Lecture 1 Midterm Exam Notes.docx

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Biological Sciences
Dan Riggs

BIOB11 – Lecture 1 - Chromosomes, Heredity, Meiosis and Recombination Vocabulary Diploid: Containing both members of each pair of homologous chromosomes, seen in most somatic cells. Diploid cells are produced from diploid parental cells during mitosis. Two copies of each gene. Haploid: Containing only one member of each pair of homologous chromosomes. Haploid cells are produced during meiosis as seen in sperm. (gametes are haploid sperm and egg donate only one) Allele: Alternate forms of the same gene. Genotype: Genetic composition of organism. Phenotype: Observable traits or morphology Dominant: “wildtype” RR Recessive: rr Meiosis: part of gametogenesis in which sperm and eggs are produced. Homologous Chromosomes: Paired chromosomes of diploid cells, each carrying one of the two copies of the genetic material carried by that chromosome. Bivalent (tetrad): The complex formed during meiosis by a pair of synapsed homologous chromosomes. Paired homologous chromosomes.(four) Recombinant DNA: Molecules containing DNA sequences from more than one source. Reciprocal genetic exchange: Reciprocal patterns of labelling on two non-sister chromatids is indicative of breakage and reunion of exchanged segments. Homozygous: both alleles are identical (eg: dominant). If dominant, generally the “wildtype” RR Heterozygous: alleles differ (one dominant, one recessive = Rr) Nulls: Homozygous recessive (rr). Generally associated with the”mutant” trait. Conduct a cross: sperm and eggs get together. This is easy to do in plants as many are self fertile and will do the work for you. Synaptonemal Complex (SC): A ladderlike structure composed of three parallel bars with many cross fibers. The SC holds each pair of homologous chromosomes in the proper position to allow the continuation of genetic recombination between strands of DNA. Segregation: disjunction Non-disjunction: improper segregation Down Syndrome or Trisomy 21: A chromosome complement that has one extra chromosome; ie. A third homologous chromosome (causing Down Syndrome) Autosomes: not a sex chromosome Brief History of Genetics (will not ask dates and names) -2013: many genomes are completely sequenced -“bioinformatics” comes of age The earliest studies revealed genes to be discrete factors that were retained throughout the life of an organism and then passed on to each of its progeny. Over the following century, these hereditary factors were shown to reside on chromosomes and to consist of DNA, a macromolecule with extraordinary properties. -Genome: the collective body of genetic information that is present in a species. -Most organisms are diploid 10.1 The Concept of a Gene as a Unit of Inheritance -In the 1860’s, Gregory Mendel was the start of the science of genetics. His goal was to mate, or cross, pea plants having different inheritable characteristics and to determine the pattern by which these characteristics were transmitted to the offspring. Mendel chose to focus on seven clearly definable traits, including height, seed color, and seed shape, each of which occurred in two alternate and clearly identifiable forms as the Dominant Allele and the Recessive Allele forms (eg: for the seed shape, the dominant allele = round (R) and the recessive allele = wrinkled (r)). - After several years of research, Mendel drew the following conclusions: 1. The characteristics of the plants were governed by distinct factors (or units) of inheritance, which were later termed genes. An individual plant possessed two copies of a gene that controlled the development of each trait, one derived from each parent. The two copies could be either identical to one another or nonidentical. Alternate forms of a gene are called alleles. For each of the seven traits studied, one of the two alleles was the dominant over the other. When both were present together in the same plant, the existence of the recessive allele was masked by the dominant one. 2. Each reproductive cell (or gamete) produced by a plant contained only one copy of the gene for each trait. A particular gamete could have either the recessive or dominant allele for a given trait, but not both. Each plant arose by the union of a male and female gamete. Consequently, one of the alleles that governed each trait in a plant was inherited from the female parent, and the other allele was inherited from the male parent. 3. Even though the pair of alleles that governed a trait remained together throughout the life of an individual plant, they became separated (or segregated) from one another during the formation of the gametes. This finding formed the basis of Mendel’s law of segregation. 4. The segregation of the pair of alleles for one trait had no effect on the segregation of alleles for another trait. A particular gamete, for example, could receive a paternal gene governing seed color and a maternal gene governing seed shape. This finding formed the basis of Mendel's Law of independent assortment. - Mendel: Following the round vs wrinkled seed phenotype  10.2 Chromosomes: The Physical Carriers of the Genes The Discovery of Chromosomes: - All the genetic information needed to build and maintain a complex plant or animal had to fit within the boundaries of a single cell. - During cell division, the material of the nucleus became organized into visible “threads,” which were named chromosomes, meaning “colored bodies.” - Even though the sperm is a tiny cell, it was known to be as important genetically as the much larger egg. - The most apparent feature in common between both the egg and the sperm were the nucleus and its chromosomes. - Theodore Boveri: a Sea urchin egg had been fertilized by two sperm rather than just one, as is normally the case (this is called polyspermy and is characterized by disruptive cell division and early death of the embryo. -
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