2 What is genetics?Genetics, a branch of biology, is the scientific study of heredity and variation of organisms.Gregor Mendel, an Austrian monk who studied botany. He made important progress in understanding heredity.Mendel studied the traits of ordinary garden peas.During Mendel’s time, the belief was that the traits of the parents blended.
3 Gregor Mendel’s work with plants Most plants have female and male parts on the same flower.**Male part of the flower produces pollen (sperm).**Female part of the flower produces ova (eggs)
4 Gregor Mendel’s work with plants Plants reproduce sexually.Pollen (male gamete) and ovum (female gamete) join making a new diploid cell.Fertilization produces a new diploid cell.Two options for the same flower:Self-pollinating: pollen and ovum come from the same flower.Cross-pollinating: ovum on one flower and pollen from flower on a different plant..
5 Mendel’s peas Mendel had pea plants that were true breeding. Seed from purple flowered plants had only purple flowered offspring.True breeding plants are ones that produce offspring like themselves.Mendel experimented with cross pollination between different parents.
6 Gregor Mendel’s work with peas A trait is a specific observable characteristic that varies from one individual to another.Seven traits of peas studied by Gregor Mendel: dominant version of trait is on the left, recessive on the right.
7 Crossing different pea plants P = parental generationF1 = first filial generation (offspring or children)F2 = second filial generation (grandchildren)Mendel’s Cross pollinationP two different parents, example: trait = height; alleles = tall or shortF1 offspring are all heterozygous plants. He used F1 as parentsHeterozygotes have different alleles.Homozygotes have the same alleles.F2 ‘grandchildren’ have ratios of 3 out of 4 dominant trait or 75% and 1 out of 4 recessive trait or 25%.
8 Mendel—Father of Genetics Mendel’s application of scientific method and mathematics to heredity in peas led to his discovery of ‘factors’.Mendel concluded that biological inheritance is determined by factors passed from one generation to the next.Today, scientists call the factors that determine traits genes.
9 Mendel—Father of Genetics Each trait that Mendel studied was controlled by one gene that occurred in two contrasting forms.The different forms of a gene are called allelesExample—trait is flower colorGene controls flower colorTwo forms are purple and whiteAlleles are P-purple, p-white
10 Mendel and his work Mendel predicted: The role of genes in heredity Alleles for a gene occur in pairs for an organismOne allele for a gene is in each gameteMendel had three key concepts:DominanceSegregationIndependent Assortment (Day 3)
11 Two of Mendel’s Principles 1. Law of Dominance:One allele does the ‘talking’. One allele is expressed. One allele was dominant over the other in the F1 generation.2. Principle of Segregation:When gametes are formed, the pairs of hereditary factors (alleles) become separated. Each sex cell (egg/sperm) receives only one version of the gene.3. Principle of Independent Assortment:Day 3 (Hint: multiple chromosomes divide in meiosis)
12 Gregor Mendel’s ideasMendel observed that some traits appeared to dominate.Dominant allele of gene is always expressed in classic Mendelian genetics.Other traits skipped a generation. Recessive trait.A trait is an observable characteristic that varies between individuals.Mendel counted the results of cross pollination. He calculated the probability of outcomes from his hypothesis.Probability is how likely something will happen. Mendel assumed the forms of a trait happened as random events with equally likely probabilities.Consider flipping a coin. Two equally likely outcomes.
13 Using a Punnett SquareSTEPS: 1. determine the genotypes of the parent organisms 2. write down your "cross" (mating) 3. draw a Punnett squareParents are tall and short. Parent genotypes:TT and t tCrossT T t t
14 Punnett square T T t T T t t T t 4. "split" the letters of the genotype for each parent & put them "outside" the p-square5. determine the possible genotypes of the offspring by filling in the p-square6. summarize results (genotypes & phenotypes of offspring)T TT T t tT ttGenotypes:100% T tPhenotypes:100% Tall plants
15 Monohybrid cross: F2 generation If you let the F1 generation self-fertilize, the next monohybrid cross would be:T t T t(tall) (tall)Genotypes:1 TT= Tall2 Tt = Tall1 tt = dwarfGenotypic ratio= 1:2:1Label your ratio TT:Tt:ttT tT TT tt tTtPhenotype:3 Tall1 dwarfPhenotypic ratio= 3:1Label your ratios tall: short
16 Secret of the Punnett Square Key to the Punnett Square:Determine the gametes of each parent…How? By “splitting” the genotypes of each parent:If this is your crossT T t tThe gametes are:TTtt
18 Another example: Flower color For example, flower color:P = purple (dominant)p = white (recessive)If you cross a homozygous Purple (PP) with a homozygous white (pp):P P p pALL PURPLE (Pp)P p
19 Cross the F1 generation: P p P pGenotypes:PPPp1 ppPpP PP pp pPPhenotypes:3 Purple1 Whitep
20 Stations Each group will visit all stations. Station 1—Vocabulary A Station 2—Punnett SquaresStation 3—Analysis of Punnett Square for ParentsStation 4—Vocabulary BStation 5—SegregationStation 6—Phenotype/GenotypeUse your handout to record your work at each station.
21 ResourcesDr. Dennis O’Neill, 2013, Basic Patterns of Genetics, Palomar CollegePaul Anderson, 2013, Mendelian Genetics, Bozeman Science,CrashCourse, 2013, Heredity, Crash Course in Biology,Staff, 2013, Glossary of Terms, Palomar College,