1 / 23

Chapter 9

Chapter 9. Genetics. Section 1 Mendel’s Legacy: Objectives. Describe how Mendel was able to control how his pea plants were pollinated Describe the steps in Mendel’s experiment on true-breeding garden peas Distinguish between dominant and recessive traits

ulmer
Download Presentation

Chapter 9

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 9 Genetics

  2. Section 1 Mendel’s Legacy: Objectives • Describe how Mendel was able to control how his pea plants were pollinated • Describe the steps in Mendel’s experiment 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

  3. Gregor Mendel • The study of how characteristics are transmitted from parents to offspring is called genetics • Mendel is considered the “father” of genetics because of his work with heredity • Heredity is the passing of traits from parents to their offspring

  4. Mendel’s Garden Peas • Mendel observed characteristics of pea plants • Traits are genetically determined variants of a characteristic • For Mendel, each characteristic occurred in two contrasting traits

  5. Mendel’s Methods • Self-pollination occurs when pollen is transferred from the anthers (male) of a plant to the stigma (female) of the same plant • Cross-pollination occurs when pollen is transferred between flowers of two different plants • Mendel controlled his experiments by manually pollinating the other plants through cross-pollination. He removed anthers from the plants he was working with.

  6. Mendel’s Experiments P • Mendel bred plants for several generations that were true-breeding (self-pollinating) for specific traits and called these the P generation(“parental”) F1 F2 • True breeding pea plants always produce offspring which can only have one form of a trait • EX: true-bred pea plants with yellow pods will self-pollinate and produce offspring with yellow pods • P generation offspring are called the F1 generation. F1 generation offspring are the F2 generation

  7. Three Steps of Mendel’s Experiments 100 Greatest Discoveries Shorts: Genetics

  8. Mendel’s Results and Conclusions 1. Recessive and Dominant Traits • Mendel 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.

  9. Mendel’s Results and Conclusions 2. The Law of Segregation • The law of segregation states that a pair of factors is segregated, or separated, during the formation of gametes • The law of segregation is used to describe how traits can disappear and reappear in a certain pattern from generation to generation

  10. Mendel’s Results and Conclusions 3. The Law of Independent Assortment • The law of independent assortment states that factors for individual characteristics are distributed to gametes independent 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

  11. Support for Mendel’s Conclusions • We 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 comparing ourselves to our parents – we have some of both our mother and father • We can study this further with Punnett Squares

  12. HomeWork Section 9.1 Review Pp 178 #1-8

  13. Section 2 Genetic Crosses: Objectives • 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

  14. Genotype and Phenotype • The genotype is the genetic makeup of an organism • The phenotype is the appearance of an organism • EX: The chicken is red (the allele for red feather color is dominant) • An organism is homozygous when both alleles of a pair are alike • “ R R ” or “ r r “ • An organism is heterozygous when two alleles in a pair are different • “ R r ”

  15. Probability • Probability is the likelihood that a specific event will happen • A probability may be expressed as a decimal, a percentage, or a fraction Probability = number of times an event is expected to happen number of times an event could happen Probability of drawing a red marble? Probability = 2 red marbles = 2 = 1 8 marbles total 8 4

  16. Predicting Results of Monohybrid Crosses • A Punnett square can be used to predict the outcome of genetic crosses • A cross in which one characteristic is tracked is a monohybrid cross • The genotypic ratio is the ratio of genotypes that appear in offspring • The phenotypic ratio is the ratio of offspring’s phenotypes

  17. Monohybrid Cross of Heterozygotes Y = yellow y = green (non-yellow) What is the genotypic ratio for this monohybrid cross? 1 YY: 2 Yy : 1 yy 1:2:1 What is the phenotypic ratio for this monohybrid cross? 3 yellow: 1 green 3:1

  18. Predicting Results of Monohybrid Crosses • A testcross is when an individual of unknown genotype is crossed with a homozygous recessive individual to determine the genotype of the individual whose phenotype expresses the dominant trait • EX: rrtestcrossed with ?? r r ? ? Rr Rr What is the genotype of the unknown individual? Rr rr rr

  19. Predicting Results of Monohybrid Crosses • Complete dominance occurs when heterozygous individuals and dominant homozygotes individuals are indistinguishable in phenotype • EX: Pea plants PP and Pp for flower color both have purple flowers PP x Pp

  20. Predicting Results of Monohybrid Crosses • Incomplete dominance occurs when two or more alleles influence the phenotype and result in a intermediate phenotype between the dominant trait and the recessive trait • EX: In four o’clock flowers, red flowers (R) produce only red offspring and white flowers (R’), only white offspring (both via self-pollination) • If red (R) and white (R’) are crossed, the produce 100% pink (RR’) offspring

  21. Predicting Results of Monohybrid Crosses • Codominance occurs when both alleles for a gene are expressed in heterozygous offspring • The human blood types (A, B, AB, and O) are determined by three alleles. • A and B refer to two molecules on the surface of the red blood cell • The genotype of someone with AB blood is IAIB and neither allele is dominant over the other • AB blood cells carry both A and B molecules on their surface

  22. Predicting Results of Dihybrid Crosses • A cross in which two characteristics are tracked is a dihybrid cross • To create this type of cross we use the FOIL method to be used in a 4x4Punnett square

  23. Homework Section 9.2 Review Pp 186 #1-7

More Related