Introduction to Genetics with Gregor Mendel: Understanding Inheritance Patterns

1. CHAPTER 11 INTRODUCTION TO GENETICS

2. CHAPTER MYSTERY – video on phsuccessnet.com

3. SECTION 11-1 The Work of Gregor Mendel

4. Key Concept Questions • What is the principle of dominance? • What happens during segregation?

5. Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas • Traits are distinguishing characteristics that are inherited. • Genetics is the study of biological inheritance patterns and variation. • Heredity is the study of inheritance of characteristics from one generation to the next • Gregor Mendel showed that traits are inherited as discrete units. • Many in Mendel’s day thought traits were blended.

6. Mendel made three key decisions in his experiments. • use of purebred plants • control over breeding • observation of seven“either-or” traits

7. The peas were TRUE-BREEDING or purebred • If they were allowed to self-pollinate, they would produce offspring identical to themselves • all purple flowers • all tall • all short • all green seeds • all yellow seeds

8. Quick plant reproduction

9. Fertilization - process in sexual reproduction in which male and female reproductive cells join to form a new cell • Self-pollination – pollen fertilizes egg cells in the same flower • Cross-pollination – pollen from one flower fertilizes egg cells of a different flower = seeds with two parents

10. Original pair of pea plants = P generation = parental generation • Offspring = F1 = first filial generation • Mini Latin Lesson: • Filius = son

11. Mendel controlled the fertilization of his pea plants by removing the male parts, or stamens. He then fertilized the female part, or pistil, with pollen from a different pea plant. • Mendel used pollen to fertilize selected pea plants. • He crossed purebred purple flowers to purebred white flowers • P generation crossed to produce F1 generation • The F1 generation are hybrids – offspring of parents with different characteristics. • interrupted the self-pollination process by removing male flower parts

12. Mendel allowed the resulting plants to self-pollinate. • Among the F1 generation, all plants had purple flowers • Among the F2 generation, some plants had purple flowers and some had white

13. McDougall Littell video – Mendel’s experiment

14. Mendel wondered why the recessive alleles seem to disappear in the F1 generation and then reappear in the F2 generation? • He thought that at some point the alleles for purple and white in the F1 plants were SEGREGATED – separated from each other during the formation of GAMETES – sex cells

15. Mendel observed the same patterns in the first and second generations of his 7 crosses.

16. purple white • Mendel drew three important conclusions. • Traits are inherited as discrete units. • Organisms inherit two copies of each gene, one from each parent. • The two copies segregateduring gamete formation. • The last two conclusions arecalled the law of segregation.

17. The same gene can have many versions. • A gene is a piece of DNA that directs a cell to make a certain protein. • Each gene has a locus, aspecific position on a pair ofhomologous chromosomes. • An allele is any alternative form of a gene occurring at a specific locus on a chromosome.

18. CHAPTER MYSTERY • CLUE #1 – • Parakeets come in four colors: white, green, blue, and yellow. • How many alleles might there be for feather color? • Two alleles because there are four possible phenotypes

19. Principle of Dominance • Alleles can be represented using letters. • A dominant allele is expressed when at least one allele is dominant. • A recessive allele is expressed only when two copies are present. • Dominant alleles are represented by uppercase letters; recessive alleles by lowercase letters.

20. P P P p p PP Pp pp p • Law of segregation • when gametes are produced during meiosis, homologouschromosomes separate from each other • each allele for a trait is packaged into a separate gamete

21. McDougall Littell video – Mendel’s law of Segregation

22. Fun Fact! • Basenjis are small dogs with pointed ears, short silky hair, and rows of wrinkles on their foreheads. • Basenjis cannot bark, but they can make yodeling type sounds. • Basenjis can mate with barking breeds to produce puppies that bark. http://www.youtube.com/watch?v=IFdIWpsJ1cA&feature=related • Hypothesize a genetic explanation for why basenjis cannot bark. • The ability to bark is a dominant trait in dogs. Basenjis have two recessive genes for this character.

23. Key Concept Questions • What is the principle of dominance? • The dominant allele gets expressed and the recessive allele is masked • What happens during segregation? • each allele for a trait is packaged into a separate gamete

24. SECTION 11-2 Genetics and Probability

25. Key Concept Questions • How do geneticists use the principles of probability? • How do geneticists use Punnett squares?

