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Intro to Genetics

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  1. Intro to Genetics Chapter 11.1-11.3 p. 306-322 Chapter 11 and 14 Genetics 2010

  2. Key terms • Genetics • Fertilization • Trait • Hybrid • Gene • Allele • Principle of dominance • Segregation • Gamete • Probability • Homozygous • Heterozygous • Phenotype • Genotype • Punnett square • Independent assortment • Incomplete dominance • Codominance • Multiple allele • Polygenic trait Chapter 11 and 14 Genetics 2010

  3. Review? Heredity: What is a gene? is a segment of DNA that is located in a chromosome and that codes for a specific trait Crossing over: How does it contribute to the physical differences between siblings? exchange of genetic material between homologous chromosomes genetic recombination Chapter 11 and 14 Genetics 2010

  4. THINK ABOUT IT What is an inheritance? It is something we each receive from our parents—a contribution that determines our blood type, the color of our hair, and so much more. What kind of inheritance makes a person’s face round or hair curly Where does an organism get its unique characteristics An individual’s characteristics are determined by factors that are passed from one parental generation to the next. The delivery of characteristics from parent to offspring is called heredity.  The scientific study of heredity, known as genetics, is the key to understanding what makes each organism unique Chapter 11 and 14 Genetics 2010

  5. leucism • This alligator is one of 18 white alligators discovered southwest of New Orleans in 1987 by a fisherman. • How is he different from alligators you have seen? • It is not a different species and it is not albino. • Albinos have off-white or yellowish skin and colorless irises or look pink • This alligator is more rare than one that would be an albino. Chapter 11 and 14 Genetics 2010

  6. Need to know!! • Describe how Mendel was able to control 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 Chapter 11 and 14 Genetics 2010

  7. Mendel’s Legacy • Genetics is the field of biology devoted to understanding how characteristics or traits are transmitted from parents to offspring. Genetics was founded with the work of Gregor Johann Mendel. Chapter 11 and 14 Genetics 2010

  8. Gregor Mendel1822-1884 • Studied science and mathematics (statistics) • Studied heredity (characteristics from parents to offspring) • Studied garden peas, characteristics, flower color, height, pod appearance, texture or traits • A trait is a specific characteristic of an individual, such as seed color or plant height, and may vary from one individual to another. • Led to basic principles of genetics • Web demo holt • http://my.hrw.com/index.jsp Chapter 11 and 14 Genetics 2010

  9. Mendel’s Methods • Controlled how plants were pollinated • Or how the pollen grains produced in the male reproductive parts of a flower (anthers/stamen) to the female reproductive parts of the flower (stigma/pistle) Two types: • Self- pollination • Cross pollination Chapter 11 and 14 Genetics 2010

  10. Chapter 11 and 14 Genetics 2010

  11. Mendel’s Methods cont: • Self- pollination- occurs when pollen is transferred from the anthers of a flower to the stigma of either that flower or another flower on the same plant. *Can be prevented if remove male parts 2. Cross-pollination- occurs between flowers of two plants, can be specific for traits *Mendel used this method to study plants Web demo holt Chapter 11 and 14 Genetics 2010

  12. Mendel’s Experiments • True-breeding or pure for a trait will produce offspring with a trait of self-pollinate Ex: yellow pod x yellow pod = yellow pod • Cross pollinated pairs of plants that were true-breeding for one trait and then another • True-breeding parents were P generation • First generations F1 • Second generations F2 • Mendel’s crosses Web demo holt Chapter 11 and 14 Genetics 2010

  13. Chapter 11 and 14 Genetics 2010

  14. Genes and Alleles From these results, Mendel drew two conclusions. His first conclusion formed the basis of our current understanding of inheritance. An individual’s characteristics are determined by factors that are passed from one parental generation to the next. Scientists call the factors that are passed from parent to offspring genes. Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting varieties. These gene variations produced different expressions, or forms, of each trait. The different forms of a gene are called alleles Chapter 11 and 14 Genetics 2010

  15. Dominant and Recessive Traits Mendel’s second conclusion is called the principle of dominance. This principle states that some alleles are dominant and others are recessive. An organism with at least one dominant allele for a particular form of a trait will exhibit that form of the trait. An organism with a recessive allele for a particular form of a trait will exhibit that form only when the dominant allele for the trait is not present. Chapter 11 and 14 Genetics 2010

  16. Segregation How are different forms of a gene distributed to offspring? During gamete formation, the alleles for each gene segregate from each other, so that each gamete carries only one allele for each gene. Chapter 11 and 14 Genetics 2010

