Genetics Week One
Genetics Week One BIO3010
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This 10 page Class Notes was uploaded by Samantha on Wednesday January 20, 2016. The Class Notes belongs to BIO3010 at University of Toledo taught by Dr Krishnamurthy in Winter 2016. Since its upload, it has received 23 views. For similar materials see Genetics in Biology at University of Toledo.
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Date Created: 01/20/16
Genetics: Approaches for Studying Genetics o Transmission genetics Examination of the patters of inheritance of traits Classical or Mendelian genetics Experiments designed dot follow the transmission of traits from parents to offspring though several generations o Molecular Genetics The use of molecular, cellular, and biochemical techniques to study the transfer of genetic information Gene expression- transcription and translation DNA replication, repair, and recombination o Population Generics Studies on the frequencies at which various alleles and genotypes occur in a population and how theses frequencies change from one generation to the next Nucleus stores genetic info o Nucleic acids are the hereditary material o What is a gene? A specific functional unit of the DNA (or RNA) coding for RNA of protein Bacteria has about 1000 genes Plants have about 3800 genes Yeast has about 6000 genes Humans have about 20000 genes Chromosome theory of Inheritance o Extrachromosomal Inheritance (cytoplasmic inheritance) Mitochondria and chloroplasts have DNA Central Dogma of genetics o DNA RNA Protein Mutation and Natural Selection o Different living species share same molecular mechanism Eg. Defect in the kit gene (required for development and maintenance of pigment cells) causes same phenotype in humans and mice Genotype and phenotype o Normal beta globin DNA…………...CTA mRNA…………GAG Amino Acid….glu o Mutant beta globin DNA………….…CAC mRNA…………...GUG Amino Acid…..glu Cells in same multi-cell organism can be different- even though they have the same set of genes o Eg. Blood cells vs nerve cells o Differential, temporal and spatial expressions of genes Recombinant DNA technonogy Model genetic systems o E.coli Prokaryote, small genome, single copy of all genes o Yeast Single celled eukaryote, small genome, haploid or diploid, culture like bcteria Genetics: Mendel’s Laws of Genetic Inheritance Mendel o Garden Pea Self-fertilizing, can be cross bred Reproduces well and grows quickly Several different contrasting traits that can easily be followed one generation to the next easily be followed from one generation to the next o Mendel’s monohybrid Cross Mate two individual pea plants with contrasting traits Ex) tall crossed with dwarf The original parents (P –1parental gene) are true-breeding Ex) during self-fertilization offspring always have same characteristics as the parent o Tall pants always produce tall offspring o Dwarf plants always produce dwarf offspring o Mendel’s seven monohybrid crosses Seven pairs of contrasting traits Results of monohybrid crosses of all seven contrasting traits result in a 3:1 ratio in the F2 (second cross) plants Note that in the F 1first cross) generation one of the traits disappears and reappears in the F ge2eration Reciprocal crosses produced the same results- results not sex – dependent o Proposed that unit factors exist for each trait These serve as the basic unit of heredity Passed on from generation to generation Determine the various traits expressed by each individual o Mendel’s first three postulates Unit factors exist in pairs Ex) tall/tall; tall/dwarf; dwarf/dwarf Dominance and recessive Two unlike factors (tall vs dwarf) for a single character o One is dominant to the other Trait in 1 is controlled by the dominant unit factor Trait not expressed is controlled by the recessive unit factor Segregation Segregation of the unit factors during gamete formation o Paired unit factors segregate randomly o Each gamete receives one with equal likely hood o Genetic terminology Phenotype The physical appearance of a trait o Ex) tall or dwarf; round or wrinkled Alleles Alternative forms of a gene o Phenotype is determined by which form (alleles) of a gene are present in an organism o Tall and dwarf phenotypes are determined by different alleles of the same gene Genotype o The actual genetic makeup of an individual Which alleles are resent in tan organism o Monohybrid cross It o Test Cross Used to determine the genotype of F gene2ation A tall plant can be either DD or Dd Cross organism expressing the dominant phenotype (but unknown genotype) to a homozygous recessive individual Further demonstrated that separate unit factors control traits If the tall plant is homozygous then ALL offspring will display dominant trait If the tall play is heterozygous then the test cross will give an equal number of tall and dwarf plants (1:1 ratio) o Dihybrid Cross 2-factor cross Simultaneously examine 2 pairs of contrasting traits Example: Pea plants with yellow and round seeds crossed with pea plants with green and wrinkled o F 1lants are all yellow and round o F 1elf-fertilizing F2plants 9/16 yellow. Round 3/16 yellow, wrinkled 3/16 green, round 1/16 green, wrinkled Product law of probability: When 2 independent events occur at the same time the combined probability of the two outcomes is equal tot eh product of their individual probabilities of occurrence F2plants 12/16 yellow; 4/16 green = 3:1 ratio 12/16 round; 4/16 wrinkled = 3:1 ratio o The two pairs of contrasting traits are inherited independently Allows the frequencies of F p2enotypes to be predicted o Mendel’s fourth postulate Independent assortment Segregation of any pair of unit factors occurs independently of all others Results of random segregation Each gamete receives 1 member of every pair of unit factors One pair does not influence the segregation of any other pair ALL possible combinations of gametes are formed with equal frequency o Dihybrid cross demonstration independent assortment Independent assortment- all four combinations will be formed with equal probability All gametes receive G or g and W or w results of dihybrid cross produce the 9:3:3:1 ratio KEY: know all possible gamete combination Know the haploid number 2 so 2 = 4 possible gamete combination o Dihybrid test cross Test cross- use to determine genotype of an individual that expresses a dominant trait If you know the phenotype you can determine the genotype by performing crosses to a homozygous recessive plant o Trihybrid (3-factor) cross Follows the same principle of segregation and independent assortment Expected results of a trihybrid cross can be predicted Like 3 separate monohybrid crosses Homozygous dominant parent crossed with a homozygous recessive parent o F 1eneration will all be heterozygous for each trait and phenotypically will express the dominant trait o F 1ill then produce 8 different gametes based on the principles of segregation and independent assortment o Mendel’s postulates st A) Unit factors in pairs (1 meiotic prophase) Illustrated correlation between the Mendelian postulates of (a) o Presence of genes located on homologous chromosomes and their behavior during meiosis First meiotic prophase- unit factors (genes) are in pars o Segregation of chromosomes- gametes will get 1 of each chromosome B) Segregation of unit factors during gamete formation (1 st meiotic anaphase) Homologs segregate during meiosis C) Independent assortment of segregating unit factors (follow many mitotic events) Non-homologous chromosome assort independent Sutton and Boveri: thought Mendel’s unit factors were chromosomes rather than genes- chromosomal theory of inheritance o Pedigree analysis
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