Question 1

In plants, meristem tissue that becomes committed to develop into flowers is called floral meristem. In Arabidopsis, floral meristem is organized into four concentric whorls of cells, each of which gives rise to a specific organ of the mature flower. The floral meristem is therefore analogous to what cells or tissues in animals?

Accepted Answer

The floral meristem is analogous to any one germ layer of the gastrula in animals, as both are committed to developing into specific structures.

Question 2

What is present in cis-regulatory elements that makes their adjacent genes respond to developmental signals?

Accepted Answer

The answer of What is present in cis-regulatory elements that...

Question 3

A cis-regulatory element may _____ transcription.

Accepted Answer

The answer of A cis-regulatory element may _____ transcription.
...

Question 4

Mutant expression of the Bithorax complex of homeotic genes could lead to a(n):

Accepted Answer

The Bithorax complex is responsible for determining the identity of the posterior thoracic and anterior abdominal segments in the development of the fruit fly. Mutations that result in the expression of these genes in the wrong segments can lead to the development of extra wings.

Question 5

The inference that homeotic genes in vertebrates and their corresponding genes in invertebrates evolved from counterpart genes in a common ancestor is supported by the observation(s) that the genes in vertebrates and invertebrates:

Accepted Answer

Homeotic genes in vertebrates and invertebrates share similarities in DNA sequence and are arranged similarly along the chromosome, suggesting they evolved from a common ancestor.

Question 6

When the Pax6 gene from a mouse is introduced into a Drosophila genome, it induces eye development. The eyes appear to be _____ eyes.

Accepted Answer

The introduction of the Pax6 gene from a mouse into a Drosophila genome induces eye development, but the eyes that develop are still Drosophila eyes. They are not mutant mouse eyes, but rather normal fly eyes with a modified genetic makeup. Therefore, the best choice is C, normal fly.

Question 7

Sox9 and Sox10 are both transcription factors involved in the later stages of the development of the peripheral nervous system. The expression of Sox9 and Sox10 is regulated by the products of another set of genes-Pax3 and Pax7. This interaction between Sox9, Sox10, Pax3, and Pax7 is an example of hierarchical control.

Accepted Answer

The statement correctly describes the hierarchical control between Sox9, Sox10, Pax3, and Pax7 in the development of the peripheral nervous system.

Question 8

The Pax6 gene is a master regulator of eye development, but it does not result in potato eyes. Why not?

Accepted Answer

C) Potato eyes are actually the buds from which new potato plants can grow, and they do not share a common evolutionary origin with animal eyes, which are visual organs. The term "eyes" in potatoes refers to the growth points on the tuber, not to structures for vision.D) The cis-regulatory elements, which are regions of non-coding DNA that regulate the transcription of nearby genes, involved in potato-eye development are indeed different from those regulating eye development in animals. These elements are crucial for gene expression in specific tissues and at specific times, and their differences reflect the distinct developmental pathways and functions between potato eyes and animal eyes.

Question 9

Evolutionarily conserved molecules:

Accepted Answer

Evolutionarily conserved molecules are similar in sequence among distantly related organisms, were likely present in the most recent common ancestor of the organisms possessing them, likely changed little over time because they serve a vital function, and are molecules in which most mutations are likely to be harmful. Therefore, all of these choices are correct.

Question 10

In almost all organisms that have been studied, the genes in Hox clusters:

Accepted Answer

The genes in Hox clusters are arranged in the same order as their function along the anterior-posterior axis of the embryo. This phenomenon is known as colinearity, and it has been observed in almost all organisms. The linear arrangement of the genes in the chromosome corresponds to the order in which they are activated during embryonic development. This colinearity is an important factor in specifying the identity of body segments during development.

Question 11

In mammals, Hox genes:

Accepted Answer

The answer of In mammals, Hox genes:
...

Question 12

When the Pax6 transcription factor is transferred from a donor individual of one species into the genome of a recipient individual of a different species, it:

Accepted Answer

Pax6 is a highly conserved transcription factor across species that plays a crucial role in eye development. When transferred from one species to another, it induces the development of eyes characteristic of the recipient species, not the donor species. This demonstrates the conserved function of Pax6 in eye development across different organisms.

Question 13

Homeotic genes encode very important transcription factors that specify the identity of body parts or segments during development. For example, the development of legs on thoracic segments T1, T2, and T3 and wings on segment T2 is controlled by homeotic genes.

Accepted Answer

Homeotic genes indeed specify the identity of body parts or segments during development. The example of developing legs and wings on specific segments controlled by homeotic genes is also true.

Question 14

Homeotic genes encode transcription factor proteins that bind DNA. The DNA-binding domain of homeotic proteins is called a _____, and is a highly conserved region in many homeotic proteins.

Accepted Answer

The homeotic proteins' DNA-binding domain is called a homeodomain, and it is conserved in many homeotic proteins.

Question 15

Which one of the following statements about homeotic, or Hox, genes is NOT correct?

Accepted Answer

The linear order of Hox genes along the chromosome, the anterior-posterior orientation of the embryo, and timing of expression for the genes in Hox clusters is observed not only in Drosophila, but also in many other animals including mammals.

Question 16

What is the MOST logical explanation of the observation that so many organisms have a Pax6 gene?

Accepted Answer

The presence of a Pax6 gene in many different organisms suggests that all of these organisms share a common ancestor that had this gene.

Question 17

A strain of Drosophila carrying a normal Pax6 gene and also the X-linked gene for white eyes is engineered to express Pax6 in its antennae. What is the phenotype of the resulting flies?

Accepted Answer

The answer of A strain of Drosophila carrying a normal...

Question 18

Which of the following statements is TRUE regarding Drosophila development?

Accepted Answer

All of the choices are correct.

Question 19

Gehring tested the hypothesis that the Pax6 gene acts as a master regulator of eye development by introducing mouse Pax6 genes into the genome of a Drosophila and activating it in the fly's antennae. What happened, and did it support or refute his hypothesis?

Accepted Answer

The experiment resulted in the development of a compound eye on the antenna of the Drosophila, which supports the hypothesis that the Pax6 gene acts as a master regulator of eye development across different species.

Question 20

Master regulatory genes that turn on entire programs of development are often identified because loss-of-function mutations and gain-of-function mutations in the gene have opposite phenotypes. Which type of mutation is recessive? Which type of mutation is dominant?

Accepted Answer

Loss-of-function mutations are recessive because one copy of the gene is sufficient to produce enough regulatory protein to activate the developmental program. Gain-of-function mutations are dominant because even one copy of the mutant gene produces enough regulatory protein to activate the developmental program beyond what is normal or necessary. Therefore, loss-of-function mutations are typically homozygous recessive, whereas gain-of-function mutations are typically heterozygous dominant.

Quiz 20: Genes and Development