Deck 20: Developmental Genetics

Question 1

Suppose that a homeotic gene from Drosophila is introduced into an Arabidopsis embryo with a mutation in one of its homeotic flower genes.What effect would you expect and why?

A)rescue (or negating)of the phenotype of the mutant because the fly Hox gene supplies the missing protein
B)correction of the sequence in the mutant by recombination with the Drosophila gene sequence
C)expression of the Drosophila homeotic gene correcting the mRNA of the mutant plant
D)a mixture of roughly equal numbers of Drosophila and plant gene product,producing an intermediate phenotype
E)no effect,because Hox genes are different from MADS box genes

Answer 1

E

Question 2

In early vertebrate embryonic development,a number of pathways,such as Wnt,Hedgehog,and Notch,regulate differentiation and organ formation.They operate by

A)formation of new transcription factors at each stage.
B)transcription activation due to interaction among transcription factors.
C)cell signaling mediated by receptor binding.
D)establishing anterior-posterior and dorsal-ventral symmetry.
E)stimulating MADS box genes.

Answer 2

C

Question 3

Since mice embryos with loss-of-function Hox mutations result in homeotic alterations,then introduction of such a mutation might cause

A)ribs on normally rib-less vertebrae.
B)pointed rather than rounded ears.
C)a change in fur coloration along the dorsal midline.
D)behavioral alterations causing limb shaking.
E)paralysis of hindlimbs but not forelimbs.

Answer 3

A

Question 4

In Drosophila,a developmental mutation called ssᵃ (spineless aristapedia)results in flies with mini leg parts on the antennae.What kind of gene is this mutation?

A)gap gene
B)pair-rule gene
C)homeotic gene
D)segment polarity gene
E)maternal effect gene

Question 5

Segmentation genes in Drosophila act in which of the following orders?

A)segmental,helical,spherical
B)pair-rule,transdeterminal,gap genes
C)gap,pair-rule,segment polarity
D)pair-rule,segment polarity,gap genes
E)pair-rule,segment polarity,Hox genes

Question 6

An Antennapedia (Antp)mutant in Drosophila has legs in place of antennae.This is caused by

A)activation of the Antp gene in the head region instead of in the thorax.
B)the product of an abdominal segment gene being expressed in the head.
C)a chromosomal error that shifts this Antp gene to the anterior end of the complex.
D)the interaction of an inhibitor gene of the bithorax complex with the Antp mutation.
E)loss of function of the Antp gene.

Question 7

Human Hox genes are in four clusters: HOXA,HOXB,HOXC,and HOXD,for a total of 39 genes.Besides conserving the clustering of genes,evolution has also conserved

A)their chromosomal locations.
B)the order of the genes within them.
C)their expression along the dorsal-ventral axis.
D)the mutations to which they give rise.
E)their bilateral symmetry.

Question 8

Holoprosencephaly is a highly variable condition in mammals,including humans.Its effects range from an absence of brain areas,mid-face disorders,and cyclopia to slight dental abnormalities.One form,HPE3,is caused by Shh mutations.Familial cases are inherited as dominants.Which of the following do you expect?

A)HPE3 is actually a multigene complex.
B)Each type of malformation is due to a different HPE3 allele.
C)HPE3 expression is modified by genetic background.
D)HPE3 individuals also share a common environmental exposure.
E)All mutations in Shh that result in HPE3 are due to frameshifts.

Question 9

Polycomb group (PcG)mutants cause gain-of-function of Antennapedia (Antp)and other homeotic genes by causing some of these genes to be expressed in tissues where they are usually repressed.PcG has a domain that binds to methylated histone H3.This finding supports which of the following hypotheses?

A)that PcG binds to Antp genes and serves as a transcription activator
B)that PcG mutants have phenotypes like those of Antp mutants
C)that PcG regulates genes by altering chromatin remodeling
D)that PcG initiates repression of Antp genes in tissues
E)that PcG is a repressor molecule like those found in bacteria

Question 10

A pair-rule gene in Drosophila called runt controls some of sex and nervous system formation.In the mouse,runt controls blood cell formation,osteogenesis,and genital structures.In humans,the analog of runt,when mutated,causes children to lack collar bones,and the opening at the top of the skull fails to close.What kind of experiment could tell you whether these genes are conserved in function?

