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Lecture 9

Biology 1000a lecture 9.doc

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Biology 1001A
Tom Haffie

Biology 1000a Lecture 9-Origin of Variation Recap; • Circular chromosomes exist in plant chloroplast and mitochondria • Mitosis “checkpoint”= metaphase • Cells in mitosis have 4 x C Notes from Lectures: Genomic Variants • Variants in genomes is what makes people differ from one another • Ventor individual genome sequence showed 1.2 million variants • 25% of variant bases are SNPs (single nucleotide polymorphism); 75% are CNV (Copy Number Variations), inversions, etc. • Each person has about 1000 CNVs affecting 35% of genes • Each person has about 300 variants in insertion of retro elements • According to SNP data, people ofAfrican origin are much more different from each other than any other race. • SNPs arise from replication errors. • This means thatAfrican origins are the oldest, and have the most diversity, which leads to the theory that all humans evolved fromAfrican decent. Mobile elements; the “junk” in the human genome • Mobile elements are different in hundreds of locations in every person • Bacteria elements code for their own mobility (transposase) • Simplest known piece of DNAthat can move on it's own in known as an insertion sequence, or an IS element • Structure of IS element has inverted repeats on both ends, whereas the central sequence codes for a gene known as transposase. • Transposase makes “cuts” in the backbone of a target sequence, which initials the element being able to move. • If two IS elements are nearby, they can move everything between them. • One of the reasons why bacteria are becoming resistant to antibiotics, is because of the genes carried by transposons. • Some elements move with, some without, making a copy • The mobile element is called a “jumping gene” • These mobile elements can move in a replicative way. • IS elements are never free floating; they are always moving around, cutting and pasting from gene to gene • IS elements are considered “biological mutagens”, since they are naturally found in the genome, and cause mutations. They are completely different from chemical mutagens (outside chemical sources which cause mutations in a sequence). • Retrotransposons move via RNA; their mechanisms allows them to be “wandering” along the sequence How retrotransposons move; 1. Retrotransposon possibly including genes is transcribed by RNApolymerase, which produces an RNAcopy. 2. Retrotransposon encoded reverse transcriptase makes DNAcopy. 3. Transpositions occurs, whereas this DNAcopy is embedded in a different part of the genome Retroviruses • Viruses that enter the genome are known as proviruses; i.e. HIV • They have three kinds of genes. • Most retroviruses are imbedded in our genomes, although they cannot get out • These are known as endogenous retroviruses • This increases the “junk” in our genome • One of the most common retro elements in the human genome is Alu-elemennt • Alu element insertion is an OPA1 intron sequence which comes with autosomal disorders. • Mobile elements are attracted by plants • We can determine how long an element has been in our system by the activity of that element, and it's effects. • Replication errors can be repaired • Proofreading by DNApolymerase • Sometimes, mismatches escape proofreading • Motor proteins pull chromosomes across the spindle, rather than the spindle itself pulling the chromosome. • Micro filaments are structures which are responsible
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