterior portion of developing drosophila (the transcript is anchored by its _’ end to the __ of the egg; the protein forms a concentration __ with the highest __ at the anterior).
The protein is a __ that functions as a transcriptional __. High concentration leads to activation of the __ gene and __ protein which is needed for development of the head and thoracic structures.

Answer 15

Bicoid; 3’; anterior; gradient; concentration.

morphogen; activator.

hunchback; hunchback.

Question 16

__ mRNA establishes the posterior portion of developing drosophila. Upon fertilization, __ mRNA is translated, and __ proteins diffuse toward the anterior forming a concentration __.
The protein is a __ that __ translation of __ mRNA, thereby created a concentration gradient of __ protein. The concentration gradient of __ protein affects development of other structures.

Answer 16

Nanos.
nanos; nanos; gradient.

morphogen; represses; hunchback; hunchback.

hunchback

Question 17

In Drosophila, the expression of ~25 __ genes is controlled by the concentration gradients of __ and __ proteins. These __ genes fall into 3 classes: __ genes; __-rule genes; and __-polarity genes.

Answer 17

segment; bicoid; nanos.

segmentation; gap; pair-rule; segment-polarity.

Question 18

In Drosophila, __ genes function to establish the segmentation pattern including segments that define the __, that define the __, and that define the __.

Mutation of one __ gene, called __, causes the elimination of anterior segments.

Answer 18

gap; head, thorax, abdomen.

gap; Krüppel

Question 19

In Drosophila, __-__ genes function in development of pairs of segments.

Mutations of one of the __-__ genes, called __-__, causes the deletion of even-numbered segments. Mutations of the __ tarazu gene causes deletion of odd-numbered segments.

Answer 19

pair-rule;.

pair-rule; even-skipped.

fushi.

Question 20

In Drosophila, __-__ genes function in the development of polarity of each individual segment.

A mutation in one of the __-__ genes, called __, causes the posterior half of each segment to be replaced by a __ image of the __ half of an adjacent segment.

Answer 20

segment-polarity.

segment-polarity; gooseberry; mirror; anterior

Question 21

Mutations in __ gene cause legs to be formed where antennae should be; and mutations in __ leads to a second pair of __. Both are examples of __ genes.

__ genes are master __ genes that direct the development of particular body segments or structures (within a segment for Drosophila).

Answer 21

antennapedia; bithorax; wings.
Homeotic
Homeotic; regulator.

Question 22

In Drosophila, expression of homeotic genes is controlled by concentration gradient of the proteins encoded by segmentation genes including __, __-__, and __-__ genes. One example is Ultrabithorax (Ubx) whose activation is contingent on the concentration of __ protein (must fall within a specific range).

Answer 22

gap, pair-rule; segment-polarity

Hunchback

Question 23

Many homeotic genes contain a highly-conserved sequence called the __ that encodes for 60 amino acids. These amino acids form a __-__-__ domain common in DNA binding proteins.

The homeotic genes that contain a __ sequence are called __ genes for short.

Answer 23

homeobox.
helix-turn-helix

homeobox; hox

Question 24

__ genes are highly-conserved genes found in all animals including some plants and fungi. This finding suggests that __ genes developed early in the evolution of __ organisms

Answer 24

Hox.

Hox; eukaryotic.

Question 25

Mammalian __ gene homologs are similar in __ and occur in the same order (along the chromosome) as Drosophila __ genes.

Answer 25

Hox; sequence; homeotic

Question 26

During apoptosis, a series of proteins called __ cleave other proteins at specific sites (the __ step). Cleavage of an inactive __ leads to activation and degradation of the cells __ and eventual death.

Answer 26

caspases; initiation.

DNAse; nucleus/genome.

Question 27

Apoptosis can be triggered by __ (enzyme), or by infection of a __, or __ damage.

Answer 27

caspases; virus; mitochondrial

Question 28

Some stages in development require removal of excess cells by __ (e.g. __ between the fingers of human embryos).

Some diseases are affected by __ or __ of __.

Answer 28

apoptosis; webbing.

excessive; absence; apoptosis

Question 29

Eyeless gene in Drosophila is a mutated gene that causes the formation of a small eye. In 1993, Gehring sought to prove that eyeless encoded a transcription factor, so he engineered a transgene to turn eyeless “on” where it is normally off. Doing so demonstrated what?

Answer 29

that eyeless encodes a master regulator for development

Question 30

__-__ is the study of evolution through developmental pathways. One such gene studied is eyeless in Drosophila who shares counterparts with mice (called __ eye) and humans (called __). Similarities between these genes strongly suggests evolution from the __ __ __ of these species.

Answer 30

Evo-devo.

small; Aniridia.

last common ancestor

Question 31

Antibody diversity is achieved via __ __. Genes encoding the heavy and light chains are composed of 3 segments: __ region, __ region, and the constant region.

Answer 31

somatic recombination.

variable; joining.

Question 32

Somatic __ cells give rise to B-cells. Somatic __ leads to deletions of __ and __-__ DNA segments, and these deletions are responsible for genetic __ of B-cells.

Pre-mRNA of these B-cells have one __ region, several __ regions, and one __ region. The pre-mRNA is __ to yield mature mRNA; and translation produces a unique __ light chain.

Answer 32

germline.
recombination; variable; joining-region; diversity.

variable; joining; constant.
spliced; kappa

Question 33

During somatic recombination, variability is created based on which __-__ segments were deleted during recombination, and which of the remaining segments lies immediately upstream of the __-__ segments.

Answer 33

variable-region; joining-region

Question 34

Patches of tissue in the body of the Drosophila larvae that develop into specific adult body parts during metamorphosis are called
A. Pupation disks. 
B. Homeotic disks. 
C. Imaginal disks. 
D. Homeotic genes. 
E. Imaginal genes.

Answer 34

C. Imaginal disks.

Question 35

Which of the following is false regarding morphogens?
A. Establish chemical gradients that affect gene expression in specific regions of the
developing embryo.
B. Often function as transcriptional activators.
C. Are found in the sperm prior to fertilization.
D. Play critical roles in establishing body pattern formation during early development of the embryo.
E. Select this answer if more than one of the choices A-D are false

Answer 35

C. Are found in the sperm prior to fertilization.

Question 36

Which of the following is true about the cytoplasm of an animal oocyte?
A. It stores molecules needed for support of the earliest cleavage divisions.
B. It stores molecules needed for RNA synthesis.
C. It stores molecules needed for protein synthesis.
D. It organizes molecules in the cytoplasm to provide positional information.
E. More than one of the above answers are true

Answer 36

E. More than one of the above answers are true

Question 37

A blastula is
A. A stage in embryonic development characterized by cell migration.
B. An unfertilized egg.
C. A ball of approximately 10⁴ cells containing a cavity.
D. A fertilized egg that has not undergone the first cleavage division.
E. None of the above.

Answer 37

C. A ball of approximately 10⁴ cells containing a cavity.

Question 38

Egg-polarity genes in Drosophila establish the main __ __.

Answer 38

body axes

Question 39

Segmentation genes determine the __ and __ of body segments

Answer 39

number; orientation

Question 40

Homeotic genes establish the __ of each segment.

Answer 40

identity