A)sequencing of the runt genes from each of the three species of organisms
B)in vivo experiments inserting the copy of the moue gene into a segmented fly embryo
C)in vitro experiment that inserts mouse runt gene into cells from an unsegmented Drosophila embryo
D)sequencing the proteins encoded for by each of the species' runt genes
E)use of immunological methods to identify the target cells of the species' runt transcription factors

Question 11

The abdominal segments of Drosophila have no appendages.Loss of function of bithorax genes results in appendages forming in these abdominal segments.Therefore,

A)bithorax mutations are necessarily recessive.
B)bithorax genes normally activate appendage-forming genes.
C)ultrabithorax usually acts to oppose bithorax genes.
D)bithorax normally activates a gene that negatively regulates appendages in the abdomen.
E)expression of bithorax wild-type genes suppresses all appendage formation.

Question 12

There is much controversy in the newsboth scientific and popularabout the use of embryonic stem cells for research.These cells are grown as cell lines in culture,created by taking the inner cell mass from 5-day-old embryos.What is the center of the controversy?

A)the fact that the embryos are mostly those unused by in vitro clinics
B)the knowledge that these cell lines have reverted spinal cord injuries in mice
C)the unproven usefulness of stem cells to treat human disorders
D)the realization that these cells are pluripotent rather than totipotent
E)the difference of opinion about whether these embryos are persons

Question 13

Aniridia is a human condition in which the eye has no iris.The protein encoded by the gene responsible for aniridia is very nearly identical to the protein product of the fly Eyeless protein.What experiment could provide evidence that the two genes are functionally equivalent?

A)Introduce the aniridia mutation into Drosophila embryos to look for iris formation.
B)Sequence the Eyeless and aniridia DNA sequences and regulators.
C)Use the Eyeless mRNA as a probe in other invertebrate and non-mammalian species.
D)Introduce the mouse wild-type sequence into the fly egg to see whether mouse eyes develop.
E)Introduce the mouse aniridia wild-type sequence into the fly to see whether fly eyes develop.

Question 14

Mutations of regulatory elements of developmental genes may have either dominant or recessive effects.If a mutation results in a silencer element,that negatively regulates,which do you expect?

A)a recessive effect in which cis elements are up-regulated
B)a recessive effect in which cis elements are down-regulated
C)a dominant effect in which the silencer down-regulates gene activity
D)a dominant effect in which gene activity is up-regulated
E)a dominant effect in which the silencer is transactivating

Question 15

As a Drosophila larva molts and becomes a pupa,most of the larval tissues die and adult structures are formed from cells in clusters known as imaginal discs that have remained unchanged throughout the larval stages.Therefore,the disc cells are

A)maternal.
B)zygotic.
C)embryonal.
D)differentiated.
E)transcriptionally activated.

Question 16

Drosophila mutations such as bcd,if homozygous in the mother,produce offspring with lethal defects,no matter what the genotype of the offspring.For some other genes,the mutant phenotype can be "rescued" by introducing a wild-type allele.Why the difference?

A)Non-rescuable mutations are of paternal origin.
B)Rescuable mutations act as dominants.
C)bcd is a maternal effect mutation.
D)Rescue requires recombination between the maternal and introduced alleles.
E)bcd is a Hox gene.

Question 17

Use of double mutants has been invaluable in studying developmental pathways.In C.elegans,sex is determined by the ratio of sets of autosomes to X chromosomes.A diploid male has one X,and diploid hermaphrodites have two X's.The loss-of-function gene her-1 produces XO worms that are hermaphrodites,but XX worms are unaffected.Mutation of a second gene,tra,causes the XX to develop as male.Given this information,what would be the phenotype of a tra,her-1 double mutant?

A)a male nematode
B)a female nematode
C)a hermaphrodite
D)an intersex variant
E)lethality

Question 18

A homeotic mutant flower has an arrangement (from outside in)of carpels,stamens,stamens,carpels instead of the usual sepal,petals,stamens,carpels.In general,Class A genes specify sepals,Class A and B genes specify petals,Class B and C genes specify stamens,and Class C specifies carpels.This mutant must therefore have a mutation in

A)a Class A gene.
B)a Class B gene.
C)a Class C gene.
D)both A and B.
E)both B and C.

Question 19

In Drosophila,germ cells develop from pole nuclei isolated from the rest of the embryo at the posterior end.How are they "protected" from the effects of posterior concentrations of zygote-produced mRNAs and proteins?

A)Their genes have unresponsive promoters.
B)The cytoplasm at the pole is separated by a compartmentalizing membrane.
C)The pair-rule,gap,and segmentation genes are not expressed in these cells.
D)Homeotic genes in these cells are inhibited by zygotic genes from the mother.
E)Paternal effects operate on the embryo only in the pole cells.

