Evolutionary Developmental Biology Lec 14

Question 1

What is evolutionary developmental biology (evo-devo)?

Answer 1

Evo-devo is a field of biology that studies the relationship between development, how traits are produced, and evolution, why we see certain traits. Evo-devo helps explain biological diversity from the perspective of development.

Question 2

All cells have the same genome. How do we get variation?

Answer 2

While all cells have the same genetic instructions, variations arise due to differences in gene expression. How genes are expressed, not just their presence or absence, determines the traits we see.

Question 3

What is morphogenesis?

Answer 3

Morphogenesis is the biological process that causes an organism to develop its shape.

Question 4

How is morphogenesis influenced?

Answer 4

It is influenced by variations in cell properties like how they grow, their shape, how they stick to each other, programmed cell death (apoptosis), and how they respond to hormones.

Question 5

What are transcription factors (TFs) and what is their role?

Answer 5

Transcription factors are proteins that bind to DNA and control the process of transcription, which is the first step in gene expression.

Question 6

What is gene regulation?

Answer 6

Gene regulation is the control of which genes are turned on or off, when, and where. It is fundamental to understanding how evolution uses changes in development to drive new innovations

Question 7

What are epigenetic modifications?

Answer 7

Epigenetic modifications are changes to the structure of DNA that affect gene expression without altering the DNA sequence itself.
Examples include DNA methylation and chromatin modifications.

Question 8

What are regulatory elements and what are the two types?

Answer 8

Regulatory elements are specific DNA sequences that influence gene expression. There are two main types:
■
Cis-regulatory elements: Located on the same chromosome as the gene they regulate.
■
Trans-regulatory elements: Located on a different chromosome from the gene they regulate.

Question 9

What is cell fate determination?

Answer 9

Cell fate determination is the process by which a cell becomes committed to developing into a specific cell type. It’s like a cell choosing its career path.

Question 10

What is cell differentiation?

Answer 10

Cell differentiation is the process by which a cell acquires the specialized features of a particular cell type. This is how a generic cell becomes a specific type like a muscle cell or a nerve cell.

Question 11

What are homeotic mutations?

Answer 11

Homeotic mutations cause one body part to transform into another. These mutations have been really important in figuring out what different genes do.

Question 12

What are Hox genes?

Answer 12

Hox genes are a family of transcription factors crucial for animal development. They are like the architects of the body, telling cells where to go and what to become.

Question 13

What is the function of Hox genes?

Answer 13

Hox genes control the head-to-tail organization of the body and the position of different body parts during development. They are arranged in gene complexes and their expression follows a specific order in space and time.

Question 14

What is the homeobox?

Answer 14

The homeobox is a highly conserved DNA sequence found within Hox genes. It encodes a protein domain that binds to DNA, allowing Hox proteins to act as transcription factors.

Question 15

What is deep homology?

Answer 15

Deep homology refers to the evolutionary conservation of Hox genes and their function across a wide range of animal species. It suggests that diverse organisms use a similar toolkit of genes for development.

Question 16

What influences Hox gene regulation?

Answer 16

Hox gene regulation can be influenced by several factors:
■Maternal morphogen concentrations: The concentration gradients of signaling molecules from the mother can influence which Hox genes are turned on or off.
■Epigenetic factors: Modifications to DNA or its associated proteins, like methylation or acetylation, can also affect Hox gene activity.

Question 17

What is Bicoid?

Answer 17

Bicoid is a maternal morphogen in the fruit fly Drosophila. It establishes the anterior-posterior (head-to-tail) axis of the developing embryo by forming a concentration gradient.

Question 18

What are gap genes?

Answer 18

Gap genes are activated by the Bicoid gradient and define broad regions in the developing embryo. They are the first step in the genetic cascade that leads to segmentation.

Question 19

What are pair-rule genes?

Answer 19

Pair-rule genes are activated by gap genes and contribute to the formation of body segments. They refine the pattern established by the gap genes.

Question 20

What are gene networks?

Answer 20

Gene networks are groups of interacting genes that work together to control developmental processes. They ensure that development happens in a coordinated way.

Question 21

How does evolution “tinker” with genes?