  17. Results and conclusions • Pair of factors (genes) controlled for traits • Only one trait was visible in F1 generation (dominant factor) • Traits appeared in the F2 generations in 3:1 ratio (recessive factor) • Law of segregation- pair of factors are separated during formation of gametes or meiosis • Law of Independent Assortment- factors separate independently of one another during the formation of gametes (meiosis) Chapter 11 and 14 Genetics 2010

  18. Chapter 11 and 14 Genetics 2010

  19. Chapter 11 and 14 Genetics 2010

  20. Lesson Overview 11.2 Applying Mendel’s Principles Chapter 11 and 14 Genetics 2010

  21. Key questions? • 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 a 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 Chapter 11 and 14 Genetics 2010

  22. Genetic Crosses • Today, geneticists rely on Mendel’s work to predict the likely outcome of genetic crosses. In this section you will learn how to predict the probable genetic makeup and appearance of offspring resulting from specified crosses. Chapter 11 and 14 Genetics 2010

  23. Probability and Punnett Squares How can we use probability to predict traits? Punnett squares use mathematical probability to help predict the genotype and phenotype combinations in genetic crosses. Mendel realized that the principles of probability could be used to explain the results of his genetic crosses. Probability is the likelihood that a particular event will occur. Chapter 11 and 14 Genetics 2010

  24. Probability and Punnett Squares For example, there are two possible outcomes of a coin flip: The coin may land either heads up or tails up. The chance, or probability, of either outcome is equal. Therefore, the probability that a single coin flip will land heads up is 1 chance in 2. This amounts to 1/2, or 50 percent If you flip a coin three times in a row, what is the probability that it will land heads up every time? Each coin flip is an independent event, with a one chance in two probability of landing heads up. Therefore, the probability of flipping three heads in a row is: 1/2 × 1/2 × 1/2 = 1/8 Past outcomes do not affect future ones. Just because you’ve flipped 3 heads in a row does not mean that you’re more likely to have a coin land tails up on the next flip . Chapter 11 and 14 Genetics 2010

  25. Probability • The likelihood that a specific event will occur. • Can be expressed as a: • Decimal • Percentage • Fraction Probability=(# of time event expected to happen)/ (# of time it could happen) Chapter 11 and 14 Genetics 2010

  26. Chapter 11 and 14 Genetics 2010

  27. Using Segregation to Predict Outcomes The way in which alleles segregate during gamete formation is every bit as random as a coin flip. Therefore, the principles of probability can be used to predict the outcomes of genetic crosses. Chapter 11 and 14 Genetics 2010

  28. Terms • Genotype- genetic makeup, alleles that are inherited from parents (PP, Pp, pp) • Phenotype- physical appearance (color, height), does not always resemble genotype due to environment factors • Homozygous- alleles are the same, can be dominant (PP) or recessive (pp) • Heterozygous- alleles are different (Pp) Chapter 11 and 14 Genetics 2010

  29. More terms • Monohybrid cross- cross with only one characteristic, offspring are monohybrids • Punnett square- used to do monohybrid crosses, used to predict outcomes • Genotypic ratio- ratio of genotypes that appear (1BB: 2Bb: 1bb) • Phenotypic ratio- ratio of phenotypes that appear (3 brown : 1 black) • Test cross- unknown organism is crosses with a homozygous recessive Chapter 11 and 14 Genetics 2010

  30. How To Make a Punnett Square for a One-Factor Cross Write the genotypes of the two organisms that will serve as parents in a cross. In this example we will cross a male and female osprey that are heterozygous for large beaks. They each have genotypes of Bb. Bb and Bb Chapter 11 and 14 Genetics 2010

  31. How To Make a Punnett Square Draw a table with enough spaces for each pair of gametes from each parent. Enter the genotypes of the gametes produced by both parents on the top and left sides of the table. Chapter 11 and 14 Genetics 2010

  32. How To Make a Punnett Square Fill in the table by combining the gametes’ genotypes. Chapter 11 and 14 Genetics 2010

  33. How To Make a Punnett Square Determine the genotypes and phenotypes of each offspring. Calculate the percentage of each. In this example, three fourths of the chicks will have large beaks, but only one in two will be heterozygous. Chapter 11 and 14 Genetics 2010

  34. Chapter 11 and 14 Genetics 2010

  35. Types of crosses: • Homozygous x Homozygous (PP x pp) • Homozygous x Heterozygous (PP x Pp) (complete dominance) • Heterozygous x Heterozygous (Pp x Pp) • Test cross (pp x P_) Chapter 11 and 14 Genetics 2010

