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Karen Ing (37)
Lecture 12

Env200 march 5 lecture 12.docx

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School of Environment
Karen Ing

Env200 march 5  Two cell division processes o Mitosis (cell cloning)  Cell division that produces two identical daughter cells (the kind of cell division associated with growth and cell replacement) o Meiosis (gamete or egg and sperm production)  Cell division that produces daughter cells with half the original number of chromosomes (the kind of cell division associated with reproduction ro production of new individuals)  Sexual reproduction o Humans have 23 pairs of chromosomes in each cell of our bodies (except in our egg and sperm cells) o Meiosis- a type of cell division that cuts chromosome numbers in half (in contrast to mitosis which simply duplicates cells) o If there were no process to cut the # of chromosomes in half, fertilization of eggs by sperm would lead to a doubling of chromosome number o So meiosis creates eggs and sperm cells with only 23 chromosomes (rather than 23 pairs) o Fertilization restores the correct number of chromosomes to 46 (23 pairs) o Each pair of chromosomes splits independently  Human Karyotype o 1a and 1b, 2a and 2b, 3a and 3b etc o How many diff versions of gamete could we make with 23 pairs of chromosomes if each pair splits independently?  Ex: 3 chromosomes  1 a and 1b, 2a and 2b and 3a and 3b  Each gamete is going to end up with one allele of chromosome 1(a or b) one allele of chromosome 2 (a or b) and 3(a or b)  If there were 23 pairs of chromosomes  223= 8, 388, 608 (independent assortment alone is capable of generating over 8 million different gametes) o A gamete (egg or sperm) is not a new individual, we need 2 gametes to restore the correct chromosome #  Each of the 8 million and gametes has an equal chance of being fertilized by one of 8 mill and other gametes  8, 388, 608 x 8,388, 608 = 70, 368,744,177,644 (each of us is a 1 in 70 trillion event)-so to find a clone of yourself you have a 1 in 70 trillion chance  Sex chromosomes o 23 pair of human chromosomes o Xx female; xy male o Sex linked traits on x chromosomes (1000 ish genes)  Ex: colour blindness, hemophilia, male patterned baldness  Y chromosome (26 genes, but very important) this is where you’d get certain maley traits  Review of evolution o Evolution is survival of the fittest  Fitness defined as number of offspring that survives to the next generation o Adaptations that improve fitness are selected for o Adaptation possible because of genetic diversity o Mutation is one source of genetic diversity o Mechanism capable of changing gene frequency (evolution)  Natural selection  Sexual selection-non random mate choice  In the natural world animsl don’t randomly mate with others some do, however it is a deliberateness  Genetic drift founder effect  Do mistakes happen? o Yes but not very often on genomic DNA o Data suggests: Dna substitutions occur about once every billion DNA nucleotides (made once a month per cell); very rare  Dna repair proteins “patrol” dna repairing mistakes (usually substitution of an incorrect nucleotide)  However this apparent consistency to rates of change in dna turns out to be useful as a molecular clock o Genetic diversity: some mistakes (really just changes) do not get repaired and we have a new version of the gene, one with a different sequence of nucleotides. o Different forms of the same gene called alleles.  Ex: in the fruit fly, there is one allele of the eye colour gene that codes for white and another for red. In humans there is an allele for blue eyes and a diff one for brown- but we all have a gene for eye colour  Sickle-cell anemia, a serious hereditary red blood cells disorder is the result of a single point mutation o However just as mutations can be lethal, it is also possible that a new protein created by a mutation could be advantageous  We can use the case of the peppered moth presence to understan
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