Question 1

Which of the following best explains why Caenorhabditis elegans is a powerful model organism for studying developmental genetics?

Accepted Answer

Its transparent body and invariant cell lineage allow direct observation of cell fate and division.

Question 2

In Experiment 26A, C. elegans mutants with the 'bag of worms' phenotype were used to study developmental timing. What type of mutation is primarily responsible for the extended T-cell lineage observed in the n355 strain?

Accepted Answer

A gain-of-function mutation causing persistent lin-14 expression

Question 3

Which of the following statements about homeotic genes in vertebrates is correct?

Accepted Answer

The arrangement of Hox genes on the chromosome corresponds to their expression domains along the anterior-posterior axis.

Question 4

A researcher observes that in a mutant mouse, HoxC-6 expression begins at vertebra 5 instead of vertebra 8. What is the most likely anatomical consequence?

Accepted Answer

The mouse will have a shorter neck region.

Question 5

Which of the following best describes the role of the MyoD protein in vertebrate development?

Accepted Answer

It is a transcription factor with a bHLH domain that initiates skeletal muscle differentiation.

Question 6

Which of the following scenarios would most likely result from a loss-of-function mutation in the CLV3 gene in Arabidopsis?

Accepted Answer

The organizing center would expand, causing overproduction of undifferentiated stem cells.

Question 7

In the ABC model of flower development, which combination of gene activities is required for the formation of stamens?

Accepted Answer

B + C + SEP

Question 8

A triple mutant Arabidopsis flower lacking all SEP genes produces only sepals in all four whorls. What does this observation suggest about the function of SEP genes?

Accepted Answer

SEP genes are required for the formation of petals, stamens, and carpels, but not sepals.

Question 9

Which of the following is a key difference between plant and animal development at the cellular level?

Accepted Answer

Most plant cells are totipotent and can regenerate a whole organism.

Question 10

A C. elegans mutant with a loss-of-function allele of lin-14 (such as n540) exhibits which of the following T-cell lineage patterns?

Accepted Answer

The L1 pattern is skipped, and cells adopt later-stage fates prematurely.

Question 11

Which of the following best describes the regulatory interaction between WUS and CLV3 in the shoot meristem of Arabidopsis?

Accepted Answer

WUS activates CLV3, and CLV3 restricts WUS expression to the organizing center.

Question 12

Which of the following statements about the molecular nature of plant homeotic genes is correct?

Accepted Answer

Plant homeotic genes encode MADS box transcription factors.

Question 13

A mutation in the Id protein gene in a vertebrate would most likely affect muscle development by:

Accepted Answer

Reducing the formation of inhibitory heterodimers, allowing more myogenic bHLH proteins to bind DNA and activate muscle-specific genes.

Question 14

Which equation best represents the relationship between gene expression domains and floral organ identity in the ABC model?

Accepted Answer

$$	ext{Petal} = A + B + SEP$$

Question 15

Which of the following best explains why the snake lacks a distinct neck region, according to Hox gene expression patterns?

Accepted Answer

HoxC-6 expression begins at the first vertebra, so all vertebrae develop thoracic identity.

Question 16

Which of the following is a direct consequence of a loss-of-function mutation in a B-class gene (such as apetala3 or pistillata) in Arabidopsis?

Accepted Answer

Petals are replaced by sepals, and stamens are replaced by carpels.

Question 17

Which of the following best describes the process of cell determination?

Accepted Answer

A cell is committed to a particular fate, even if it does not yet show morphological differences.

Question 18

In the context of plant development, what is the primary function of the shoot meristem's organizing center?

Accepted Answer

To maintain the proper number of undifferentiated stem cells by expressing WUS.

Question 19

Which of the following statements about the differences between plant and animal development is correct?

Accepted Answer

Plant development does not involve cell migration, and most plant cells retain totipotency.

Developmental Genetics: Model Organisms, Homeotic Genes, and Pattern Formation

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