BIOL 1st Edition Lecture 16 Outline of Last Lecture I Types of Reproduction II Sexual Reproduction III Meiosis IV Mitosis vs Meiosis V Sources of Genetic Variation Outline of Current Lecture I History of Genetics II Background of Mendel s Experiments III Mendel s Experiments IV Mendel s Law of Segregation V VI Mendelian Genetics Vocabulary Mendel s Experiments Interpreted Using Modern Terminology Punnett Squares VII Mendel s Law of Independent Assortment VIII Human Genetics Current Lecture Chapter 14 Mendelian Genetics I History of Genetics a Aristotle pangenesis i Pangenes come from all parts of the body to make egg and sperm b 17th Century i Spermists little person in the sperm females were only the incubator ii Ovists little person in the egg sperm only stimulates the growth of the person c Modern Genetics Gregor Mendel i 1860 ii Augustan monk iii Figured out basics of genetics II Background of Mendel s Experiments a Methods garden peas were experimental organisms i Easy to grow ii Strict control over mating iii Easily distinguished varieties b Terms i Character heritable feature today known as genes ii Trait each character occurs in 2 variant forms which Mendel called traits today known as alleles c 7 characters to study each with 2 variant forms i pod color character green or yellow traits d Each character had true breeding plants i If the plant was self fertilized the offspring ALWAYS had the parental traits III Mendel s Experiments a Began with crosses between parent plants that only differed from the other with ONE trait monohybrid cross b Example P1 true breeding GREEN pod x true breeding YELLOW pod i F1 all offspring had GREEN pods 1 F2 self fertilized green pods yellow pods 3 1 ratio c All 7 characters had similar results d F1 generation always had offspring with only ONE of the 2 traits e F1 self fertilized generation would always had the second trait reappear in a 3 1 ratio f Trait was not lost just masked by the dominant trait IV Mendel s Law of Segregation a 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 parents c 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 other i 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 copies V Mendelian Genetics Vocabulary a 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 letter i Green pod allele dominant form G ii Yellow pod allele recessive form g d All individuals get two copies of each because they are diploid 2N i Homozygous dominant both copies are the dominant allele ii Homozygous recessive both copies are the recessive allele iii Heterozygous dominant one dominant and one recessive iv Example Pod color VI Genotype Phenotype Gametes GG Green All have G allele gg Yellow All have g alleles Gg Green have G have g 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 G g Gg Gg g Gg Gg 1 F2 self fertilized green pods Gg GG yellow pods gg 3 1 ratio GG gg Gg gives a 3 1 ratio of green pods yellow pods Gg AND GG are green gg is yellow VII G g G GG Gg g Gg gg Mendel s Law of Independent Assortment a How do alleles sort out during a dihybrid cross differed with regard to 2 different traits b Two traits segregate independently of each other c Today we know that independent assortment is due to independent assortment of homologous chromosome pairs during meiosis d This Law of Independent Assortment is only true when the traits being examined are on different chromosomes i Example G Green pods g Yellow pods R round seeds r wrinkled seeds Gametes can be one of 4 ways GR Gr gR and gr GR Gr gR gr GR GGRR GGRr GgRR GgRr Gr GGRr GGrr GgRr Ggrr gR GgRR GgRr ggRR ggRr gr GgRr Ggrr ggRr ggrr Phenotypic Ratio 9 green round 3 green wrinkled 3 yellow round 1 yellow wrinkled VIII Human Genetics a Humans are not good organisms for genetic experiments i Generation time is long ii Few offspring iii Social constraints can t do breeding experiments b To study human genetics family pedigrees are used the results of mating that has already occurred c Two kind of genetic disorders i Dominant ii Recessive d Recessive Disorders i More common that dominant ii Detrimental allele can be carried by an individual without being expressed recessive iii In a cross between 2 heterozygous individuals 1 will be homozygous 2 will be heterozygous carriers 3 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 reproduce v Examples 1 Cystic Fibrosis excessive mucus in lungs lethal before 5 if not treated 1 2 500 are Caucasian 2 Tay Sachs disease brain unable to metabolize lipids properly lethal before 6 years old 1 3 600 Central European Jews 3 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 at high levels in the African American population 11 500 have it 1 10 carry it a Pleiotrophy sickle cell allele affects more than one trait b Confers sickle cell disorder when homozygous but also confers resistance to malaria c Resistance to malaria occurs even when the allele is heterozygous d Malaria is a serious disease in Africa e AA no sickle cell disorder but die of malaria Aa ADVANTAGE resistant to malaria DO NOT show symptoms aa sickle cell disease e Dominant Disorders i Much less common than recessive always expressed ii Examples 1 Dwarfism heterozygous individuals are dwarfs 1 in 10 000 people homozygous individuals die before birth 2 Huntington s Disease late acting disorder symptoms begin at 35 45 years old affects nervous system