Transcript Slide 1
What is the point of meiosis and sexual reproduction? Agenda for Jan 22nd 1. Go over test 2. Punnett Squares Heredity • What is heredity? – The passing on of characteristics from parents to offspring • Genetics is the branch of biology that studies heredity – characteristics that are inherited are traits • Mendel was the first to succeed in predicting how traits would be transferred from one generation to the next Mendel • Father of genetics • Loved nature • Austrian monk – taught natural science – worked on plant breeding experiments using pea plants • Developed basic understanding of genetics and inheritance Mendel’s Work • Used pea plant • He collected data for 10 years • Large sample sizes; – Results from 28,000 pea plants • Published work but was dismissed – Found later Mendel’s Experiment • P Generation – parent generation • F1 generation – first filial generation, offspring of parents • F2 generation – second filial generation, offspring of F1 generation Grandparents Parents You Collected 6022 yellow and 2001 green 3:1 ratio Mendel’s Results P1 F1 F2 F2 ratio smooth X wrinkled seeds all smooth 5474 smooth 1850 wrinkled 2.96:1 yellow X green seeds all yellow 6022 yellow 2001 green 3.01:1 axial X terminal flowers all axial 651 axial 207 terminal 3.14:1 red X white flowers all red 705 red 224 white 3.15:1 882 inflated 299 constricted 2.95:1 all green 428 green 152 yellow 2.82:1 all tall 787 tall 277 dwarf 2.84:1 inflated X constricted pods green X yellow pods tall X dwarf plants all inflated 3:1 ratio Conclusions 1. Inheritance of traits are determined by "units" or "factors" that are passed on to offspring – called genes – Different forms of a gene are alleles Allele for purple flowers Locus for flower-color gene Homologous pair of chromosomes Allele for white flowers 2. For each trait, an individual inherits one gene from each parent 3. A trait may not show up in an individual but can still be passed on Rule of Dominance • The trait that is observed in the F1 offspring is the dominant trait (uppercase) • The trait that disappears in the offspring is the recessive trait (lowercase) Law of Segregation • The two alleles for a trait must separate when gametes are formed – A parent randomly passes only one allele for each trait to each offspring Law of Independent Assortment • Random distribution of alleles during meiosis Dominant and Recessive Genes • Gene that prevents the other gene from “showing” – dominant • Gene that does NOT “show” even though it is present – recessive • Symbol – Dominant gene – upper case letter – T Recessive gene – lower case letter – t Dominant color Recessiv e color Dominant and Recessive • Capital letters= dominant alleles • Lower case letters = recessive alleles • Two alleles for each trait Which is better, dominant or recessive? Homozygous (pure bred) Organism with two of the same allele HH Homozygous dominant hh Homozygous recessive Heterozygous (hybrid) Organism with two different alleles Hh Rr Dominant trait observed (notice the dominant allele) Genotype Allele makeup of an individual Tt RR TT Rr tt rr Phenotype Observable characteristics of an individual Flashcards • • • • • • • Phenotype Genotype Heterozygous Homozygous Allele Diploid Haploid Predicting traits • Monohybrid Crosses Provide information about one pair of contrasting traits. Parent’s Genotype Parent’s Genotype Law of Segregation • Mechanism of gene transmission Gametogenesis: alleles segregate Fertilization: alleles unite Parent’s 1 Genotype = Aa Gametes = Parent’s 2 Genotype = AA Gametes = Ratios: Genotypes: Homozygous dominant:Hetergozygous:Homozygous recessive AA:Aa:aa Phenotypes: Dominant:recessive Tall:short Define the following: Dominant, recessive, homozygous, heterozygous. Agenda for Friday Jan 23rd 1. Review 2. Punnett Square practice Practice A Tt (tall) plant is crossed with a Tt (tall plant). 1. What are the gametes formed by each parent? 2. What is the genotypic ratio? A green pea sead (gg) is crossed with a hybrid yellow seed (Gg). What will be the genotypic and phenotypic ratios of the offspring? A heterozygous plant (Tt) is crossed with short (tt) plant. What percentage of the offspring will be tall? What percentage of the offspring will be short? In guinea pigs, rough coats are dominant over smooth coats. An Rr guinea pig is crossed with an Rr guinea pig. What are the chances of each genotype and phenotype? Agenda for Tuesday April 15th 1. Punnett Square practice The punnett square shows the offspring of two parents. What are the genotypes of the parents? Rr Rr rr rr Agenda for Thursday April 17th 1. Compare ratio lab QUIZ WEDNESDAY In pea plants, round (R) is dominant to wrinkled (r). A heterozygous female is crossed with a wrinkled male. What is the probability (percent) of having an offspring that is round? Agenda for Tuesday April 22nd 1. Dihybrid crosses Quiz tomorrow Polyploidy • Most cells are Diploid (2n) • Some are polyploid – One or more extra sets of chromosomes – Triploid – 3n • Rarely occurs in animals • Mostly plants – Roughly 1 in 3 plants are polyploidy • Increased vigor and size Types of genetic crosses • Monohybrid – Mono = 1 – Cross looking at 1 trait • Dihybrid – Di = 2 – Cross looking at 2 traits – Traits are not linked (do not affect each other) – For example: round vs. wrinkled seeds and yellow vs. green seeds Dihybrid Cross Making gametes • Independent assortment – each allele distributes randomly with the other **more combinations than with a monohybrid RrYy Round (R) is dominant to wrinkled Yellow (Y) is dominant to green Cross a RRYy with a Rryy What would the gametes look like for a RrYy genotype? Agenda for Wednesday April 23rd 1. TEST Genetic Recombination • New combination of genes produced by crossing over and independent assortment Why is genetic recombination important? Gene Linkage • Genes on same chromosomes are said to be linked – Travel together during Meiosis • Not always true – crossing over occurs • Genes further apart cross over more frequently – Make chromosome maps based on that info. Chromosome Map • Map genes A, B, C, D – AB=3 – AD=4 – BD=7 AC=1 BC=2 CD=5 • Map genes A, B, C, D – AD = 25 – CD = 15 – BC = 20 AB = 30 BD = 5