Week 1 Flashcards
Genetics
Is the study of genomic sequence variation
Genomes
Are a set of instructions enclosed in a biological compartment
DNA
A chemically inert molecule that stores information
Central Dogma
gene -> transcript -> protein
proteins are associated with chemistry
RNA to some degree as well
Allele
is a sequence variant
How do alleles arise?
No genome is stable. changes occur all the time
replication mistakes;generation of alleles
In a growing population of genomes with no selection pressure,
The total number of alleles increase every generation.
Genomes are not stable
Consequences:
The genome of the zygote accumulates alleles as it divides during development.
The fibroblast cells in your skin will have alleles not present in the zygote.
These new alleles can lead to cancer.
There are no living fossils
Coelacanth first observed in the fossil record 390M years ago. Thought to be extinct for 66 M years. Caught in the 1938. They are lobed-limbed fish and cousins of us as tetrapods. Often called living fossils because of these “primitive features” but remember their genomes like ours has been changing over the past 390M years. They are not primitive.
Genetics is the study of sequence variation. What does it tell us?
It can tell us about history of life and its evolution.
It can tell us about how inheritance works. Mendel and nuclear inheritance.
It can tell us about the chemistry of life. What genes are required for a process, like for instance circadian rhythm.
Protein World
Can catalyze chemical reactions
Can potentially alter other proteins (e.g. prions)
‘Protocells‘ may have existed
concentrated proteins surrounded by lipid membranes.
Generally unstable
Function, but no heredity (can’t store genetic info)
DNA World
Stores genetic information
Very stable
Without other
molecules…. boring
RNA World
Can store genetic info
Can catalyze reactions: Ribozyme
RNA makes proteins
RNA makes more stable template of self in the form of DNA
Three domains of life
Bacteria
Archae
Eukaryotes
they evolved from LUCA
a split occuring between bacteria, eukaryotes and archae followed by a second split between eukaryotes and archae
Why do contemperary animal/protist genomes contain both bacterial and archaea genes?
1/3 of genes are of bacterial origin (alpha proteobacteria)
1/3 are of archaea origin
Last third of eukaryote genes arise from other bacteria or novel genes
Origin of mitochondria is the origin of eukaryota
it has been suggested that archae and alpha-protobacteria got together in a genetic merge to give rise to eukaryote, they are a product of a genetic merger
Steps for creating a eukaryote
- Feeding
- Endosymbiosis
- Sharing
- Entrapment
- Transfer of control and genetic integration
Endosymbiosis
2 distinct organisms
both free-living unicellular & both have a genome
Debate about when organism go from two to one organism:
1-Anaerobic archae
2-alpha proteobacterium aerobic
Scientists believe it’s a continuous process that there is no arbitrary line
feeding
Feeding is not a common phenomenon, branches of archaea have the genetic and protein ability to feed
organism B undigested & inside A B hangs out inside A
Theres a benefit in this relationship, the bacteria provides more metabolites for the host cell
Sharing
The host provides certain metabolites to the endosymbiont and vice versa the sharing is advantageous
but B can still survive outside A
They are still two distinct organisms involved in an endosymbitotic relationship
entrapment
Genomes are not inherently stable, leading to a random mutation, a change in the genome of the host or the endosymbiont such that now the host or the endosymbiont is dependent for life on the other organism
endosymbiotic gene loss
B trapped inside A
an evolutionary ratchet
A genetic change that increases the complexity of a biological system and that is hard to undo.
an evolutionary ratchet
A genetic change that increases the complexity of a biological system and that is hard to undo.
Entrapment
B trapped inside A: the relationship strengthens
Relationship stengths through other random mutations such that the host and endosymbiont are loosing genetic information such that they depend on one another more
Gene transfer
from endosymbiont to host
Genes from the endosymbiont are transferred to the host.
Doing so results in the host gaining better control over the endosymbiont.
How does horizontal gene transfer occur?
The gene is copied to the host chromosome from the endosymbiont, the gene exist in both genomes.
Subsequently the gene in the endosymbiont is lost.
Experimental evidence of gene transfer.
Although this yeast cell has a TRP1 gene, it is in the mitochondrial genome and not expressed, because mitochondria do not have the ability to express nuclear genes.
The TRP1 locus in the nuclear genome is an inactive trp1 allele. Therefore, this yeast can not grow on medium lacking Tryptophan.
Plate the cells on a medium lacking Tryptophan
The TRP1+ locus has been transferred from the mitochondria to the nucleus and is now expressed and the cells can grow on a medium lacking Tryptophan.
why aren’t all genes transfered?
These thirteen genes that produce proteins cannot be produce in the cytoplasm of the host it needs to be produced into in the organelle and then imbedded in the organelle membrane
Consequence of the genetic merger:
Creation of the new domain Eukryota
When we created eukarotes we have an organism made up of two distinct membrane bound comaprtments
Feeding is the use of membranes to swallow food.
The production of energy of mitochondria is the main benefit for genetic merger, the extra energy allows the cell to engage in more complex arrangements of its genome.
All of the processes found in eukaryotic cells are genetically expensive.
Just the beginning of genetic mergeres
origin of chloroplasts
The origin of mitochondria followed by other eukaryotic lineages entering into symbiotic relationship with cyanobacteria
Secondary chloroplast
Non-photosynthetic eukaryote feeds on a eukaryote with a choloroplast
Secondary chloroplast surrounded by an extra member, the choloroplast has been fed on twice
