Genomes Flashcards
Can crossing over create new mutations?
No because its only reshuffling what’s there not creating anything new
What is the genome?
The genome = the total DNA in any single cell of an organism.
nuclear + mitochondrial (+chloroplast) DNA
When we refer to the genome of an organism we are typically referring to the nuclear genome as opposed to the mitochondrial or chloroplast genome, which would be referred to separately.
What are extranuclear or Organellar DNA and describe?
mitochondrial and chloroplast
mtDNA
ctDNA
Greater similarity to bacterial genomes, reflecting their evolutionary history as free-living organisms.
much smaller
circular, not linear, molecules
inherited independently
generally maternally inherited
non-recombining
What is the size of human mt genome in comparison to nuclear genome?
What is genome measured by?
What is genome size referred to as?
the human mt genome is ~ 16,500bp in length, the nuclear genome is >3 billion bp in length.
The number of nucleotides the DNA of that organism is made up of referred to as base pairs (bp) often measured in Kbs.
The size of the genome is referred to as the C-value and this is the actual individual sequence not the numbers of copies of that sequence.
What does genome not relate to?
What is the C value paradox?
The amount of DNA an organism has (genome size = C-value) does not simply relate to evolutionary relationships or lineages nor does it correlate with the number of chromosomes.
The C value paradox is that the amount of DNA in a haploid genome (the 1C value) does not seem to correspond strongly to the complexity of an organism, and 1C values can be extremely variable.
What can relate to the rate of evolutions?
The rate of increase of the genome correlates positively with the rate of speciation, i.e. lineages which have seen rapid increases in genome size are also the ones that have speciated most rapidly.
What are telomeres?
Long repetitive sequences afford important ‘protection’ from inevitable loss of sequence at the end of chromosomes during replication.They have also been linked to aging process
Cancer cells have found away to divide without their telomere being worn away therefore they can divide infinitely.
What are transposable elements
mobile elements, jumping genes
Sequences of DNA that can incorporate themselves into different parts of the genome.
- may make up ~25-50% of the total DNA in mammalian genomes and a significantly larger portion in plant and insect genomes.
Transposable elements (TEs) can be categorised into two main classes. What are they?
Transposons= the DNA of the mobile element (‘donor DNA’) is excised from its location by an encoded enzyme, transposase, and then re-inserted back into a different region of the genome by the same enzymes. (jumping genes)
Retrotransposons= An RNA intermediate is produced from the donor DNA and then reverse transcribed into cDNA which re-inserts into a different genomic location. This group of mobile DNA is what accumulates and expands the genome. (gene copies itself then copy moves somewhere else) add size to genome which could be reasons of variety in genome sizes.
There are two further sub-classes:
*non-viral
-LINES (6-7 kbp long)
-SINES (300 bp long) ‘hyperparasites’
*viral – encode for a viral shell which allows the retrotransposon to leave the cell and infect other cells/organisms.
What can occur in somatic cells when it comes to transposable elements?
Programmed DNA elimination where large parts of the genome are ‘cut out’ of genome of somatic tissue cells.
However, transposable elements are also known to have had very significant and important roles in the generation of evolutionary novelty.
What can transposons contribute to and give an example?
Transposons can contribute to the creation of new exons and exon shuffling events
A TE insertion causes the polymorphism in melanic forms in the British population of the peppered moth.