Question 20

In an organism such as a sea urchin,administration of actinomycin D prevents RNA synthesis.However,early development up to gastrula formation can take place in the presence of actinomycin D but gastrulation cannot.This implies that

A)development beyond gastrulation requires actD.
B)actD is part of the normal environment of a sea urchin and serves as a developmental signal molecule.
C)actD receptors begin to form only on cell surfaces of the gastrula.
D)maternal effect genes regulate development until gastrulation.
E)immature sea urchin embryos produce actD to regulate further development.

Question 21

Cell signaling during much of C.elegans development occurs along concentration gradients.What kind of signaling does this represent?

Question 22

The maternal effect bicoid protein is a transcription factor that binds to the promoter of a zygotic gene to activate its expression.What is this second gene?

Question 23

A highly conserved protein domain of 60 amino acids is found in a large number of animals.This domain allows the proteins in question to bind to what?

Question 24

Certain species of lilies,if eaten by pregnant ewes,can cause the ewes to produce lambs with severe birth defects because the plants' cyclopamine can block embryonic response to Shh.This type of birth defect is a phenocopy of mutations in which genes?

Question 25

Cell autonomous genes affect only those cells in which they are expressed.Which group of early developmental genes are not cell autonomous?

Question 26

In Drosophila and other animals,Hox genes encode transcription factors that control development;but in Arabidopsis,a different family of transcription factors is produced with a different set of conserved amino acids.These are encoded by what group of genes?

Question 27

What characteristic of a cellular blastoderm in Drosophila embryogenesis distinguishes it from the syncytial blastoderm?

Question 28

Certain mutations in non-Hox genes actually produce homeotic mutants due to a failure to modulate chromatin acetylation appropriately.This influence on cellular "memory" is called what?

Question 29

During the evolution of development in animals,it is found that many regulatory genes have been co-opted for the development of different structures,such as limbs or digits.This is an example of what current area of research?

Question 30

Which of the groups of early developmental genes in Drosophila act across segment boundaries to produce parasegments?

Question 31

Mouse eye genes can be inserted into Drosophila and can regulate the flies' eye formation.Differences in size and shape of a zebra are controlled by a gene also found in zebrafish.What do these examples illustrate?

Question 32

The Antennapedia complex and the bithorax complex of genes all encode transcription factors have a 180-bp DNA-binding domain.What is this domain called?

Question 33

The establishment of the axes of the body plan occurs during which stage of Drosophila development?

Question 34

In the development of C.elegans,an embryo of 1090 cells then loses 131 cells.This is an example of what process?

Question 35

Which structure in plants acts most like embryonic stem cells in animals?

Question 36

In Arabidopsis thaliana,a model organism in plant genetics,there are three classes of genes that control the development of floral structures: A,B,and C.Mutations of these genes cause organs to form in inappropriate places.What category of genes are they?

Question 37

Which group of genes in Drosophila embryos must be mutated if the result is elimination of a significantly sized,contiguous region of segmentation?

Question 38

Homeotic genes in virtually all animals are said to show colinearity between the spatial arrangement of the tissues they act on as well as what other feature?

Question 39

An embryonic stem cell has the potential to differentiate into any cell or tissue type.Is it differentiated,pluripotent,or totipotent?

Question 40

If a cell from the blastoderm of the Drosophila embryo is committed to form part of an abdominal segment of the adult,such as the sixth one,and this cell is transplanted into the thorax-committed region of another embryo,will it develop properties of a thoracic or an abdominal segment?

Question 41

Use a description of C.elegans development to distinguish clearly between differentiation and determination.

Question 42

How and when does the Antennapedia complex change antennae into legs?

Question 43

The process by which the presence and activity of neighboring cells determine an aspect of development is called ________.

Question 44

What genetic evidence can demonstrate that some developmental events are due to chemical signaling?

Question 45

In some forms of cancer,the expression of certain homeotic genes has been altered.Is this more likely to be a cause or an effect of the cancer? Explain.

Question 46

What are Hox and MADS genes,and what do they have in common?

Question 47

Most of the genes controlling development encode either signal molecules or ________.

Question 48

A mutation in a fly causes an antenna to develop where a leg should be.This is an example of a ________ mutation.

Question 49

Coordinate genes in an organism such as Drosophila determine the ________ of the early embryo.

Question 50

Molecules whose concentration and position in an embryo determine some aspect of development are called ________.