1. 1 Mendel & Heredity The study of genetics

2. 2 A Quick Review Define the term gamete. Summarize the relationship between chromosomes & genes. Differentiate between autosomes and sex chromosomes. Describe how independent assortment during meiosis contributes to genetic variation.

3. 3 Thinking Exercises List (in your notebook) five characteristics that are passed on in families. Name one characteristic that may also be inherited but that is also influenced by behavior or environment

4. 4 More Thinking Exercises List all the different traits that could be inherited in plants Are these traits inherited together or separately?

5. 5 Mendel’s Studies Austrian monk Gregor Johann Mendel was the first to develop rules that accurately predict patterns of heredity Heredity is the passing of characteristics (characters) from parent to offspring The patterns Mendel discovered lay the foundation for the science of genetics Mendel built upon the work of a British farmer – T.A. Knight

6. 6 All in a good “Knight’s” work Knight crossed (bred) garden peas with purple flowers to garden peas with white flowers All of the first generation offspring had purple flowers White flowers reappeared in the second generation offspring Mendel’s work differed from Knight’s because he counted the number of each kind of offspring in each generation & analyzed his data

7. 7 Why Study the pea? Several characteristics (characters) of the garden pea (Pisum sativum) exist in two clearly different forms The male & female reproductive parts of the garden pea are enclosed within the same flower The garden pea is small, grows easily, matures quickly, and produces many offspring Note: characters refer to an inherited characteristic while trait refers to a single form of a character.

8. 8 Characteristics of the Pea studied by Mendel

9. 9 Mini- Project: Ads (lab grade) Design a newspaper ad that would attract someone like Mendel to purchase your garden peas for genetic research The ad should mention all of the benefits of Pisum sativum that make it useful for genetic research The ad should be colorful & creative The ad should contain at least one illustration

10. 10 Mendel’s Methods Mendel’s experiments dealt with monohybrid crosses (crosses that involve one pair of contrasting traits – i.e. crossing a purple flowered plant w/ a white flowered plant) Mendel’s experiments involved three steps or three plant generations

11. 11 Step One Mendel allowed each variety of pea to self-pollinate for many generations This ensured that each variety was true- breeding for a particular character Each offspring would show only one form of the character These true-breeding plants served as the parent (P) generation for Mendel’s experiments

12. 12 Step Two Mendel would cross-pollinate two P generation plants with contrasting traits (i.e. white vs. purple flowers) He called their offspring the first filial or F 1 generation Mendel examined each plant in the F 1 generation & recorded the number of F 1 plants expressing each trait

13. 13 Step Three Mendel allowed the F 1 generation to self- pollinate The offspring were designated the F 2 generation Mendel examined each F 2 plant and recorded the number of F 2 expressing each trait

14. calculating mendels ratio mini-lab Mendel’s results Each plant in the F 1 generation showed only one form of the trait. The contrasting trait disappeared! After allowing the F 1 plants to self- pollinate, the missing trait reappeared in some of the offspring Example: 705 plants had purple flowers & 224 had white flowers (this is a 3:1 ratio) Mendel found this same ratio for each of the seven traits he studied.

15. 15 Section Two: Mendel’s Theory Objectives: - Describe Mendel’s four major hypotheses - Define: homozygous, heterozygous, genotype, & phenotype - Compare Mendel’s two laws of heredity

16. 16 Thinking Questions A gardener noticed that some of the flowers on her plants were white. In previous years, the flowers had all been purple. Write an explanation for this difference. Is it possible for an offspring to have traits different from both their parents?

17. 17 Disproving a Theory Prior to Mendel’s work, people believed that offspring were a blend of the traits of their parents Mendel’s results did not support this theory Mendel showed that each pea had two separate “heritable factors” for each character – one from each parent

18. 18 Mendel’s Hypotheses 1. For each inherited character, an individual has two copies of the gene – one from each parent 2. There are alternative versions of genes. These different versions are called alleles

19. 19 Mendel’s hypotheses 3. When two different alleles occur together, one of them may be completely expressed, while the other may have no observable effect on the organism’s appearance. The expressed form of the character is the dominant trait. The “hidden” form of the character is the recessive trait

20. 20 Mendel’s hypotheses 4. When gametes are formed, the alleles for each gene in an individual separate independently of one another. Thus, gametes carry only one allele for each inherited character. When gametes unite during fertilization, each gamete contributes one allele.

