Developmental Patterning Genes - Online Tutor, Practice Problems & Exam Prep

Developmental patterning genes are crucial in determining the organism's body plan, with anterior (front), posterior (back), dorsal (top), and ventral (bottom) orientations. Maternal effect genes, like bicoid and nanos, establish initial gradients that activate zygotic gap genes, which further segment the embryo. This cascade continues with pair-rule and segment polarity genes, ultimately leading to the expression of Hox genes that dictate organ development. In plants, similar homeotic genes (Class A, B, C) control floral structures, demonstrating the conserved nature of developmental genetics across species.

Segmentation Genes

Hi. In this video, we're going to be talking about developmental patterning genes. So, the very first stage of development is really just determining which part of the organism is going to become the front, the back, the top, and the bottom. And so let's learn the names, like the official scientific names of front, back, top, and bottom. So, there's anterior, this is going to be the front, also you can think of it as a head. You have posterior, which is the back. You have dorsal, which is the top, and ventral is the bottom, and I have a picture of this. And then there are going to be many different genes that control the positioning, also called the patterning, of these locations. So there are 2 classes, we have the maternal effect genes, and these are actually maternal genes, so they come from the egg themselves, so from the mother, not the organism that's developing. And so these are found within the egg, and these are the very first developmental genes that happen. So before the organism starts doing anything with its own genes, the mom's genes actually impact development. It's the earliest portion of development. Then after those maternal genes are activated, they're doing their work, they generally activate the second set, and these are the zygotic genes. So this is that organism that's developing. We have the anterior, posterior, dorsal, and ventral. Anything in a circle you need to know, the rest of it you can just scribble out. And so those are the different locations of the fish, and most organisms.

So now let's talk about the genes. So we have segmentation genes that are the first genes that come into play, and these control specific segments of the organism. That's going to be what's going to be the head in an insect, that's what's going to be the antenna, what's going to be the thorax or the abdomen, these types of segments even before they become thorax antenna that actually happens later. But it's just sort of segmenting it saying, okay, this is going to be the anterior end, this is going to be posterior, dorsal, ventral side, and there's going to be some segments in there, so even before we get to specific things like the abdomen. So like I said before, the very first genes that come into play are the maternal effect genes, and so the 2 that are really important are going to be bicoid and nanos. So we have a cell. Right? This is our cell, this is the cell we start off with, and what forms the anterior and posterior end is actually concentrations of these two genes. So we'll say that bicoid is going to be red, and the higher concentration that there is, so over here with a lot of it over here, is going to be the anterior region. Whereas, nanos is going to be opposite. The higher concentration that it has, so over here, is going to end up being the posterior side of the organism. So this is the very first name that controls the position of the organism, it happens in the single cell, and it happens through maternal genes. These are the mom's genes, not the zygote genes. Once we have bicoid and nanos expressed, these genes go on to express the second set of genes, which are gap genes, and these are zygotic genes. These are the first genes of the actual organism that's developing, and this divides the embryo into body segments, and I've mentioned just a couple of ones that you might read about in your textbook, these are the gap genes. The gap genes then go on to ac...

Plant HOX genes

Okay. So now let's talk about plant development and plant genes. So far we've all talked about animals, but plants actually contain their own set of homeotic genes or Hox genes. And so, in Arabidopsis, which is typically the model organism used to study plants. There are 3 classes of Hox genes, very easily labeled Class A, B, and C. Now, in the plant, class A forms the sepals. If you have a segment that's expressing A and B, that's going to be the petals. You have a set of region expressing B and C, that's going to be the stamen. And if you have a thing that's expressing only C, that's going to be the carpels.

If you're like me and aren't really quite up to date on your plant anatomy, let's refresh this. So here's the plant, obviously you know the petals. Right? There's lots of things here, you don't need to know this, we're not in a plants class. Right? But we, the things that we are interested in, we're interested in sepals, petals, stamens, and carpels. So here's the stamen, so this thing here is the stamen. Right? We have petals, which we did here. We have the carpels, which is actually going to be, this green thing here is the carpel, and the sepal is actually these little baby leaves down here, the sepal. So these are the 4 things we're worried about. So if we look over here at this plant, you can see the classes are down here. So Class A is blue, B is yellow, and C is red. Class A forms the sepal, which you remember are these little baby leaves down here. So if we look at where only A is expressed, that's the sepals. If we look at where A and B are expressed, so anything with blue and yellow on it, that's going to be the petals, which are things we're most familiar with. If we look at B and C, so yellow and red, that's going to be the stamen. Remember the stamen is this thing here, so that's there. And then finally, Class C forms the carpal, which is only red, and that is here, carpal stamen, petal, and sepals. Just in case you're not familiar with plant development, hopefully that helps, but this is plant development. They use these Hox genes as well, they're just labeled class A, B, and C, instead of the ones that are labeled, you know, that way in fruit flies. So, with that, let's now move on.