Answer 21

Evolution often works by modifying existing genes and developmental pathways to create new features. It is more like a tinkerer working with available materials than an engineer designing from scratch.

Question 22

What is allometry?

Answer 22

Allometry is the study of how different body parts grow at different rates. This can lead to changes in the shape of an organism as it develops.

Question 23

What is heterotopy?

Answer 23

Heterotopy is when a gene or trait is expressed in a different location in the body compared to its ancestral position. It’s like moving a building block to a new spot in a structure.

Question 24

What is heterochrony?

Answer 24

Heterochrony is an evolutionary change in the timing or rate of development. It can lead to differences in the size, shape, or presence of features in adults compared to their ancestors.

Question 25

What is paedomorphosis?

Answer 25

Paedomorphosis is the retention of juvenile traits in the adult stage. It can occur through neoteny, which is a slowdown in the development of certain body features.

Question 26

How can evolutionary novelties arise?

Answer 26

Evolutionary novelties, or new features, can arise through several mechanisms:
■Co-option of existing pathways: Using existing genes and developmental pathways for new purposes.
■Transcription factor mutations: Changes in transcription factors can alter the expression of many genes.
■Gene duplication events: Having extra copies of genes allows for more opportunities for mutations and new functions to arise.

Question 27

What are the implications of the Ubx gene mutation in insects?

Answer 27

A mutation in the Ubx gene in insects led to the loss of legs in the abdomen. The modified Ubx protein blocks the activity of the Dll gene, which is essential for leg formation. This shows how changes in Hox genes can drastically alter body plans.

Question 28

What is modularity in evo-devo?

Answer 28

Modularity refers to the idea that organisms are made up of semi-independent units, or modules, that can evolve somewhat independently. This allows for more flexibility in evolution, as changes in one module may not affect others.

Question 29

What are phenotypic integration and pleiotropy?

Answer 29

■Phenotypic integration is the interconnectedness of different traits. Changes in one trait can affect others.

■Pleiotropy is when a single gene influences multiple traits. This can constrain adaptive evolution, as a beneficial change in one trait might be linked to a harmful change in another.

Question 30

What are some constraints on adaptive evolution?

Answer 30

Constraints on adaptive evolution are factors that limit the ability of organisms to evolve new traits:

■Lack of genetic variation: If the necessary genetic variants aren’t present, a population can’t evolve in a certain direction.

■Pleiotropy and genetic correlations: As explained above, pleiotropy and genetic correlations can link traits together, making it difficult to change one without affecting others

Question 31

How does Bmp4 expression relate to beak evolution in Darwin’s finches?

Answer 31

Variations in the expression of the Bmp4 gene are associated with differences in beak size and shape in Darwin’s finches. Higher Bmp4 expression leads to deeper beaks. This example shows how changes in gene expression can contribute to adaptive evolution.

Question 32

What is parallel evolution and how does the Pitx1 gene relate to it?

Answer 32

Parallel evolution is when similar traits evolve independently in different lineages.

■Loss of Pitx1 gene expression has repeatedly led to the reduction of pelvic structures in freshwater stickleback populations. This is a classic example of parallel evolution, where the same genetic mechanism is used to achieve a similar adaptation in different environments.

Question 33

Humans and chimps share a high percentage of their genome. Why are they so phenotypically different?

Answer 33

: Even though humans and chimpanzees have very similar DNA sequences, they differ greatly in appearance, behavior, and other traits. These differences highlight the importance of gene regulation. Subtle variations in how genes are expressed can have major effects on an organism’s phenotype.

Question 34

What is phenotypic plasticity?

Answer 34

Phenotypic plasticity is the ability of a single genotype to produce different phenotypes depending on the environment. It’s like an organism having different outfits for different occasions.

Question 35

What is canalization?

Answer 35

Canalization occurs when a genotype produces a consistent phenotype regardless of environmental variation. This means that the trait is buffered against environmental influences.

Question 36

What is genetic assimilation?

Answer 36

Genetic assimilation is the evolutionary process where a trait that was initially plastic, meaning influenced by the environment, becomes genetically fixed, or canalized.