350 likes | 551 Views
MENDELIAN GENETICS. OBJECTIVES. Understand Mendel’s principles governing genetics Understand meaning of relevant vocabulary Predict results of mono/dihybrid crosses using Punnett square Know exceptions to rules . GENETICS. Genetics: Heredity:. Gene (Character): Locus (loci= pl.):
E N D
OBJECTIVES • Understand Mendel’s principles governing genetics • Understand meaning of relevant vocabulary • Predict results of mono/dihybrid crosses using Punnett square • Know exceptions to rules
GENETICS • Genetics: • Heredity:
Gene (Character): Locus (loci= pl.): Allele (Trait): Genotype: Phenotype: GENETICS TERMINOLOGY
MENDEL • Gregor Mendel • Interested in basic patterns governing the transmission of traits from parent to offspring • Mendel’s work precedes an understanding of meiosis/genes/chromosomes
HISTORICAL HYPOTHESES REGARDING INHERITANCE Blending Inheritance Hypothesis: Inheritance of Acquired Characteristics Hypothesis
MENDEL • Mendel performed crosses between pure bred garden peas • Began studying inheritance of ONE trait • Later, multiple traits studied together
MENDEL’S CROSSES • Mendel's plants had twoobservable“forms” (alleles) of each “character” (gene) • Green or Yellow seeds • Round or Wrinkled seeds
Forms of Trait (Phenotype) Trait or Seed shape Round Wrinkled Round Wrinkled or Seed color Green Yellow Yellow Green Pod shape or Constructed Inflated Smooth Constricted or Pod color Yellow Green Green Yellow
Trait Forms of Trait (Phenotype) Flower color or Purple White White Purple Flower and pod position or Axial (on stem) Terminal (at tip) Axial (on stem) Terminal (at tip) Stem length or Dwarf Tall Tall Dwarf
MENDEL • Looked at traits exhibited by progeny of crosses • Found observableevidence of how parents transmit traits to offspring
MENDEL’S PEA PLANTS • Pisum sativum
Male parts = anthers • Pollen grain contain sperm • Female parts = pistil • Ovule = eggs SELF FERTILIZATION Stigma (receives pollen) Anthers (produce pollen grains, which contain male gametes) Ovules (produce female gametes)
MENDEL’S PEA PLANTS Controlled Mating: • Cut off reproductive organ to stop self fertilization • Cross fertilize plants in a controlled fashion • Plant that contributes pollen • Plant that receives the pollen
CROSS-POLLINATION 1. Remove anthers from one plant. 2. Collect pollen from a different plant. 3. Transfer pollen to stigma of the 1st plant (plant without anthers)
MENDEL’S CROSSES Round Parent x WrinkledParent
MENDEL’S CROSSES Round x Round (F1) Next, Mendel crossed F1 (bro-sis mating):
MENDEL’S CROSSES Mendel Determines (Phenotypic) Ratio: F2: 5474 Round : 1850 Wrinkled • Similar pattern observed in other 6 traits
MENDEL’S SYMBOLS • Mendel assigned symbols to hereditary characters • Letters represent versions of a gene (alleles): • Ex: If Letter “r” represents a gene then:
PUNNETT SQUARE • R.C. Punnett • Leading geneticist in early 1900s • Invented technique called the “Punnett Square” • Place gamete possibilities for 2 parents along axes • Internal boxes represent union of gametes • Used to predict genotype and phenotype of potential zygote
MENDEL’S CROSS OF PURE LINE PEA PLANTS PARENT: R R R is round r is wrinkled PARENT: r r ** hint: gametes along top, “whole people” on inside
MENDEL’S CROSS OF F1 PLANTS Crossing the F1s: Rr x Rr R = round r = wrinkled • Phenotypic Ratio: • Genotypic Ratio
Three possible genotypes for each gene in a diploid cell: Homozygous: Homozygous Dominant: Homozygous Recessive: Heterozygous: POSSIBLE GENOTYPES
PROBABILITY THEORY In Diploid Organisms, • Each allele has 50% chance of being found in a particular gamete • To calculate likelihood of two alleles combining (i.e. fertilization):
MENDEL’S CROSSES • Dihybrid Crosses: • Mendel used pea plants to follow inheritance of TWOtraits • Another pattern began to emerge…
MENDEL’S SYMBOLS • Seed Shape: • R is dominant allele (Round) • r is recessive allele (Wrinkled) • Seed Color: • Y is dominant allele (Yellow) • y is recessive allele (Green)
F2 OFFSPRING FROM DIHYBRID CROSS F2 generation phenotype Mendel’s Numbers 315 101 108 32 = 556 Fraction of progeny 9/16 3/16 3/16 1/16 = 1 Note: New mixtures of traits are observed in F2!!
PUNNETT SQUARE FOR TWO TRAITS Do genes segregate into gametes together or independently?
PUNNETT SQUARE FOR TWO TRAITS If genes segregate independently of each other, we end up with
MENDEL’S LAW OF INDEPENDENT ASSORTMENT • Law of Independent Assortment:
INDEPENDENT ASSORTMENT During meiosis I, homologs can line up two different ways before separating. Brown eyes Blue eyes OR Black hair Red hair
THE TEST CROSS • To determine genotype of an individual
MENDEL Why Mendel Was Successful: • Unbiased • Selected good model organism • Used pure breeds as parents • Large sample size • Quantitative analysis • Controlled experiments • Studied obvious traits