Which genes are the first genes that control patterning of the offspring during early development?

• A. Anterior genes
• B. Maternal effect genes
• C. Zygotic genes
• D. Dorsal genes

Areas with higher bicoid expression will develop into which body pattern?

• A. Anterior
• B. Posterior
• C. Dorsal
• D. Ventral

Activation of the segmentation genes occurs in which of the following orders?

• A. Maternal effect → gap → segment polarity → pair rule
• B. Gap → maternal effect → pair rule → segment polarity
• C. Maternal effect → gap → pair rule → segment polarity
• D. Segment polarity → pair rule → gap → maternal effect

Which of the following HOX clusters are responsible for forming the abdominal in Drosophila development?

• A. Segment polarity
• B. Antennapedia
• C. Bithorax
• D. Pair rule

In Arabidopsis, which class of HOX genes are responsible for forming the plant carpels?

• A. Class A
• B. Class B
• C. Class C
• D. Class B and C

Here’s what students ask on this topic:

What are the roles of maternal effect genes in developmental patterning?

Maternal effect genes are crucial in the earliest stages of development. These genes, such as bicoid and nanos, are derived from the mother and are present in the egg before fertilization. They establish initial concentration gradients that determine the anterior (front) and posterior (back) ends of the developing embryo. Bicoid is concentrated at the anterior end, while nanos is concentrated at the posterior end. These gradients activate the zygotic genes, starting with gap genes, which further segment the embryo. Thus, maternal effect genes set the foundational body plan of the organism.

How do Hox genes influence organ development in animals?

Hox genes, also known as homeotic genes, play a pivotal role in determining the identity and positioning of body segments and organs during development. These genes contain a specific DNA sequence called a homeobox, which encodes a protein domain that binds to DNA and regulates the expression of other genes. In fruit flies, for example, Hox genes are organized into two clusters: antennapedia and bithorax, which control the development of the head, thorax, and abdomen. By activating or repressing target genes, Hox genes ensure that each body segment develops the appropriate structures, such as legs, antennae, or wings.

What is the significance of concentration gradients in developmental patterning?

Concentration gradients are essential in developmental patterning as they provide spatial information that guides the formation of body axes and segments. For instance, maternal effect genes like bicoid and nanos create gradients in the early embryo, with high concentrations at specific ends. These gradients activate subsequent sets of genes, such as gap genes, pair-rule genes, and segment polarity genes, in a sequential manner. Each gene set is activated at specific concentration thresholds, ensuring precise spatial and temporal control over the development of body segments and structures. Disruptions in these gradients can lead to severe developmental abnormalities.

How do gap genes contribute to embryonic segmentation?

Gap genes are the first set of zygotic genes activated by maternal effect genes like bicoid and nanos. They play a critical role in dividing the embryo into broad regions or segments. Gap genes encode transcription factors that regulate the expression of pair-rule genes, which further refine the segmentation pattern. Examples of gap genes include hunchback, Kruppel, and knirps. These genes are expressed in specific regions of the embryo, and their expression patterns help establish the anterior-posterior axis and the initial segmentation of the developing organism. Mutations in gap genes can result in the loss of entire segments.

What are the differences between animal and plant homeotic genes?

While both animals and plants use homeotic genes to control development, there are key differences. In animals, Hox genes are responsible for segment identity and organ development, such as the formation of legs, antennae, and wings in fruit flies. These genes are organized into clusters and contain a homeobox sequence. In plants, homeotic genes are categorized into classes A, B, and C, which control the development of floral structures like sepals, petals, stamens, and carpels. Despite these differences, both animal and plant homeotic genes function as transcription factors that regulate the expression of other genes to ensure proper development.