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Heredity Biology 30 Chapter 18.1 Early Theories of Inheritance Aristotle (384-322 B.C.E.) proposed the first widely accepted theory of inheritance • called pangenesis • egg and sperm consist of particles called pangenes that come from all parts of the body. • upon fertilization the pangenes develop into the parts of the body from which they are derived. Antony van Leeuwenhoek (1632-1723) discovered sperm in semen. • • he believed he thought he saw a complete miniature person called a homunculus inside the head of the sperm. other people of Antony’s time thought that the egg contained the entire person. Mendelian Genetics Gregor Mendel (1822-1884) a Augustinian monk in Brunn (Czech Republic), Austria his research laid the foundation for modern genetics and the science of inheritance. for seven years he bred pea plants (Pisum sativum) and analyzed the results. Gregor Mendel Mendelian Genetics Mendel focused on seven different traits of pea plants.. Mendelian Genetics Mendel let plants self-pollinate to ensure they were true breeding. • true breeding plants exhibit the same characteristics generation after generation. • Mendel called • true breeding plants the parental or P generation • the first offspring first filial or F1 generation • If the F1 generation were to pollinate the offspring would be called the second filial or F2 generation Mendelian Genetics • because all of Mendel’s initial crosses only involved • one trait we call them monohybrid crosses. Mendel observed that: • for every trait crossed the F1 generation only showed one of the two parental traits. ie. if plants with round seeds were crossed with plants of wrinkled seeds the F1 generation would only have plants of round seeds. Mendelian Genetics • even though the F1 generation had a copy of both genes only one was expressed. • Mendel called this characteristic dominant. allele: one of alternative forms of a gene. the gene for wrinkled and the gene for round peas are alleles. Mendelian Genetics dominant trait: a characteristic that is expressed when one or both alleles in an individual are the dominant form ~ dominant alleles are indicated by an uppercase letter (R) Mendelian Genetics • Mendel called the characteristic that was not expressed recessive recessive trait: a characteristic that is expressed only when both alleles in an individual are the recessive form. • Mendel concluded that one form showed complete dominance. • an individual with one dominant and one recessive (Rr) had the same characteristics as one with two dominant forms (RR) Mendelian Genetics Mendel’s Traits Trait Dominant Recessive Stem Length Tall (T) Short (t) Pod Shape Inflated (I) pinched (i) Seed Colour Yellow (Y) Green (y) Flower Position Axial (A) Terminal (a) Flower Colour Purple (P) White (p) Seed Shape Round (R) Wrinkled (r) Pod Colour Green (G) Yellow (g) Mendelian Genetics Important Definitions Homozygous: having identical alleles for the same gene Heterozygous: having different alleles for the same gene. Genotype: the genetic complement of an organism Phenotype: the observable characteristics of an organism Segregation: the separation of alleles during meiosis. Mendelian Genetics Law of Segregation Mendel’s First Law • All individuals have two copies of each factor (gene). These copies segregate (separate) randomly during gamete formation, and each gamete receives one copy of every gene. in 1909 Danish Botanist Wilhem Ludwig Johannsen called Mendel’s “factors” genes Mendelian Genetics Analyzing Genetic Crosses Reginald Punnett (1875-1967) • devised a visual way to analyze the results of crosses, called a Punnett’s square. Mendelian Genetics Punnett Squares •are used to predict the genotype and phenotype of potential off-spring •very useful when producing economically important cattle and plants. P Generation ♀ ♂ Phenotypic Ratio Genotypic Ratio Mendelian Genetics Trait Dominant Phenotype Genotype(s) Recessive Phenotype Genotype(s) Short tt (homozygous) Pinched ii (homozygous) Wrinkled rr (homozygous) White pp (homozygous) TT (homozygous) Stem Length Tall Tt (heterozygous) II (Homozygous) Pod Shape Inflated Ii (hetorozygous) RR (Homozygous) Seed Shape Round Rr (Heterozygous) PP (Homozygous) Flower Colour Purple Pp (herozygous) In order to see recessive phenotypes the genotype must be homozygous Now… Do your ears hang low activity Homework: Journal questions http://bussongs.com/assets/midi/DoYourEarsHangLow.mp3