Exam 1: Lecture 6 Flashcards
1
Q
Comparison of Nuclear Gene Content
A
- genomes of diverse organisms can harbor very different numbers of genes
- idea that more complex organisms would have dramatically higher numbers of genes than simple organisms is not true in all circumstances
- Craig Venter and Francis Collins leaders of private and public efforts sequence human genome
2
Q
Gene Duplication (What?)
A
- one path to acquiring new genes
- some cases individual genes are duplicated while in other situations large segments of chromosomes can be duplicated
- often occur as result of error in homologous recombination or from movement of transposable element
- rare cases entire chromosome or genome is duplicated which result from errors in chromosome segregation and cell division
3
Q
Gene Duplication (When?)
A
- can occur during formation of gametes during meiosis as well as mitosis
- several cancers are due to gene duplications in isolated tissues
4
Q
Gene Duplication (Happens? sub-functionalization)
A
- immediately after, both daughter genes are identical in sequence, structure and function
- as time proceeds random mutations knock out complementary functions in two daughter genes thereby leaving each daughter gene to execute subset of tasks that were controlled by ancestral gene
5
Q
Gene Duplication (Happens? neo-functioanlization)
A
- random mutations alter function of only one of two daughter genes.
- results in one daughter carrying out all ancestral functions while other daughter gene acquires new functions
6
Q
Mutatioin That Lead to Neo-functionalization
A
- can affect regulatory models or coding sequences
- note: in hypothetical example in note two daughter genes carrying out same function (coding sequence not altered) but they are doing it indifferent tissues.
- If coding sequence is changed then the actual function of the encoded protein will diverge
7
Q
Gene Gain and Loss
A
-can have profound influence–>lead to evolution of bacterial pathogens and marine phytoplankton from putative brown algae
8
Q
Comparison of Modern Primates
A
- indicates 100’s of genes that have been lost and gained over last 48 million years
- losses and gains could be underlying causes for some of difference that are observed between various primates
- differences between the species can also be cause by differences in DNA sequences of common genes, expression patterns, transcriptional levels and protein modifications
9
Q
Organization of Human Genome
A
- contains approximately 30,000 genes (note each gene found in two copies)
- only 1.5% is taken up by coding portion (exons) of genes
- rest made up of non-coding segments like introns, regulatory and untranslated sequences, intergenic DNA, pseudogenes, gene fragments and satellite sequences.
- last category is made up by remnants of transposable elements
- simpler organisms have higher gene density and thus fewer stretches of non-coding DNA
- also contains mitochondrial genome
10
Q
Mitochondrial Genome
A
-portion of genome is efficiently organized. Contributes 37 genes and almost no non-coding DNA
11
Q
DNA Organization: Sea Urchin
A
- discovered that mRNA transcripts contained only a fraction of the sequences that were found within genomic DNA
- for the first time showed that the nuclear genome contained a significant portion of non-coding sequences
- presaged several discoveries including the identification of exons and introns and the process of RNA splicing
- Sequencing of the Drosophila, mouse, and human genomes confirmed that similar relationships existed in other complex organisms
12
Q
Non-coding DNA
A
- the vast majority of the human genome is comprised of non-coding DNA
- this is true of nearly all eukaryotic organisms
- exception:yeast which is a single celled eukaryote
- yeast genome has high gene density and fewer non-coding DNA segments than other eukaryotes
- Bacterial genomes are even more compact: their genomes are fairly devoid of introns, transposable elements, pseudogenes and repetitive sequences
13
Q
Pseudogenes
A
- inactive genes that are either no longer expressed due to a mutation in regulatory element or is dysfunctional due to a mutation within coding sequences
- can be recognized since they contain sequences that are similar to functional gene
- formation is very common after gene duplication and significant portion of eukaryotic genomes is comprised of inactive pseudogenes
- arise from duplications located relatively close to sister genes while those born from retrotransposition can be located at considerable distances
14
Q
Psudeogene: mutation in regulatory element
A
-duplication event takes place which is then followed by accumulation of deleterious mutations in one of daughter genes
15
Q
Psudeogene: mutation within coding sequence
A
- messenger RNA is converted into cDNA clone by the reverse transcriptase enzyme.
- this DNA copy inserted into genome via retrotransposition.
- original mRNA lacks enhancer and promoter elements, newly integrated cDNA copy cannot be transcribed and is inactive in genome
