Q: Which of the following is a correct sequence of gene activation during Drosophila segmentation, starting from maternal effect genes?

$$\text{Maternal effect genes} \rightarrow \text{Gap genes} \rightarrow \text{Pair-rule genes} \rightarrow \text{Segment-polarity genes}$$

Question 1

Which of the following best describes the role of morphogens during animal development?

Accepted Answer

Morphogens are molecules that act in a concentration-dependent manner to convey positional information and influence cell fate.

Question 2

A Drosophila larva develops with two posterior ends and no head structures. Which gene is most likely mutated in the mother, and what does this demonstrate?

Accepted Answer

The bicoid gene is mutated; this demonstrates a maternal effect where the mother's genotype determines the offspring's phenotype.

Question 3

Which experimental result would indicate that a transplanted embryonic tissue is 'determined' rather than 'undetermined'?

Accepted Answer

The transplanted tissue develops according to its original fate, regardless of its new location.

Question 4

Which of the following is a correct sequence of gene activation during Drosophila segmentation, starting from maternal effect genes?

Accepted Answer

$$	ext{Maternal effect genes} ightarrow 	ext{Gap genes} ightarrow 	ext{Pair-rule genes} ightarrow 	ext{Segment-polarity genes}$$

Question 5

A mutation in the even-skipped gene of Drosophila results in the loss of every other segment. Which class of segmentation gene does even-skipped belong to, and what is the phenotype called?

Accepted Answer

Pair-rule gene; pair-rule phenotype

Question 6

Which of the following statements about the Notch signaling pathway is TRUE?

Accepted Answer

Notch signaling involves a receptor that is cleaved, releasing an intracellular domain that enters the nucleus to regulate gene expression.

Question 7

A Drosophila mutant exhibits four wings instead of two. This phenotype is most likely caused by a mutation in which gene complex, and what type of gene is affected?

Accepted Answer

Bithorax complex; homeotic gene

Question 8

Which of the following best explains how the asymmetric distribution of cytoplasmic determinants can result in two different daughter cells after cell division?

Accepted Answer

During asymmetric cell division, cytoplasmic determinants are unequally partitioned, so only one daughter cell inherits them, leading to different cell fates.

Question 9

Which of the following is a function of cell adhesion molecules (CAMs) during development?

Accepted Answer

CAMs help convey positional information by mediating cell-to-cell and cell-to-extracellular matrix adhesion.

Question 10

A gain-of-function mutation in the Antennapedia gene causes Drosophila to develop legs in place of antennae. What does this reveal about homeotic gene function?

Accepted Answer

Homeotic genes specify segment identity, and misexpression can transform one body part into another.

Question 11

Which of the following best describes the molecular structure and function of homeotic proteins?

Accepted Answer

They contain a homeodomain, which is a DNA-binding domain encoded by a 180 bp homeobox, and a transcriptional activation domain.

Question 12

Which of the following is a direct consequence of a loss-of-function mutation in a gap gene such as Kruppel in Drosophila?

Accepted Answer

A contiguous group of segments is missing from the larva.

Question 13

Which of the following statements about maternal-effect genes is correct?

Accepted Answer

Maternal-effect genes are expressed in the mother and their products are deposited in the oocyte, determining the axes of the embryo.

Question 14

Which of the following best explains the phenomenon of lateral inhibition during development?

Accepted Answer

A cell adopts a particular fate and inhibits its neighbors from adopting the same fate, resulting in a scattered pattern of differentiated cells.

Question 15

Which of the following is NOT a variable that can affect the outcome of Notch signaling?

Accepted Answer

The presence of cytoplasmic determinants in the oocyte

Question 16

Which of the following best describes the relationship between the order of homeotic genes on the Drosophila chromosome and their expression domains?

Accepted Answer

The order of homeotic genes on the chromosome corresponds to the anterior-to-posterior order of their expression domains in the embryo.

Question 17

Which of the following is a real-world example of a master switch gene, and what is its significance?

Accepted Answer

The eyeless gene in Drosophila, which can induce the formation of eyes in non-eye tissues when misexpressed.

Question 18

Which of the following best explains why a female Drosophila homozygous for a bicoid mutation produces 100% abnormal offspring, even when mated to a wild-type male?

Accepted Answer

The bicoid gene product is provided to the oocyte by the mother, so the zygote cannot compensate with its own genotype.

Question 19

Which of the following is a correct description of the function of Polycomb and Trithorax group genes in homeotic gene regulation?

Accepted Answer

Polycomb genes repress homeotic gene expression by promoting closed chromatin, while Trithorax genes activate homeotic gene expression by promoting open chromatin.

Developmental Genetics: Principles and Mechanisms (Drosophila Focus)

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