  36. Types of crosses: • Incomplete dominance- F1 offspring has a phenotype in between that of parents, Cross a white (rr) flower with a Red flower (RR)= pink flower (Rr) Chapter 11 and 14 Genetics 2010

  37. Types of crosses F. Codominance-both alleles fro a gene are expressed on a heterozygous offspring, neither trait is dominant or recessive, blood types Chapter 11 and 14 Genetics 2010

  38. Independent Assortment How do alleles segregate when more than one gene is involved? The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes. Mendel wondered if the segregation of one pair of alleles affects another pair. Mendel performed an experiment that followed two different genes as they passed from one generation to the next. Because it involves two different genes, Mendel’s experiment is known as a two-factor, or dihybrid, cross. Single-gene crosses are monohybrid crosses. Chapter 11 and 14 Genetics 2010

  39. Dihybrid crosses • Two characteristics are tracked, results are dihybrid Types of crosses( 4 x4 box) • Homozygous RRYY x Homozygous rryy • Heterozygous RrYy x Heterozygous RrYy (9:3:3:1) Chapter 11 and 14 Genetics 2010

  40. Chapter 11 and 14 Genetics 2010

  41. A Summary of Mendel’s Principles What did Mendel contribute to our understanding of genetics? Mendel’s principles of heredity, observed through patterns of inheritance, form the basis of modern genetics At the beginning of the 1900s, American geneticist Thomas Hunt Morgan decided to use the common fruit fly as a model organism in his genetics experiments. The fruit fly was an ideal organism for genetics because it could produce plenty of offspring, and it did so quickly in the laboratory. Before long, Morgan and other biologists had tested every one of Mendel’s principles and learned that they applied not just to pea plants but to other organisms as well. The basic principles of Mendelian genetics can be used to study the inheritance of human traits and to calculate the probability of certain traits appearing in the next generation. Chapter 11 and 14 Genetics 2010

  42. Human Heredity Chapter 14 p. 390-410 Chapter 11 and 14 Genetics 2010

  43. A little Q and A • Can you ID some parts to the chromosomes - centromere, chromatids • How many chromosomes are found in the normal human genome 46 (2n) • Each chromosome contains many genes Chapter 11 and 14 Genetics 2010

  44. A little Q and A • Differences between dominant and recessive dominance: when an allele that masks the presence of another allele for the same characteristic Recessive: when an allele that is masked by the presence of another allele for that same characteristic Can you give examples? Chapter 11 and 14 Genetics 2010

  45. Objectives • Distinguish between sex chromosomes and autosomes • Explain the role of sex chromosomes in sex determination • Describe how an X or Y linked gene affects the inheritance of genes in linkage groups • Distinguish between chromosomes mutations and gene mutations Chapter 11 and 14 Genetics 2010

  46. Chromosomes and Inheritance • Francis Collins and his lab group discovered the gene responsible for Cystic Fibrosis. CS is often fatal genetic disorder. Thick, sticky mucus builds up and blocks ducts in the pancreas and intestines and causes difficulty in breathing. • In this chapter we will learn how diseases and characteristics are inherited and expressed. Chapter 11 and 14 Genetics 2010

  47. Chromosomes • 1900s Thomas Hunt Morgan experimented with Drosophila melanogaster • Observed that they had 4pairs of chromosomes • 3 pairs were identical in male and female • The fourth pairs was the sex chromosomes XX female, XY male Chapter 11 and 14 Genetics 2010

  48. Sex chromosomes and autosomes • Sex chromosomes- contain genes that determine the sex (gender) of an individual • Autosomes- non sex chromosomes Sex determination- Sex chromosomes pair during meiosis Child will always receive a x chromosome from the mother SRY gene- sex-determining Region Y, if have this gene hormones are released and testes form and if not ovaries form Chapter 11 and 14 Genetics 2010

  49. Can you determine the probability of the sex of the child? • Cross a Male and a Female XY x XX 2. Set up your punnett square 3. What are your ratios? 4. Who determines the sex of the child? Chapter 11 and 14 Genetics 2010

  50. Sex Chromosomes This Punnett square illustrates why males and females are born in a roughly 50 : 50 ratio. All human egg cells carry a single X chromosome (23,X). However, half of all sperm cells carry an X chromosome (23,X) and half carry a Y chromosome (23,Y). This ensures that just about half the zygotes will be males and half will be females. Chapter 11 and 14 Genetics 2010