26. Heredity patterns can be calculated with probability. • Probability is the likelihood that something will happen. • Probability predicts an average number of occurrences, not an exact number of occurrences. • Probability applies to random events such as meiosis and fertilization.

27. Probability = number of ways a specific event can occur number of total possible outcomes

28. What is the probability of flipping a coin and landing on heads three times in a row? • ½ x ½ x ½ = 1/8

29. What is the probability of rolling a die and landing on 3 three times in a row? • 1/6 x 1/6 x 1/6 = 1/216

30. Punnett squares illustrate genetic crosses. • The Punnett Square is a grid system for predicting all possible genotypes resulting from a cross. • The axes represent the possible gametesof each parent. • The boxes show the possible genotypes of the offspring. • The Punnett square yields the ratio of possible genotypes and phenotypes.

31. Genes influence the development of traits. • All of an organism’s genetic material is called the genome. • A genotype refers to the makeup of a specific set of genes. • A phenotype is the physical expression of a trait. • Purple is the phenotype • PP and Pp are the genotypes for purple flower color

32. Each parent donates one allele for every gene. • Homozygous describes two alleles that are the same at a specific locus. • PP or pp • Heterozygous describes two alleles that are different at a specific locus. • Pp

33. Both homozygous dominant and heterozygous genotypes express dominant phenotypes. (PP, Pp)

34. homozygous dominant X homozygous recessive • all heterozygous, all dominant phenotype

35. Heterozygous X heterozygous • 1:2:1 homozygous dominant genotype • 3:1 purple:white phenotype • 2 organisms can have the same phenotype but have different genotypes • FF and Ff show the same color but have different alleles

36. Heterozygous X homozygous recessive • 1:1 heterozygous:homozygous recessive • 1:1 purple:white

37. Key Concept Questions • How do geneticists use the principles of probability? • They use probability to try to determine the genetic outcome of a cross between two organisms • How do geneticists use Punnett squares? • They use Punnett squares to determine all the possible outcomes of a particular cross

38. SECTION 11-3 Exploring Mendelian Genetics

39. Key Concept Questions • What is the principle of independent assortment? • What inheritance patterns exist aside from simple dominance?

40. A dihybrid cross involves two traits. • Mendel’s dihybrid crosses with heterozygous plants yielded a 9:3:3:1 phenotypic ratio.

41. yellow green round wrinkled Mendel’s dihybrid crosses led to his second law, the law of independent assortment. • Law of independentassortment • allele pairs separate into gametes independently • non-homologous chromosomes align independently • classes of gametes produced in equal amounts • YR = Yr = yR = yr • only true for genes on separate chromosomes YyRr Yr Yr yR yR YR YR yr yr 1 : 1 : 1 : 1

42. Most traits occur in a range and do not follow simple dominant-recessive patterns. • INCOMPLETE DOMINANCE • One allele is not completely dominant over another

43. Ex) Four o’clock plants Red flowers = RR; white flowers = WW; pink flowers RW • The heterozygous phenotype is somewhere between the two homozygous phenotypes • What phenotypic ratio would you expect to see if two heterozygous plants with pink flowers were crossed? • 1 red:2 pink:1 white

44. CODOMINANCE • Both alleles contribute to the phenotype of the organism • Ex) Cattle that are roan colored – red hairs and white hairs are both displayed in the coat color • Ex) chickens will have an allele for black feathers and one for white feathers that are codominant and you see a speckled looking chicken

45. MULTIPLE ALLELES • Many genes are said to have more than two alleles • Ex) coat color in rabbits – has four different alleles – the rabbit can only have two of those alleles but in various possible combinations

46. CHAPTER MYSTERY • CLUE #2 • Green feathers don’t actually contain green pigments. Rather, they contain a mixture of blue and yellow pigments. • Could feather color be controlled by more than one gene? • There is probably two genes – one for each color

47. POLYGENICTRAITS • Traits controlled by two or more genes • Ex) range of skin color in humans – four different genes control this trait • What Happens in Albino people? • Gene for skin pigment has dominant allele ‘A’ for skin coloration • Homozygous recessive have aa = albino – person who lacks the pigment melanin that gives human skin its color

48. If two people with normal skin color have a child with albinism, what are the odds that a second child will also have albinism? • Use a Punnett square to show your answer

50. 1 in four probability the next child will be albino