where do new genes come from?
A) Gene duplication via 2 mechanisms:
1) Unequal crossing over:
-usually homologous chromosomes line up equally during meiosis, but if there is a place where there are many repeats, they may line up misaligned.
-the inner chromatids (the two strands that are from diff chromosomes that are next to eacchother (think XX, where the X is touching) they cross over.
-now one of the new genes has a duplication, and one has a deletion (cuz it was misaligned)
-new genes formed
2)Duplication via retroposition:
-parent gene is transcribed into nascent (raw) mrna , it contains both intros and extrons
-introns get spliced out of mrna
-reverse transcriptase enzyme copies the processes rna back into DNA (but the introns are not there so they ar enot copied)
-this dna copy is inserted back into genome at new location therefore NEW GENE bc doesnt have introns
-new gene may be pseudofxnal because doesnt have the regulatory sequences to transcribe it to mrna
BUT by chance may insert next to another gene with regulatory sequence so that it can be transcribed and used (funxtional)
-“may represent new copu of a existing gene”
b)Derived from scratch
-basiclaly a previously non-coding region of dna gets a random mutation that creates a start signal (promoter) that cuases the cell to produced nascent mrna , and if the gene can produce a protein that isnt toxic and is needed, natural selection keeps it.
-or a previous stop codon is mutated to no longer be a stop codon so what is transcribed is longer
(ie for chimps, gorilla, etc, there is a point in dna that is a stop codon but for humans it is not )TGA-> CGA
What is the difference between the gene duplication methods listed above?
Gene duplication via unequal crossing over have the same introns and occur in tandem on same chromosome
-genes formed via retroposition do not have introns and may be far from original gene
Chromosomal mutations
-may affect gene ORDER and organization AND/OR produce duplications or deletions that affect a large amount of genetic information
1) inversions:
-a segment of dna from a chromosome breaks off , flips 180 and rejoins at the same chromosome but fliped
ex: Drosophilia subobscura (in both south and north amera, the frequency of inversiono increases as u move further from equator, theis means that the inversion is a trait that helps the flies fly in high altitue, cold climates “parallel evolution” , the genes in that inversion help the flies in the same wau.
2) genome duplication:
-the entire genome is duplicated (polyploidy, specifically autopolyploidy)
-happens when a mutation causes something (like a plant) to produce diploid gametes INTSTEAD OF HAPLOID
-then when the plant self fertilizes, the “kids” are 4n (tetraploid) so this new plant becomes reproductively isolated from the parent and is a “new species” made ina. single generation
2N -> 4N (slide28)
