Flashcards in Topic 3 - chapter 9 Deck (41)
How can we better understand how genes have evolved from first cells?
by comparing nucleotide or amino acids sequences of contemporary organisms
How can genetic variation can be increased? Eg's?
by altering nucleotide sequences of genomes such as:
- gene duplications
- exon shuffling
- horizontal transfer (mainly prokaryotes)
How are point mutations caused? Eg?
Page 301...by failures of the normal mechanisms that copy and maintain DNA
Eg mutant E. coli (can't grow in absence of his) -> stop codon (mRNA) -> add histidine to culture -> bacteria multiply -> mutations -> rare colony of his cells that can grow in absence of his
Examples of point mutation having effect on 'fitness'...
lactase persistence (mutation) -> lactose tolerance
RBC surface receptor mutation -> anti-malarial
What gives rise to families of related genes? How?
DNA duplications via unequal crossing over between homologous chromosomes - statistically rare but are a certainty in billions & billions of cell divisions it took to form all different species from a common ancestor
Give an example of molecular evolution using gene duplication
evolution of the globin gene family including haemoglobin via gene duplication & divergence -> proteins tailored to an organism & its development
Give eg of whole genome duplication
Xenopus frog species (frog twice as big as the one previous)
What are exons also known as?
the 'fixed' building blocks for proteins
T or F - new genes can be created by repeating the same exon
How is the evolution of new proteins thought to have worked?
facilitated by swapping exons (exon shuffling) between genes -> hybrid proteins -> new functions
Some 'prime' examples of new proteins from existing protein domains...?
EGF -> chymotrypsin -> urokinase -> factor IX -> plasminogen
What are mobile genetic elements? what do they frequentyl cause?
parasitic DNA sequences that colonise genome & spread within it -> often disrupt function or alter regulation of genes (can even create novel genes)
frequently cause "spontaneous" mutations
Example of mobile genetic element at work...
Drosophila melanogaster (fruit fly) when inserted in a gene that should be silenced -> activate gene -> legs where antennae should be
What is horizontal gene transfer?
bacteria sex - conjugation - is the transfer of DNA from donor cell to recipient cell via sex pilus
Molecular change is ... while natural selection is ...?
random and progressive
What is the significance between Islands of Conserved DNA Sequence?
They indicate functionally important regions of DNA
Examples of similar gene clusters in mouse & human...
globin clusters (human Alu & L1, mouse B1 & L1)
How much of the human genome is highly conserved compared to other genomes?
T or F - vertebrate DNA gain and lose DNA slowly over time
false - rapidly
What is interesting about the Fugu huntington gene? What does this confirm?
same number of exons as the human version just shorter introns - confirms that exons are more conserved than introns
What does sequence conservation allow us to find out? E.g?
trace the most distant evolutionary relationships - the more important genes are for fundamental cellular processes, the more they are conserved
small subunit of rRNA similar in different organisms
What % of the human genome is exons?
What is the DNA length in the human genome (nucleotide pairs)?
3.2 x 10^9
Number of genes in the human genome? (approx)
The bulk of the human genome is made up of ... sequences?
What gives an idea of positions of genes in a known sequence?
Open reading frames
Individual humans differ from one another how? SNP equivalent?
avg 1 nucleotide pair in every 1000
~ 2.5million SNPs
streches of DNA (added or deleted)
Point mutations change what?
regulation of a gene
Re. genetic variations, define mutation within a gene
gene modification by changing single nucleotides or delete or duplicate one or more nucleotides. Can alter activity or stability of a protein, change its location in a cell or affect its interactions with other proteins