Week 8: Evolution and Development

Question 1

What are homeotic transformations as per Bateson?

Answer 1

documented abnormalities in invertebrates and vertebrates. He called homeotic transformations - common in regions that were repeated/segmented. Hypothesized that these changes would lead to an understanding of the evolution of animal body plans.

Question 2

What are homeotic genes?

Answer 2

genes that determine the identity and position of anatomical features during development.

Question 3

What are segmentation genes?

Answer 3

• influence patterns of body segments during development.

Question 4

What did the discovery of homeotic genes lead to?

Answer 4

field of Evo-devo - fusion of evolutionary and developmental biology

Question 5

What is Haeckel’s theory of recapitulation?

Answer 5

ontogeny recapitulates phylogeny - developmental processes of an organism replays the evolutionary history of the organisms - rejected because NS acts at all stages of development - embryonic develop is not a replay of phylogenetic history but a mix of it and adaptation.

Question 6

What is Von Baer’s law?

Answer 6

embryos in closely related species resemble each other - similar characteristics appear early in development. Specialized traits appear later and distinguish between species.

Question 7

Describe the genes that control embryonic development

Answer 7

Few genes control embryonic development - similar across species.

Question 8

What is heterochrony?

Answer 8

Timing of development of physical traits relative to development of traits in ancestral species. May be little difference in DNA sequences but difference in timing of expression of genes.

Question 9

What are the 4 types of heterochrony?

Answer 9

Acceleration, progenesis, neoteny and hypermorphosis

Question 10

Describe acceleration

Answer 10

descendant somatic trait occurs earlies but descendent reproductive trait occurs at same time

Question 11

Describe progenesis

Answer 11

descendent somatic trait occurs at same type but reproductive trait is early.

Question 12

Describe neoteny

Answer 12

descendant somatic trait is later and reproductive trait is the same. ie. in axolotl. Retention of juvenile features in adult.. In tiger salamanders there is a TH spike that causes it to lose gills and develop tail suited to terrestrial life. The TH spike does not occur in axolotl, but if raised in an environment with the spike, it develops into a terrestrial form.

Question 13

Describe hypermorphosis

Answer 13

descendant somatic trait occurs at same time but reproductive trait occurs later.

Question 14

What type of cells are early embryonic cells and what is their development guided by?

Answer 14

Early embryonic cells are totipotent - could develop into any cell type. Development is guided by genetic switches that impact protein production, growth of cells and general body plan of plants and animals. Largely depending on timing of genetic switches.

Question 15

What are homeotic genes?

Answer 15

proteins from combinations of these genes act as gene activation signatures to create instructional map to determine where structures should develop. They have critical role in development of phenotype. NS acts on phenotype.

Question 16

What are Hox genes

Answer 16

determine anterior-to-posterior positioning of structures. A subset of homeotic genes code for transcription factors that impact the anterior-to-posterior positioning of structures by regulating gene expression. ie. Abdominal B gene is expressed in abdominal body parts near end of fruit fly.

Question 17

Describe Hox genes in different species ie. in plants

Answer 17

Hox genes also present in other species ie lateral line in fish p allows it to interpret surroundings.

MADS-box genes - homeotic genes in plants.

Question 18

What is a homeobox?

Answer 18

same 180bp sequence found in all homeotic genes in various animals - allowed discovery of more Hox genes as it is the starting sequence for Hox genes.

Question 19

What is colinearity?

Answer 19

position of the Hox gene parallels that of the position of the body part which the hox gene regulates.

Question 20

What evidence indicates Hox genes are homologous?

Answer 20

Homeobox and similar ordering of chromosomes in vertebrates and invertebrates

Question 21

What happens when swap Hox genes?

Answer 21

inserted mouse Hox-2.2 gene into head region of fruit fly genome - produced legs instead of antennae on their head. Homeotic genes have deep ancient ancestral homology.

Question 22

Why is there a deep homology in homeotic genes?

Answer 22

early developmental stages are highly resistant to change, mutations in the genes are likely lethal, homeotic genes are fundamental to early developmental stages that determine overall body plan required for proper functioning of systems.

Question 23

What are gene switches?

Answer 23

transcription factors operate by binding to regulatory enhancer regions of DNA - act as switches to turn genes on/off and are responsible for differential expression of genes. It is one of the reasons why chimps and humans share 98.7% of the genomes but look and act very differently.

Question 24

What is gene duplication, pseudogene and paralog?

Answer 24

Gene duplication - establishment of multiple copies of genes within genome - influential for new evolutionary lineages - may be lost due to selection or become a pseudogene (functionless) or may become a paralog (continue to be expressed) and can evolve separately.

Question 25

Why are duplicated genes maintained? What is subfunctionalization and neofunctionalization? Give example of opsin

Answer 25

Duplicated genes are maintained because they may influence gene expression by increasing the production of histones, ribosomal RNA and other products.

Subfunctionalization- division of labour by paralogs. Neofunctionalization - divergence of paralog and adoption of new, related function.

Examples: humans have 3 copies of opsin allowing us to see reds and greens - dogs have 2. Humans have 400 genes for smell receptors that evolved from a single gene and dogs have 800, cows have 1000.

Question 26

Describe Neural crest cells

Answer 26

embryonic stem cells that become different types of cells - development controlled by developmental regulatory genes ie. Hox, snail, Dlx. Initially near the neural tube then migrate to new locations giving rise to different tissues.

Question 27

What did Scneider and Helms propose?

Answer 27

beak proportions are determined early in ontogeny by development of neural crest cells. Transplanted neural crest cells from duck to quail embryo and vice versa and generated a duck with a short beak and a quail with a longer beak.

Question 28

What did neural crest cells evolve from?

Answer 28

similar ancestral cells - similar cells near notochord in early chordates. They possibly evolved via gene duplication.

Question 29

Summarize

Answer 29

homeotic genes and regulatory enhancers control a lot of the developmental process

Small changes in timing of spatial positions during ontogeny can lead to large-scale phenotypic changes which are under NS.

NS on phenotypes can lead to speciation.