Intro to Mendelian Genetics What is genetics? What is genetics? • The science of heredity What is genetics? • The science of heredity • How traits are passed to offspring What is genetics? • The science of heredity • How traits are passed to offspring • Gene – A section of DNA that codes for a specific protein • Gene – The unit of heredity Gregor Mendel • Born in Czech Republic, settled in Austria • In 1842, entered monastery at age of 21, tended to a garden of peas Gregor Mendel • In 1851 he went to the U. of Vienna to study science and statistics • Returned to monastery to teach high school and study heredity through his peas. (OMG, this is like sooooo exciting! I can’t wait to hear what happens next. Seriously, I’m about to pea my pants!) Current thoughts in 1850 • Blended inheritance – Offspring are intermediate in appearance Current thoughts in 1850 • Blended inheritance – Offspring are intermediate in appearance • Ex: skin tone in humans Current thoughts in 1850 • Blended inheritance – Offspring are intermediate in appearance • Ex: skin tone in humans – Ink in water 1. Combined 2. Inseparable Current thoughts in 1850 • Blended inheritance – (Incorrect) – Offspring are intermediate in appearance • Ex: skin tone in humans – Ink in water 1. Combined 2. Inseparable Used peas to study inheritance • Why peas? Used peas to study inheritance • Each plant has various traits to study • Cheap • Simple to grow • Seeds easily stored for later study • Short generation time • Self-pollinators (flowers have male and female parts) • Cloned flowers can serve as control group Statistics was the key! • Used math to explain living systems (one of the first to do so) • Published his work in 1866, but mostly ignored because he didn’t know the mechanism of heredity (DNA) Mendel’s 1st Experiment • Studied 7 characteristics with two traits each • Plant height, flower color, etc. Mendel’s 1st Experiment • Studied 7 characteristics with two traits each • Plant height, flower color, etc. – Focus on plant height: • Tall or short: Mendel’s 1st Experiment • Studied 7 characteristics with two traits each • Plant height, flower color, etc. – Focus on plant height: • Tall or short: T or Mendel’s 1st Experiment • Studied 7 characteristics with two traits each • Plant height, flower color, etc. – Focus on plant height: • Tall or short: T or t Mendel’s 1st Experiment • Studied 7 characteristics with two traits each • Plant height, flower color, etc. – Focus on plant height: • Tall or short: T or t – All studied traits were heritable, not environmental – Used purebreds (clones) achieved through many generations of self-pollination Mendel’s 1st Experiment • Crossed a purebred tall with a purebred short – Paternal: T x t – Filial (F1): ?? Mendel’s 1st Experiment • Crossed a purebred tall with a purebred short – Paternal: T x t – Filial (F1): 100% tall (T) • Same result with all 7 characteristics • Trait that showed up in F1 generation = dominant • Disappearing trait = recessive Mendel’s 1st Experiment • Where did the recessive trait go? Mendel’s 1st Experiment • Where did the recessive trait go? • To find out, he self-pollinated the F1 plants – F1: T x T Mendel’s 1st Experiment • Where did the recessive trait go? • To find out, he self-pollinated the F1 plants – F1: T x T – F2: 75% T, 25% t Law of segregation • Law of segregation : Traits are discrete units that occur in pairs and retain their integrity Law of segregation • Law of segregation : Traits are discrete units that occur in pairs and retain their integrity • Characteristics are now called genes (one or more genes lead to the appearance of a certain characteristic) Mendelian Genetics Continued… • The location (address) of a gene on a chromosome is called the locus • Genes have alternate versions called alleles • ex: locus for flower color • Genotype: The collection of alleles in an individual – Represented by letters • Genotype: The collection of alleles in an individual – Represented by letters • P: TT x tt (T = dominant allele –> only one needed for expression) • F1: • Phenotype: • Phenotype: Physical expression of genotype + environment – Represented by • Phenotype: Physical expression of genotype + environment – Represented by descriptive words • F2 : Tt x Tt Genotypes: Phenotypes: Genotype terminology • TT = Homozygous dominant or purebred dominant • Tt = • tt = Genotype terminology • TT = Homozygous dominant or purebred dominant • Tt = Heterozygous dominant or hybrid • tt = Homozygous recessive or purebred recessive • How can you tell the difference between a homozygous dominant (DD) and a heterozygous dominant (Dd)? • How can you tell the difference between a homozygous dominant (DD) and a heterozygous dominant (Dd)? • Test Cross: Breed the unknown with a homozygous recessive to bring out any hidden recessive traits • Test Cross: Breed the unknown with a homozygous recessive to bring out any hidden recessive traits • Law #1: Law of segregation • Law #2: Law of independent assortment – Genes located at different loci (locations) on the same chromosome assort (cross-over) independently of each other • Law #1: Law of segregation • Law #2: Law of independent assortment – Genes located at different loci (locations) on the same chromosome assort (cross-over) independently of each other • (Whether one gene crosses over during meiosis has no influence over whether another gene on the same chromosome crosses over)