Genomics and Evolution Flashcards
(193 cards)
Chromosome number changes via which two mechanisms?
Fusion (reduction)- Muntjacs, for example have just 4 chromosomes due to fusion,
Fission (increase).
Chromosome structure changes via which mechanisms?
Inversions,
Translocations,
Segmental duplications.
What is a ‘pseudoautosomal region’?
Small region of homology between sex chromosomes. Humans have two, one at each end of chromosomes.
Platypus has 5 pairs of X and Y chromosomes, how does such an arrangement emerge?
Translocation of regions between sex chromosome and autosomes, this creates a small region of the sex chromosome which is homologous to an autosome and vice versa. During meiosis, these regions chain together, causing chromosomes to segregate as a group.
How do sex chromosomes typically evolve?
From a pair of autosomes that acquire a sex determining gene. Recombination is suppressed in the region surrounding the gene in the heterogametic sex. The non-recombining region can expand by inversions, resulting in nearly entire Y(or W)-chromosome becoming non- recombining
What is the impact of non-recombination on the Y chromosome?
Rapid (almost instantaneous in an evolutionary sense) degeneration and gene loss, with only a few indispensable genes remaining functional.
What do the loss of the ability to synthesise vitamin C in primates and the loss of teeth in birds have in common.
Both represent the general tendency for genes which become unnecessary to be lost.
Unnecessary genes become lost or defunctionalised all the time, but where do new genes come from?
Exon shuffling- exons are recombined into genome at new positions,
Gene duplication,
Retroposition- genes are reverse transcribed into new positions,
gene fusion/fission,
De novo origination.
What is alternative splicing?
When the same pre-mRNA is spliced in an alternative way to produce a new protein.
How did alternative splicing emerge?
Alternative splicing is thought to be a by-product of splicing noise – imperfect or incorrect splicing that occasionally occurs.
What are the two main theories of intron evolution?
Introns early- evolution of introns in RNA-world, and gradually lost in prokaryotes.
Introns late- introns evolved in the ancestor of eukaryotes.
What is the 2R hypothesis?
Vertebrates originated following two rounds of whole genome duplication
How does colour vision in primates illustrate evolution by gene duplication and sub-functionalisation?
Evolution of trichromatic colour vision in primates occurred as a result of gene duplication: the L- gene (for Long wave length) was duplicated and the resulting genes diverged little bit, resulting in L- and M-genes (for Medium wave length).
What is the C-value paradox?
Why do larger genomes not correlate with higher complexity in eukaryotes, as they do in viruses and prokaryotes?
How is the C-value paradox resolved?
The high abundance of non-coding DNA in eukaryotic genomes.
How can genome size be determined for extinct animals such as dinosaurs?
The size of pores inside the bones – the larger the genome, the larger the cell and therefore the larger the pore.
How does rate of DNA loss impact genome size?
The frequency and size of deletions occurring in the genome determines how efficient is genome downsizing. For example: * This study demonstrated that half-life of a piece of junk DNA (e.g. a pseudogene [broken gene]) in Drosophila is only 14 million years, while in the cricket it is over half a billion years – effectively junk DNA is never removed from Laupala genome. This results in hugely different genome sizes
Why is mtDNA useful for phylogenetic reconstructions in humans
mtDA mutates more frequently than nuclear DNA and it does not have recombination.
When was the mitochondrial “Eve” likely to have lived?
Molecular clock suggests mitochondrial Eve lived somewhere in Africa ~170,000 years ago.
When are humans likely to have first migrated out of Africa
75kya
How can we distinguish between migration and selective sweeps when using mtDNA to understand human origins?
It is impossible using only mtDNA. So it is important to look at other parts of the genome unlinked to mtDNA to reconstruct an unbiased picture of human pre-history.
Why is it challenging to use nuclear autosomal genes when reconstructing the history of human populations?
They recombine, which makes them poorly suited for phylogeny reconstructions. Instead, Principle Component analysis (PCA) is used for the analysis of polymorphism in autosomal DNA sequences.
Why does analysis of autosomal genes provide a more robust history of human populations?
Recombination leads to independence of evolutionary histories of different genes, as such, analysis of recombining nuclear autosomal genes provides a more complete picture compared to non-recombining markers.
How are traditional land inheritance practices reflected in human evolutionary genetics?
Comparison of mtDNA (mother-to-daughter) and Y-linked markers (father-to-son) reveals a lot more isolation by distance for the Y-linked markers, indicating much lower mobility of men compared to women, reflecting daughters moving to marry into different families.