Evolutionary Developement

Question 1

Development and homology

Answer 1

• Similarity between embryos of various animals long noted.
• Similarity in developmental pathway critical to establishing homology.
• German biologist Ernst Haeckel ties this to evolutionary change.

Question 2

Ontogeny recapitulates phylogeny

Answer 2

single celled zygote >>>
jelly-fish like gastrula >>>
worm-like embryo  >>>
fish-like embryo >>>
tadpole-like embryo >>>
tetrapod fetus

Question 3

Ontogeny

Answer 3

Ontogeny (also ontogenesis or morphogenesis) is the origin and the development of an organism: for example, from the fertilized egg to mature form. In time frame, it can cover the study of an organism’s lifespan. The word ontogeny comes from the Greek ontos, “to be”; and from the suffix -geny, which expresses the concept of “mode of production”. In more general terms, ontogeny is defined as the history of structural change in a unity, which can be a cell, an organism, or a society of organisms, without the loss of the degree and type of organization which allow that unity to exist. More recently, the term ontogeny has been used in cell biology to describe the development of various cell types within an organism.

Ontogeny comprises a field of study in disciplines such as developmental biology, developmental psychology, developmental cognitive neuroscience, and developmental psychobiology.

Within biology, ontogeny pertains to the developmental history of an organism within its own lifetime, as distinct from phylogeny, which refers to the evolutionary history of species. In practice, writers on evolution often speak of species as “developing” traits or characteristics. This can be misleading. While developmental (i.e., ontogenetic) processes can influence subsequent evolutionary (e.g., phylogenetic) processes (see evolutionary developmental biology), individual organisms develop (ontogeny), while species evolve (phylogeny).

Question 4

Master genes

Answer 4

Genes that control where, when, and how other genes are expressed.
– Make proteins that signal, activate, mark, or otherwise communicate with other genes and their products.
– Often sequentially expressed in a set pattern.
– Also called “homeotic” (HOX) or developmental regulatory genes.

Question 5

Homeotic genes

Answer 5

Expression of body parts: “Antennapedia” the most famous.

Genes regulate where, when, and how genes will be expressed downstream.
Highly conserved and often
occurring in a multi-gene
families (result of ancestral
duplications?)

Question 6

Master genes also specify similar kinds of structures

Answer 6

• Eye development spurred
by PAX genes
• Even though eyes form
differently, all initiated by
similar genes

Question 7

Variants in the regulatory genes still arise through

random mutation

Answer 7

Selection (natural or otherwise) still acts to shape the effects of the mutation in terms of fitness and frequency within the population.

Question 8

Gene duplication

Answer 8

• Most important source of new genes

• Polyploidy
– More copies of ALL genes

• Misalignment in meiosis cause unequal crossing over.
– One chromosome gets extra copies of a gene

Question 9

Globin genes—an example of a gene family

Answer 9

• 7 á-globin genes on chromosome 16
• 6 â-globin genes on chromosome 11

• Similar in structure:
All have 3 exons separated by 2 introns, repeated sequence motifs that allow us to recognize them as similar.

• Duplications WITHIN á and â globin lineages lead to more copies of each.

• Family includes “pseudogenes” that are non-functional as globin genes.
– Ususally not transcribed
– Pseudogenes may eventually evolve new function or role through changes in sequence or in transcription pattern.