Question 1

Gap genes, segment-polarity genes, and homeotic genes all ________.

Accepted Answer

Gap genes, segment-polarity genes, and homeotic genes are all involved in the regulation of gene expression during Drosophila embryonic development. They all code for transcriptional regulatory factors that control the expression of downstream genes.

Question 2

Suppose you found several Drosophila mutants that possessed additional legs growing out of their head segments. The probable mutation would be found in ________.

Accepted Answer

The development of specific body parts is controlled by homeotic genes. A mutation in these genes can result in a change in the identity of a segment, causing the development of abnormal body parts. In this case, the mutation resulting in the growth of extra legs on the head segments suggests a mutation in the homeotic genes.

Question 3

Which of the following likely has the most Hox genes?

Accepted Answer

Dolphins, being mammals, are more complex organisms compared to jellyfish, slugs, and bees. The complexity and diversity of body plans in mammals typically require a larger number of Hox genes to regulate the development of their structures. Hox genes play a crucial role in determining the body plan and the formation of specialized structures during embryonic development.

Question 4

Which of the following are maternal effect genes that control the orientation of the egg and thus the Drosophila embryo?

Accepted Answer

Egg-polarity genes control the orientation of the egg and thus determine the polarity of the embryo. Maternal effect genes are genes whose expression in the mother directly determines a phenotype in the offspring, and egg-polarity genes are an example of these types of genes. Homeotic genes, segmentation genes, morphogens, and inducers are not maternal effect genes that control the orientation of the egg.

Question 5

During Drosophila development, there is a regulatory cascade of gene activation. The proper sequence for this cascade is ________.

Accepted Answer

The correct sequence for gene activation during Drosophila development starts with the maternal effect gene bicoid, followed by the activation of gap genes, then pair-rule genes, and finally segment-polarity genes. This sequence is crucial for the proper segmentation and development of the embryo.

Question 6

Your brother has just purchased a new plastic model airplane. He places all the parts on the table in approximately the positions in which they will be located when the model is complete. His actions are analogous to which process in development?

Accepted Answer

Pattern formation refers to the process by which cells in a developing embryo acquire different identities according to their relative spatial positions, analogous to arranging model airplane parts on a table in their eventual positions. This process ensures that the parts (or cells) form a coherent structure or pattern, similar to the assembly of a model airplane.

Question 7

Suppose the protein specified by bicoid was injected into Drosophila embryos so that a high concentration was present everywhere in the embryo. What might be the result of such an experiment?

Accepted Answer

Bicoid is a protein that functions as a morphogen in Drosophila (fruit flies), crucial for the early development of embryos. It is normally concentrated at the anterior end of the embryo and establishes the anterior-posterior axis by activating the transcription of genes required for the development of anterior structures. If bicoid were present in high concentrations throughout the embryo, it would interfere with the normal gradient required for specifying the posterior regions, potentially leading to embryos that lack proper development of those posterior regions.

Question 8

The protein of the bicoid gene in Drosophila determines the ________ of the embryo.

Accepted Answer

The protein produced by the bicoid gene in Drosophila determines the anterior-posterior axis of the embryo. This protein is localized at the anterior end of the egg and diffuses throughout the embryo, specifying different cell fates depending on concentration. The posterior-ventral axis is determined by the nanos and caudal genes.

Question 9

The product of the bicoid gene in Drosophila provides essential information about ________.

Accepted Answer

The bicoid gene in Drosophila provides essential information about the anterior-posterior axis, helping to establish the head and tail ends of the developing embryo. The other options are not related to the function of the bicoid gene.

Question 10

The duplication of homeotic (Hox) genes has been significant in the evolution of animals because it ________.

Accepted Answer

The duplication of Hox genes has led to the evolution of unique body plans and structures in different animal groups, allowing for the formation of novel forms.

Question 11

Scientists have found that the lifetimes of mRNAs coding for pair-rule regulatory elements in Drosophila embryos may last only a few minutes. What does this suggest about the overall developmental plan of an animal body?

Accepted Answer

The short lifetime of mRNAs coding for pair-rule regulatory elements suggests that building an animal body requires a sequence of precisely timed steps, with genes being activated and deactivated at specific times to ensure proper development. This highlights the critical importance of timing and sequential gene expression in the overall developmental plan of an animal body.

Question 12

Suppose there was a mutation in the segment-polarity genes of Drosophila. What do you suppose might be the outcome?

Accepted Answer

The segment-polarity genes in Drosophila are involved in the development of the anterior-posterior axis of each segment. A mutation in these genes could result in the incorrect placement of structures within the segment, such as antennae appearing in a different part of their usual segment. Choices A and B are unlikely since the segment-polarity genes are responsible for the patterning of individual segments rather than their formation. Choice C is not directly related to the function of segment-polarity genes.

Question 13

Suppose you have identified a type of lizard that seems to have acquired a mutation in which hindlimbs are absent. Which gene, also responsible for the loss of limbs in snakes, may be mutated in this animal?

Accepted Answer

Sonic hedgehog is responsible for limb development in vertebrates, and its loss of function can result in limblessness or limb reduction. This gene is mutated in snakes, and it is possible that this same gene has been mutated in the identified type of lizard with absent hindlimbs.

Question 14

In combination, the products of gap genes, pair-rule genes, and segmentation-polarity genes ________.

Accepted Answer

The combination of gap genes, pair-rule genes, and segmentation-polarity genes define the segmented body plan of the embryo. Gap genes establish broad regions of the embryo, pair-rule genes divide the embryo into segments, and segmentation-polarity genes determine the identity and polarity of each segment.

Question 15

When the Bicoid protein is expressed in Drosophila, the embryo is still syncytial (divisions between cells are not yet fully developed). This information helps to explain which observation by Nüsslein-Volhard and Wieschaus?

Accepted Answer

The fact that a syncytial embryo still responds to the Bicoid protein suggests that it is diffusing throughout the embryo in a concentration gradient, rather than working through regulated transcription or cell-cell signaling, as these mechanisms would likely require the presence of fully developed cell divisions.

Question 16

Suppose the pair-rule genes were inactivated in Drosophila embryos. What is the likely result of the experiment?

Accepted Answer

Pair-rule genes are responsible for establishing the segmented body plan of Drosophila embryos. Inactivation of these genes typically results in the loss of alternate segments, leading to a pattern where every other segment is missing.

Question 17

Mutations in which of the following genes lead to transformations in the identity of entire body parts?

Accepted Answer

Homeotic genes determine the identity and positioning of body parts during development. Mutations in these genes can lead to transformations in the identity of entire body parts.

Question 18

The bicoid gene product is normally localized to the anterior end of the embryo. If large amounts of the product were injected into the posterior end as well, which of the following would occur?

Accepted Answer

The bicoid gene product is a morphogen that specifies anterior structures in developing embryos, particularly in Drosophila (fruit flies). Injecting it into the posterior end would lead to the formation of anterior structures at both ends of the embryo.

Quiz 21: Genes, Development, and Evolution