Introduction to Evolution II Flashcards
What does the endosymbiosis theory state?
The endosymbiotic theory deals with the origins of mitochondria and chloroplasts, two eukaryotic organelles that have bacteria characteristics. Mitochondria and chloroplasts are believed to have developed from symbiotic bacteria.
What is some evidence for the endosymbiotic evolution of eukaryotic cells?
- mitochondria have their own circular genome which replicates independently of nuclear DNA
- new mitochondria are produced by fission of existing mitochondria
- all mitochondrial genomes share similarity with the Typhus bacterium “Rickettsia prowazekii”
What are plastids?
The plastid is a major double-membrane organelle found in the cells of plants, algae, and some other eukaryotic organisms.
What are plastid genomes?
Plastids possess their own genome, the plastome, and a specific machinery to decode its genetic information.
Plastid genomes encode proteins necessary for plastid function.
What are the four basic processes of multicellularity?
- spatial organisation
- change in form
- growth
- differentiation
Describe the diversity in eye evolution.
The diversity of eyes suggests that they have evolved several times independently (polyphyletic, convergent evolution). However, they also have features in common.
For example, ALL eukaryotes use a homologous family of proteins, opsins, to detect light. Opsins are G-protein coupled receptors that convert light to nerve impulses. Eukaryotic opsins share sequence homology and have diverged to detect different wavelengths of light.
RECAP: What are homolgues, paralogues and orthologues?
- Homologues are related by descent from a common ancestor.
- Paralogues are homologues within the same species.
- Orthologues are homologues between species.
Describe Hox gene evolution.
Vertebrates have four Hox gene clusters, which have arisen from two duplication events of an ancestral chromosome.
What does Pax 6 have to do with the development of the eye?
Being eyeless is orthologous to Pax6 in humans and mice. The ectopic (differently placed) expression of the eyeless gene in drosophilia (fruit flies) leads to ectopic eyes. Pax6 is involved in eye development throughout the animal kingdom.
Does this mean that Pax 6 is a ‘master gene’?
It probably isn’t.
Other genes can induce ectopic eyes. Also, anmals without eyes can still express Pax 6.
Pax 6 is present in, and required for, other tissues. It’s more likely that it organises a gene network required for eye formation.
How can eye loss occur as a result of evolution?
Some animals have evolved from surface-dwelling forms to underground forms
Eye loss is a common feature in such animals (why bother with the energy costs of maintaining eyes that have no use?).
This is exemplified by the Mexican, blind cavefish. Its surface-dwelling ancestor has eyes, but the derived, cave-dwelling form doesn’t.
Morphological differences can be seen in organisms that have a similar genetic background. Expand on that.
Morphological differences are established during development. Even though it’s reproductive, selective pressure acts on the adult form.
Animals share the vast majority of their genes, but the regulation of gene expression differs between them.
How do we know where Homo-sapiens come from?
1) We can get evidence from the fossil record and from molecular analyses.
2) Mitochondria are maternally inherited. The mitochondrial genome replicates independently of the nuclear genome and does not undergo recombination
Similarly, the male Y chromosome does not have a homologous female chromosome to recombine with.
Changes in sequence of mtDNA and the Y chromosome are due to random mutations over time.
Analysis of mtDNA and Y chromosome sequence shows maternal and paternal origin, respectively.
