1Chapter 9 Objectives Section 1 Mendel’s Legacy Describe how Mendel was able to control how his pea plants were pollinated.Describe the steps in Mendel’s experiments on true-breeding garden peas.Distinguish between dominant and recessive traits.State two laws of heredity that were developed from Mendel’s work.Describe how Mendel’s results can be explained by scientific knowledge of genes and chromosomes.
2Section 1 Mendel’s Legacy Chapter 9Gregor MendelThe study of how characteristics are transmitted from parents to offspring is called genetics.Mendel is considered to be the “father” of genetics because of all of his work with heredityHeredity is the passing of traits from parents to their offspring
3Gregor Mendel, continued Section 1 Mendel’s LegacyChapter 9Gregor Mendel, continuedMendel’s Garden PeasMendel observed characteristics of pea plants.Traits are genetically determined variants of a characteristic.Each characteristic occurred in two contrasting traits.
4Gregor Mendel, continued Section 1 Mendel’s LegacyChapter 9Gregor Mendel, continuedMendel’s MethodsSelf-pollination occurs when pollen is transferred from the anthers (male) of a plant to the stigma (female) of the same plantCross-pollination occurs when pollen is transferred between flowers of two different plantsMendel controlled his experiments by manually pollinating the other plants through cross-pollination, he removed anthers from the plants he was working with
5P F1 F2 Chapter 9 Mendel’s Experiments Section 1Chapter 9PMendel’s ExperimentsF1F2Mendel bred plants for several generations that were true-breeding (self-pollinating) for specific traits and called these the P generation. (parental)True breeding pea plants always produce offspring each of which can have only one form of a traitEx. True-breed pea plants with yellow pods will self-pollinate and produce offspring with yellow podsOffspring of the P generation were called the F1 generation.Offspring of the F1 generation were called the F2 generation.
6Three Steps of Mendel’s Experiments Section 1 Mendel’s LegacyChapter 9Three Steps of Mendel’s ExperimentsPg 175 Figure 9-3
7Mendel’s Results and Conclusions Section 1 Mendel’s LegacyChapter 9Mendel’s Results and ConclusionsRecessive and Dominant TraitsMendel concluded that inherited characteristics are controlled by factors that occur in pairs.In his experiments on pea plants, one factor in a pair masked the other. The trait that masked the other was called the dominant trait. The trait that was masked was called the recessive trait.
8Mendel’s Results and Conclusions, continued Section 1 Mendel’s LegacyChapter 9Mendel’s Results and Conclusions, continuedThe Law of SegregationThe law of segregation states that a pair of factors is segregated, or separated, during the formation of gametes.Law of segregation is used to describe how traits can disappear and reappear in a certain pattern from generation to generation
9Mendel’s Results and Conclusions, continued Section 1 Mendel’s LegacyChapter 9Mendel’s Results and Conclusions, continuedThe Law of Independent AssortmentThe law of independent assortment states that factors for individual characteristics are distributed to gametes independently of one another.The law of independent assortment is observed only for genes that are located on separate chromosomes or are far apart on the same chromosome.
10Support for Mendel’s Conclusions Section 1 Mendel’s LegacyChapter 9Support for Mendel’s ConclusionsWe now know that the factors that Mendel studied are alleles, or alternative forms of a gene.One allele for each trait is passed from each parent to the offspring.We can see this by looking at ourselves in comparison to our parents, we may have some of both our mother and fatherWe will study this further with Punnett Squares in 9-2
12Chapter 9 Objectives Section 2 Genetic Crosses Differentiate between the genotype and the phenotype of an organism.Explain how probability is used to predict the results of genetic crosses.Use a Punnett square to predict the results of monohybrid and dihybrid genetic crosses.Explain how a testcross is used to show the genotype of an individual whose phenotype expresses the dominant trait.Differentiate a monohybrid cross from a dihybrid cross.
13Genotype and Phenotype Section 2 Genetic CrossesChapter 9Genotype and PhenotypeThe genotype is the genetic makeup of an organism.EX: RR, rr, Rr,The phenotype is the appearance of an organism.EX: The chicken is red (the allele for red feather color is dominant)Homozygous – when both alleles of a pair are alike“ R R ” or “ r r “Heterozygous – when two alleles in a pair are different“ R r ”
14Probability = number of times an event is expected to happen Section 2 Genetic CrossesChapter 9ProbabilityProbability is the likelihood that a specific event will occur.A probability may be expressed as a decimal, a percentage, or a fraction.Probability of drawing a red marbleProbability = 2 red marbles = 2 = 18 marbles totalProbability = number of times an event is expected to happennumber of times an event could happen
15Predicting Results of Monohybrid Crosses Section 2 Genetic CrossesChapter 9Predicting Results of Monohybrid CrossesA Punnett square can be used to predict the outcome of genetic crosses.A cross in which one characteristic is tracked is a monohybrid cross.Genotypic ratio is the ratio of genotypes that appear in offspringPhenotypic ratio is the ratio of offspring’s phenotypes
16Monohybrid Cross of Heterozygous Plants Section 2 Genetic CrossesChapter 9Monohybrid Cross of Heterozygous Plants
17Chapter 9 Y = Yellow y = Green (non-yellow) Section 2 Genetic CrossesChapter 9Y = Yellowy = Green (non-yellow)What is the genotypic ratio for this monohybrid cross?What is the phenotypic ratio for this monohybrid cross?
18Chapter 9 Y = Yellow y = Green (non-yellow) Section 2 Genetic CrossesChapter 9Y = Yellowy = Green (non-yellow)What is the genotypic ratio for this monohybrid cross?1:2:1What is the phenotypic ratio for this monohybrid cross?3 yellow : 1 green 3:1
19Chapter 9 Predicting Results of Monohybrid Crosses, continued Section 2 Genetic CrossesChapter 9Predicting Results of Monohybrid Crosses, continuedA testcross, in which an individual of unknown genotype is crossed with a homozygous recessive individual, can be used to determine the genotype of an individual whose phenotype expresses the dominant trait.R ? x rr
20Chapter 9 Predicting Results of Monohybrid Crosses, continued Section 2 Genetic CrossesChapter 9Predicting Results of Monohybrid Crosses, continuedComplete dominance occurs when heterozygous individuals and dominant homozygous individuals are indistinguishable in phenotype.Ex. Both pea plants PP and Pp for flower color have purple flowersPP or Pp
21Section 2 Genetic Crosses Chapter 9Predicting Results of Monohybrid Crosses, continuedIncomplete dominance occurs when two or more alleles influence the phenotype and results in a phenotype intermediate between the dominant trait and the recessive trait.In four o’clock flowers, red flowers (R) self-pollinate and only produce red offspring, while white flowers (R’) self-pollinate and only produce white offspringIF, red (R) and white (R’) are crossed they will produce 100% pink (RR’) offspringRRR’R’RR’
22Chapter 9 Predicting Results of Monohybrid Crosses, continued Section 2 Genetic CrossesChapter 9Predicting Results of Monohybrid Crosses, continuedCodominance occurs when both alleles for a gene are expressed in a heterozygous offspring.Four human ABO blood types, A, B, and AB and O, are determined by three alleles. The letters A and B refer to two molecules on the surface of the red blood cell. The genotype of a person with blood type AB is IAIB, and neither allele is dominant over the other type. Type AB blood cells carry both A- and B-types of molecules on their surface.
23Predicting Results of Dihybrid Crosses Section 2 Genetic CrossesChapter 9Predicting Results of Dihybrid CrossesA cross in which two characteristics are tracked is a dihybrid cross.To create this type of cross we will use the FOIL method to be used in a 4x4 Punnett Square