Cell Biology Lecture 1.docx

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University of Toronto Scarborough
Biological Sciences
Dan Riggs

Cell Biology Lecture 1 Paraniya Balakumar In the year 2013: many genomes completely sequenced “Bioinformatics” comes of age Most organisms are diploid: two copies of each gene  An allele is an alternative form of the same gene  A genotype is the genetic composition of the organism  A phenotype is the observable traits that an organism exhibits or the morphology Some traits that Gregor Mendol used to establish basis of heredity were to use the genes of tall pea plants VS. short pea plants  He decided to measure his pea plants and disocovered that some of his pea plants were tall and some were short in term of height, tall seems to be dominant trait over short, yellow vs. green, and round vs. wrinkled  The idea here is to understand that for every trait there are at least two forms one of them being dominant to the other one  He followed particular traits by conducting crosses When one conducts a cross a sperm and egg get together; easy in plants as many are self fertile and will do the work by itself Punnett square – gives you a possible of outcome of what you will see when one crosses  Organisms are diploid – let’s look at the contribution of a sperm and the contribution of the egg for one particular gene that being a round vs wrinkled phenotype o If the sperm is carrying either of those two; you use the sperm to fertilize eggs what will happen?  Sperm donates large R and egg donates a large R = progeny is going to round  Only time you will get a wrinkled plant is when you get a small r from the Mendel: Following the round vs wrinkled seed phenotype To understand Mendel’s laws-some vocabulary words: Phenotype: observable traits or morphologyproducing a recessive gene rr o Self crossing of Rr (heterozygous) plant produced a 3:1 ratio of round: Conduct a cross: sperm and eggs get together; easy in plants Homozygous: both alleles are identical (e.g. dominant) wras many are self fertile and will do the work for you.rinkled • If dominant, generally the ‘wildtype’ (RR) Sperm Punnett Square R (round) r (wrinkled) Heterozygous: alleles differ (one dominant, one recessive)= Rr RR Rr R (round) round round Nulls: homozygous recessive (rr) • Generally associated with the ‘mutant’ trait Rr rr r (wrinkled) round wrinkled Self crossing of Rr plant produced 3:1 ratio of round:wrinkled  Homozygous means that both alleles are identical (ex.dominant, recessive). If dominant, generally the “wildtype” (RR)  Heterozygous means that both alleles differ from one another (one dominant, one recessive (Rr)ygote example:Mother donates normal gene; father Example of mutation: Wrinkled peas donates mutant gene: heterozygous progeny often exhibits ‘normal’  Nulls mactivityozygous recessive (rr). It is generally associated with the “mutant” trait. ¼ Recessive allele=wrinkled possibility to get this , and is not found as often Inactive protein or enzyme Known to be due to mutation in a gene encoding a starch branching enzyme 1 Mutation that Transcription, translatioalters genetic code RECESSIVE allele R (round) RR Rr round round Nulls: homozygous recessive (rr) In the case of a heterozygote example in which a mother donates normal gene; and the father • Generally associated with the ‘mutant’ trait donates a mutant gene: heterozygous progeny often exhibits “normal” activity r (wrinkled) wrinkled  Offspring usually exhibit the normal phenotype – presence of the dominant gene  Red shows the father chromosome that has the mutation in the gene (recessive) that mutation somehow alters the genetic code and so that’s not so good Self crossing of Rr plant produced 3:1 ratio of round:wrinkled  Orange shows the mother chromosome that was donated shows the dominant allele and can see that when transcription and translation takes place an active protein or enzyme is produced and so on  Heterozygote example:utMother donates normal gene; fathermay take place but enExample of mutation: Wrinkled peas produced that doesn’t do that right thing but since the mother has donated the dominant donates mutant gene: heterozygous progeny often exhibits ‘normal’ activitysually in these situations of heterozygote you have a normal functioning child Inactive protein or enzyme Mutation that Transcription, translation alters genetic code RECESSIVE allele DOMINANT allele Transcription, translation Seed doesn’t fill properly and thus appears shrunken or wrinkled. Active protein or enzyme As an example there is Mendel’s wrinkled peas; can see in the photograph where there is a peapod with several wrinkled seeds = due to mutation (insertion into the gene of about 800 base pairs of this foreign DNA sequence)  What happens for these wrinkled seeds is that the seed doesn’t fill properly and thus appears shrunken or wrinkled o Starch branching does not occur since there is a insertion of the 800 base pair which in turn disrupts the gene Mendels Laws include the law of segregation and the law of independent assortment  Law of Segregation is when two alleles of a gene segregate from one another into the gametes. Thus, half of the gametes carry one of the alleles and the other half of the gametes carry the second allele o Key is to understand that alleles refer to one gene o Inheritance of the distribution of the alleles of one gene  Law of Independent Assortment is when different genes assort independently during gamete formation. That is, the gene for seed color segregates independently from the gene for seed shape. o Key is to understand that two genes are considered 2 Diploid of course means that there are two copies of each gene and heredity is basically based on two things: a. Sex b. What happens during genesis (different outcome every time) Why do we get a different outcome each time? Sources of variation include: 1. Meiosis which is a reductional division in which haploid sperm and haploid eggs are produced (only donating one or the other two possibility in each sperm or egg) 2. Recombination occurs between maternal and paternal chromosomes to give unique genetic information 3. Specific combinations of a recombinant sperm and egg produces a genetically unique individual  2N cell (diploid) – recombination – 1 division (Homologs disjoin) nd 4N cell  2 x 2N cells – 2 division (Sister chromatids disjoin) 2N cell  2 x 1N cells MITOSIS One diploid "parent" cell divides to produce two genetically identical "daughter" cells. This type of cell division is used for  asexual reproduction in unicellular organisms o Even some multicellular species reproduce via PARTHENOGENESIS ("virgin birth"). o a CLONE is a group of genetically identical organisms produced via asexual means. (It is not an individual organism produced via cloning.) o In times of stress, even species that ordinarily reproduce asexually may revert to sexual reproduction. Why might this be an advantage to the organism?  somatic (body) growth in multice
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