Genetics week one notes
Genetics week one notes Biology 215
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This 5 page Class Notes was uploaded by Kayla Notetaker on Sunday April 10, 2016. The Class Notes belongs to Biology 215 at Northwestern University taught by Professor peterson in Spring 2016. Since its upload, it has received 13 views. For similar materials see Genetics in Biology at Northwestern University.
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Date Created: 04/10/16
Genetics Day 1 Organisms have programs to respond to their environment and reproduce Genetics is the study of information underlying programs and how these are transmitted Molecular biology includes the study of the molecular processes underlying gene structure and function Class broken down into three units Unit 1: Classical Genetics-Inherited traits, mendel, etc Unit 2: Molecular Biology-Expressed traits Unit 3: Genes in action-Development, human disease, etc Two methods for genetics Method 1: Identify parts and see what they do by themselves (biochemistry approach) Method 2: Identify variants defective for specific processes (genetics approach) Two main branches of life Prokaryotes (bacteria) and Eukaryotes (animals and plants) In biology there are six levels of organization HumancellsNucleusChromosomesGenes in DNADouble helix Genes are encoded on regions of DNA DNA is tightly coiled and condensed around nucleosomes This is the source of information for genes and cells DNA is like the instructions in a cell and Proteins perform the actions of a cell Genes encoded into DNA and translated into proteins Approximately 20,000 genes in the human genome (not that many) What are proteins? Linear polymers of amino acids This is a string that is created through a dehydration reaction (releasing H2O) There are 20 different kinds of amino acids and each have different properties Proteins fold into 3D shapes which causes them to have diverse chemical properties Enzymes are proteins that catalyze (speed up) chemical reactions Some proteins binds DNA while others bind other proteins such as motor, receptors, etc. Genetics Day 2 Blended inheritance idea is incorrect Idea that genes blend together to create something new such as a red and white flower creating a red white or pink flower Genes don’t work like this Mendel inheritance is correct Why was he successful? He used a good model organism (peas) because you can grow a large number of them very quickly There are several varieties of peas and plants They can cross AND self-fertilize He examined discontinuous character traits Two distinct phenotypes (how they look) Wrinkled vs unwrinkled, yellow vs green, etc He used true breeding strains (only contain all dominant or all recessive genes) This means that if self-fertilized then all generations would be the same He quantified data Wrote down generations P (or F0) for parents, F1 for first generation, F2 for second generation, etc. He built models to explain his data Alleles Dominant are capitalized and recessive are lowercase letters Examples: RR and Rr are round peas and rr is wrinkled peas RR or rr are known as homozygous while Rr is heterozygous RR x rr (which are pure-breeding parents) Rr (which is F1) (Self cross F1) Rr x Rr RR, Rr, and rr (this is F2 generation) 25% offspring rr, 25% RR, and 50% Rr. Phenotypically though 25% are wrinkled and 75% are round Mendels first law Adults have 2 versions of each gene Gametes receive 1 gene from each parents Must be true for Mendel’s first law to be true Character trait specified by a single gene Adult organisms must have 2 copies of each gene Gametes have only 1 copy of each gene Segregation of alleles are governed by law of chance The reason some alleles are dominant and others are recessive is because DNA sequence changes in recessive alleles to inactivate an encoded protein when a dominant allele is around Only one functional allele and that is dominant (only need one dominant allele for it to show up) This is called haplosufficient The recessive allele is heterozygotes is not functional Special cases of incomplete dominance have intermediate In the case of some flowers you can have red and white, cross them, and attain some pink flowers (doesn’t happen often) Genetics day 3 What accounts for mendels law? 2 alleles per gene Humans have 23 pairs of chromosomes (half from mom and half from dad) 2n=46 Chromosomes made of DNA, genes are part of DNA, and alleles are what make up genes Two types of cells in the body Somantic cells (diploid number of chromosomes (2 chromosomes) normal functions aka mitosis) Gametes (haploid (one chromosome) sex cells like sperm and eggs aka meiosis) Most cells are diploids, only a minority of cells are gametes 2 copies of each chromosome and 2 copies of each gene Haploids are half of that Cells replicate DNA in S phase Phases are: M, G1, S, G2 Phases in M phase are: Interphase, prophase, metaphase, anaphase, and telophase Cell division needs movement of chromosomes Interphase DNA is not compacted, Prophase DNA compacts, Metaphase chromosomes are pulled towards the middle, anaphase chromosomes are pulled towards opposite poles, and telophase the cell splits in two How does mitosis make sure that all of the daughter cells are genetically identical? Cells have to replicate DNA (S phase) prior to cell division (M phase) 1 DNA double helix is a chromatid and 2 are chromosomes Centromeres are in the middle of chromosomes to help hold them together Homologous chromosomes are similar and come from the parents Sister chromatids are identical Separation of sister chromatids ensures each new cell will receive one copy of each homolog Cytokinesis is actual splitting of cell and cytoplasm Meiosis reductional division In meiosis 1 homologs separate and in meiosis 2 sisters separate Aneuploidy A problem with division that results in an abnormal amount of chromosomes Can happen in meiosis 1 or 2 There are many possible reasons why aneuploidy occurs such as an error in attaching spindle to centromere Some diseases due to aneuploidy are downs syndrome, tay sachs disease, etc. Concept of gene dosage Much of the time proteins work together and this requires a certain amount/stoichiometry of components If chromosomes are gained or lost, then this upsets the balance of dosage which is thought to create stress on the systems at play Depending on how many genes this affects determines how large of a problem this causes