GeneticsSlide 2Some Older, Incorrect TheoriesMore Ancient IdeasMendelMendel’s Basic InnovationsMendel’s ExperimentsExamining One TraitExplanation and VocabularyMore ExplanationSlide 11Still More ExplanationCross SummaryBack CrossComplications: Variations in DominanceCo-dominanceSingle Genes Can Have Multiple EffectsLethal GenesMore on Lethal GenesEnvironmental EffectsTwo Genes Affecting One TraitContinuous VariationIndependent AssortmentLinkageSome Common Genetics DiseasesSickle-cell DiseaseMalaria vs. Sickle Cell DiseaseCystic FibrosisPhenylketonuriaSome Dominant TraitsMarfan SyndromeRetinoblastomaSchizophrenia: a Complex Genetic TraitMore SchizophreniaGeneticsGenetics•A few facts about inheritance known since ancient times:– children resemble their parents. –Domestication followed by selective breeding to improve plants and animals. Mostly 10-12,000 years ago.–Some lines are true-breeding, others have a variety of offspring types. Different breeds can be produced through selective breeding.Some Older, Incorrect Theories•Hippocrates, an ancient Greek, taught the idea of pangenesis, that inheritance comes from the presence in each organ of tiny replica organs. These replicas moved through the blood to the semen, where they formed a tiny human which grew in its mother’s womb. Problem: if you cut off someone’s arm, their children still have arms.•Preformation is the idea that each sperm contains a miniature person: development is merely a process of enlarging and maturing the person already present in the sperm cell. There is another version of this theory that puts the miniature person in the egg instead of the sperm.•Inheritance of acquired characteristics. The idea that events that occur in your life affect your offspring directly. For instance, constant stretching of the giraffe’s neck made its offspring’s neck longer. Often associated with Lamarck, but the idea is much older.More Ancient Ideas•Relative contribution of male and female. Many cultures believed that the child grew from the semen, with the female’s role merely to act as a source of nutrition, like planting a seed in the garden. Also, allegedly some New Guinea cultures didn’t know that sex was necessary for reproduction, which implies the female was the sole source of the child.•Blending inheritance. Like mixing red paint with white paint: the results is pink paint, and there is no way to ever separate out the red and white. •Plants and sex. Although it was known to many ancient cultures, the idea that all plants have male and female parts wasn’t widely accepted until the early 1700’s.Mendel•Gregor Mendel lived in what is now the Czech Republic (then part of the Austria-Hungarian Empire) from 1822 to 1884•After high school he became a monk. The monastery sent him to the University of Vienna.•After college he did plant hybridization experiments in the monastery garden, growing more than 28,000 pea plants between 1856 and 1863.•Wrote up the work as “Experiments on Plant Hybridization” in a local scientific journal, where it was promptly forgotten. In those days, Darwin’s work was stirring controversy. Darwin had an incorrect notion of genetics: evolution was reconciled with genetics in the 1930’s, in the “modern synthesis”.•Mendel was elected abbot and gave up his studies, dying in 1884. •In 1900, 3 scientists working on plant breeding independently found his paper, read it, and understood how it explained their own work: the “rediscovery” of Mendel. This is the start of modern genetics.Mendel’s Basic Innovations•Inheritance is particulate: genes are not blended together, even if the effects of the genes get blended. For instance, in some plants if you cross a red flower with a white flower, the offspring have pink flowers. But, if you then cross 2 of the pink flowers together, the next generation has some red flowers and some white flowers, unchanged by having been in a pink parent. •Counting offspring, and seeing experimental numbers as imperfect reflections of underlying simple ratios. As an example, if you flipped a coin 1000 times you might get 477 heads and 523 tails. This represents a 1:1 ratio that contains a small amount of random error.Mendel’s Experiments•He worked with pea plants. Peas have male and female parts all within one flower. You can take the pollen (male gamete, equivalent to sperm) and put it on the pistils (female structures) of another plant, where it fertilizes the ovule (female gamete) to form a zygote, the first cell of the next generation.•Peas can self-pollinate (or “self”): the male pollen can fertilize the female ovule within a single plant. This is the closest possible genetic relationship. •He worked with true-breeding lines: all peas within the line looked similar.•He started with 7 different true-breeding lines, which differed for 7 distinct characters.Examining One Trait•Start with flower colors: one line has purple flowers, another line has white flowers. These two lines are called the “P generation”, for parental. When crossed, their offspring are the F1 generation. All of the F1 offspring are purple. Purple is called the dominant trait, because it is expressed in the F1 offspring. White is recessive, not expressed in the F1 offspring.•When the F1 plants are self-pollinated (or crossed with each other), their offspring are the F2 generation. The F2 are the grandchildren of the P generation. The F2 were found in a ratio of ¾ purple to ¼ white.•The same effects were seen for all 7 traits: if two lines are crossed together, the F1 all look like one of the parents, and the F2 are ¾ like one parent (the dominant trait) and ¼ like the other parent (the recessive trait).Explanation and Vocabulary•Genes are the factors that control the inherited traits. Genes are made of DNA; they are part of the chromosomes.•Individual versions of a gene are called alleles. Here, the flower color gene has two alleles: a purple allele and a white allele. •Pea plants (and humans and most higher organisms) are diploid: they have 2 copies of each gene, one from each parent. The gametes (sperm and egg, or pollen and ovule) are haploid: only 1 copy of each gene. •When the sperm fertilizes the egg, the two haploid genomes mix, forming a new diploid, which is the zygote, the first cell of the offspring. •The true breeding purple line produces only pollen carrying the