Lecture 16 Outline of Last Lecture I. Types of ReproductionII. Sexual ReproductionIII. MeiosisIV. Mitosis vs. MeiosisV. Sources of Genetic VariationOutline of Current Lecture I. History of GeneticsII. Background of Mendel’s ExperimentsIII. Mendel’s ExperimentsIV. Mendel’s Law of SegregationV. Mendelian Genetics VocabularyVI. Mendel’s Experiments Interpreted Using Modern Terminology (Punnett Squares)VII. Mendel’s Law of Independent AssortmentVIII. Human GeneticsCurrent LectureChapter 14 – Mendelian GeneticsI. History of Geneticsa. Aristotle  pangenesisi. Pangenes come from all parts of the body to make egg and spermb. 17th Centuryi. Spermists – little person in the sperm; females were only the incubatorii. Ovists – little person in the egg; sperm only stimulates the growth of the personc. Modern Genetics  Gregor Mendeli. 1860ii. Augustan monkiii. Figured out basics of genetics BIOL 1st EditionII. Background of Mendel’s Experimentsa. Methods  garden peas were experimental organismsi. Easy to growii. Strict control over matingiii. Easily distinguished varietiesb. Termsi. Character – heritable feature (today known as genes)ii. Trait – each character occurs in 2 variant forms, which Mendel called traits (today knownas alleles)c. 7 characters to study, each with 2 variant formsi. pod color (character)  green or yellow (traits)d. Each character had “true-breeding” plantsi. If the plant was self-fertilized, the offspring ALWAYS had the parental traitsIII. Mendel’s Experimentsa. Began with crosses between parent plants that only differed from the other with ONE trait  monohybrid crossb. Example: P1  true breeding GREEN pod x true breeding YELLOW podi. F1  all offspring had GREEN pods1. F2 (self-fertilized)  green pods/yellow pods (3:1 ratio)c. All 7 characters had similar resultsd. F1 generation always had offspring with only ONE of the 2 traitse. F1 self-fertilized generation would always had the second trait reappear in a 3:1 ratiof. Trait was not lost, just masked by the dominant traitIV. Mendel’s Law of Segregationa. Inheritable features (characters/genes) exist in two forms (traits/alleles)b. Organisms have 2 copies of each character, and one of those is inherited from each parentsc. The two copies segregate (separate) in the gametes (each gamete gets only one or the other) and recombine in the zygote (first cell of new offspring)i. Egg gamete (1N) & sperm gamete (1N)  zygote (2N)d. One trait (allele) is dominant over the otheri. The dominant allele is always seen (even if only one copy is present)ii. The other allele is called the recessive allele, that trait is only seen if both copies are the recessive copiesV. Mendelian Genetics Vocabularya. Genotype – what genes (and alleles of those genes) are present, aka the genetic makeup of an individual b. Phenotype – what an individual looks like (which traits are expressed)c. Dominant alleles are given a name indicated as a capitol letter, while recessive alleles are given the same name, but indicated with a lower case letteri. Green pod allele = dominant form = Gii. Yellow pod allele = recessive form = gd. All individuals get two copies of each because they are diploid (2N)i. Homozygous dominant = both copies are the dominant alleleii. Homozygous recessive = both copies are the recessive alleleiii. Heterozygous dominant = one dominant and one recessiveiv. Example: Pod colorGenotype Phenotype GametesGG Green All have G allelegg Yellow All have g allelesGg Green½ have G½ have gVI. Mendel’s Experiments Interpreted Using Modern Terminology (Punnett Squares)a. P1  true breeding GREEN pod (GG) x true breeding YELLOW pod (gg)i. F1  all offspring had GREEN pods (heterozygous Gg) , shown with Punnett Square (Parent 1 was GG and Parent 2 was gg)G Gg Gg Ggg Gg Gg1. F2 (self-fertilized)  green pods (Gg, GG)/yellow pods (gg) (3:1 ratio)¼  GG; ¼  gg, ½ Gg *gives a 3:1 ratio of green pods:yellow podsGg AND GG are green; gg is yellowG g G GG Ggg Gg ggVII. Mendel’s Law of Independent Assortmenta. How do alleles sort out during a dihybrid cross – differed with regard to 2 different traitsb. Two traits segregate independently of each otherc. Today we know that independent assortment is due to independent assortment of homologous chromosome pairs during meiosisd. This “Law of Independent Assortment” is only true when the traits being examined are on different chromosomesi. Example: G  Green pods, g  Yellow pods; R  round seeds, r  wrinkled seedsGametes can be one of 4 ways: GR, Gr, gR, and grGR Gr gR grGR GGRR GGRr GgRR GgRrGr GGRr GGrr GgRr GgrrgR GgRR GgRr ggRR ggRrgr GgRr Ggrr ggRr ggrrPhenotypic Ratio:9: green, round3: green, wrinkled3: yellow, round1: yellow, wrinkledVIII. Human Geneticsa. Humans are not good organisms for genetic experimentsi. Generation time is longii. Few offspringiii. Social constraints (can’t do breeding experiments)b. To study human genetics, family pedigrees are used  the results of mating that has already occurredc. Two kind of genetic disorders:i. Dominantii. Recessived. Recessive Disorders:i. More common that dominantii. Detrimental allele can be carried by an individual without being expressed (recessive)iii. In a cross between 2 heterozygous individuals:1. ¼ will be homozygous2. ½ will be heterozygous (carriers)3. ¼ will be homozygous (show the disorder)iv. Recessive disorders that are lethal before reproduction age, it tends to be rare because the carrier won’t reproducev. Examples:1. Cystic Fibrosis – excessive mucus in lungs; lethal before 5 if not treated; 1/2,500 are Caucasian2. Tay-Sachs disease – brain unable to metabolize lipids properly; lethal before 6 years old; 1/3,600 Central European Jews3. Sickle Cell Anemia – altered hemoglobin (protein that carries O2 in blood); red blood cells take on a shape like a sickle and get caught in the capillaries; despite this detrimental phenotype in homozygous individuals, the allele is maintained athigh levels in the African American population (~11,500 have it, 1/10 carry it)a. Pleiotrophy – sickle cell allele affects more than one traitb. Confers sickle cell disorder when homozygous, but also confers resistance to malariac. Resistance to malaria occurs even when the allele is heterozygousd. Malaria is a serious disease in Africae. AA  no sickle cell disorder, but die of malaria; Aa  ADVANTAGE, resistant to malaria, DO NOT show