21. 21 Modernizing Mendel Geneticists use letters to represent alleles. Dominant alleles are indicated by writing the first letter of the character as a capital letter. (purple flowers are dominant – P) Recessive alleles are indicated by writing the first letter of the dominant character as a lower case letter (white flowers – p)

22. 22 Homozygous vs. Heterozygous Homozygous individuals have two of the same allele for a particular gene ex. Purple flowers (PP); white flowers (pp) Heterozygous individuals have two different alleles for a particular gene ex. Purple flowers (Pp) In heterozygous individuals, only the dominant allele is expressed – the recessive gene is present but unexpressed

23. 23 Genotype vs. Phenotype Genotype refers to the set of alleles an individual has for a character (PP, Pp, pp) Phenotype refer to the physical appearance of a character (purple flowers or white flowers)

24. 24 Working with genotypes & phenotypes The gene for plant height has two versions: T = tall t = dwarf Identify the two alleles for plant height. Identify the genotype and phenotype of the following sets of alleles: TT Tt tt Is the plant with TT alleles homozygous or heterozygous?

25. intro to dragons25 Laws of Heredity The Law of Segregation: the two alleles for a character segregate (separate) when gametes are formed The Law of Independent Assortment: the alleles of different genes separate independently of one another during gamete formation (This law applies only to genes located on separate chromosomes or that are far apart on the same chromosome)

26. 26 Section Three: Studying Heredity Objectives: - predict the results of monohybrid genetic crosses by using Punnett squares - predict the results of dihybrid genetic crosses by using Punnett squares - apply a test cross to determine the genotype of an organism with a dominant phenotype - predict the results of monohybrid genetic crosses using probabilities - analyze a simple pedigree

27. 27 Punnett Squares A Punnett square is a diagram that predicts the outcome of a genetic cross by considering all possible combinations of gametes in the cross This is a simple Punnett square showing us the predicted outcomes of a monohybrid cross – What are the possible genotypes & phenotypes?

28. 28 Using Punnett Squares in dihybrid crosses In a dihybrid cross you need to consider how the four alleles from either parent can combine to form gametes Write the genotypes of these gametes across the top & left of the square Complete the square

29. 29 Test Crosses If you are looking at a purple flowering pea plant, can you identify the genotype of the plant in regard to flower color? Devise a method that would allow you to determine the genotype. In a test cross an individual whose phenotype is dominant, but whose genotype is unknown, is crossed with a homozygous recessive individual

30. 30 Example of a Test Cross I have a plant with a round seed shape but do not know its genotype (R?). I cross the plant with a plant with wrinkled seeds (rr). If all the offspring have round seeds they must be Rr, therefore the unknown genotype must be RR If some offspring have rounded seeds & some have wrinkled seeds, the unknown genotype must be Rr

31. 31 Probability of Outcomes Probability is the likelihood that a specific event will occur Probabilities are expressed in words, as decimals, as percentages, or as fractions Probability = number of one kind of possible outcome total number of all possible outcomes The probability that a coin will land heads up is ½ or 50% (the total number of possibilities is 2 – heads or tails)

32. 32 Probability of specific alleles in gametes We can use probabilities to predict the likelihood of a specific allele showing up in a gamete. Ex: if a pea plant has two alleles for seed shape (round or wrinkled) the plant can contribute either allele to its gametes There are 2 possible outcomes so the chances that the gamete will carry the round gamete is 1 out of 2 or 50%

33. 33 Probability of the Outcome of a cross Two parents are involved in a genetic cross so both their contributions must be considered when predicting the probability of the outcome of a cross The allele the first parent contributes is independent of the allele contributed by the second parent To find the probability that a combination of two independent events will occur, we multiply the separate probabilities together

