module 1: genes, genome, and the tree of life

learning outcomes

1. Define gene, genome and allele, and differentiate between genes and alleles

2. Analyze genome sequence variation and infer transmission 

3. Identify the major events in the three domain representation of the history of life

4. Identify the steps involved in the genesis of eukaryotic organelles

5. Count the number of genomes at the various stages of endosymbiosis

what is “genetics”?

study of genome sequence variation

what is “genome”?

the complete set of inherited instructions that contribute to the traits of an organism (DNA, RNA, etc)

what is a gene?

• a unit of inheritance

• a piece of instructions that influences the inheritance of traits from one individual to the next

• a specific region / locus of DNA that is transcribed into a single RNA molecule

• the entire DNA sequence that’s needed to transcribe and encode an RNA (including regulatory sequences)

T/F: in recent years, nearly the entire genome is transcribed at low levels, and we’re still in the process of determining what all of the non-coding RNA actually does in the cell

TRUE

T/F: no gene works in isolation

TRUE: all genes are part of a complex regulatory network

what are alleles?

changes to specific DNA sequences / variants

what are examples of replication errors? (2)

1. environmental mutagens

   1. reassortment / recombination

In a growing population of genomes with no selection pressure, the total number of alleles _______ every generation.

increases

how do we estimate origin of alleles?

by comparing alleles, tracing back.

what happens if an allele is advantageous to the organism?

it will always be outcompeted / changing

what are the consequences of constantly-changing genomes?

• the genome of a 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

what are living fossils? what is an example of this?

• living fossils contain “primitive features”

• coelacanth were thought to be extinct when they were observed in the fossil

  • After being caught in the wild, they are actually cousins of us as tetrapods

  • Their genomes have also been changing over the past 390M years

how do we explain that even after constant change in alleles, some traits still remain?

some are more advantageous

what are extant species?

species that are NOT extinct

T/F: coelacanth is our ancestor

NO, we share a common ancestor, just like chimpanzees and humans, we diverged due to the instability of genomes

how do we get speciation?

with enough divergence in alleles

• think of a tree (of life !!)

what is DNA world?

• stores genetic information

• very stable, but chemically inert (not static)

  • without other molecules… no life (biochemical activity)

what is protein world?

• can catalyze chemical reactions

• can alter other proteins (eg. prions)

• ‘protocells’ may have existed - concentrated proteins surrounded by lipid membranes

• generally unstable - lack the ability to pass on genetic information

what is RNA world?

• can store genetic info (in-between level of chemical stability)

• can catalyze reactions: ribozyme = RNA enzyme

• overtime:

  • RNA makes proteins

  • RNA makes a more stable template of self

  • gives rise to the central dogma: DNA → RNA → protein

what is at the centre of the tree of life?

LUCA - last universal common ancestor (~3.5 billion years ago)wha

what are the three domains of the tree of life?

bacteria, eukaryote, archaea

• but they can have cross-overs

what does genetics (study of sequence variation) tell us?

1. about history of life and its evolution

2. how inheritance works

3. the chemistry of life

4. what genes are required for a process or trait