34. 34 Examples If I cross two pea plants that are heterozygous for seed shape (Rr), the probability of offspring with RR alleles is ½ x ½ = ¼ the probability of offspring with rr alleles is ½ x ½ = ¼ the combination of Rr can occur in two possible ways so the probability of offspring with the Rr genotype is ¼ + ¼ = ½

35. 35 Inheritance of Traits A pedigree is a family history that shows how a trait is inherited over several generations Pedigrees are useful if you want to find out the chances of passing along specific characters to your offspring (i.e. genetic disorders) Individuals can express the trait or be carriers for the trait if they are heterozygous

36. 36 Sample Pedigree

37. 37 Inheritance cont. Genes can be autosomal or sex-linked Autosomal traits will show up equally in both males & females Sex-linked genes are located on the x or y chromosome Most sex linked genes are located on the x chromosome & are recessive Since men have only one x chromosome, they are more likely to exhibit a sex-linked condition Since women have 2 x chromosomes, they must inherit 2 recessive alleles in order to exhibit the sex-linked condition

38. In sickness & health PBL38 Inheritance cont. If a gene is autosomal dominant, every individual with the condition will have a parent with the condition If the gene is autosomal recessive, an individual with the condition can have 1, 2, or 0 parent exhibit the condition Homozygous dominant or heterozygous individuals will exhibit the dominant allele only homozygous recessive individuals will show the recessive allele

39. 39 Section Four: Complex Patterns of Heredity Objectives: - identify five factors that influence patterns of heredity - describe how mutations can cause genetic disorders - list two genetic disorders, and describe their causes & symptoms - evaluate the benefits of genetic counseling

40. 40 Quick Question Propose a mechanism for the inheritance of a trait such as eye color in humans, which can appear as brown, green, blue, and grey

41. 41 Polygenic inheritance Polygenic inheritance occurs when several genes influence a character The genes involved in polygenic inheritance can be found scattered on a single chromosome or on different chromosomes Examples of characters influenced by polygenic inheritance are: eye color, weight, hair color, and skin color

42. 42 Another quick question Explain the following scenario: A plant breeder crosses a red flowered snapdragon plant with a white flowered snapdragon plant and produces a pink flowered snapdragon. + =

43. 43 Intermediate Characters Incomplete dominance occurs when neither allele is completely dominant over the other The phenotype is intermediate between the two traits Ex: pink snapdragons and wavy haired humans

44. 44 Multiple Alleles Some genes have more than two alleles & are called multiple alleles Even for characters with multiple alleles, an individual can only have two of the possible alleles for that gene Ex: Blood types (A, B, AB, O) are controlled by three alleles

45. 45 Codominance Codominance occurs when two dominant alleles are expressed at the same time Codominance differs from incomplete dominance because both traits are expressed

46. 46 Environmental Influences Phenotypes often depend on conditions in the environment Ex: hydrangea will bloom blue in acidic soil but pink in neutral – basic soil artic fox are white in winter because pigment producing genes can’t function in the cold human height is influenced by nutrition human skin tone is affected by exposure to sun

47. 47 Quick Question Why are most bald people male?

48. 48 Genetic Disorders Mutations are changes in genetic material Mutations are rare due to efficient systems for correcting errors When mutations occur, they are often harmful – and are found on the recessive allele Two heterozygous individuals can therefore produce homozygous individuals with genetic disorders (this is where pedigrees come in handy!)

49. 49 Sickle Cell Anemia Sickle cell anemia is the result of a recessive allele that produces a defective form of hemoglobin The defective hemoglobin causes red-blood cells to bend into a sickle shape These deformed red blood cells are less efficient at transporting oxygen through the body The benefit to sickle cell anemia is that it protects against malaria.

50. 50 How People Get Sickle Cell Anemia

51. 51 Cystic Fibrosis Cystic Fibrosis is the most common, fatal, hereditary, recessive disorder in Caucasians (1:25 chance of carrying the recessive allele) 1:2,500 Caucasian infants born in the USA are homozygous for the cf allele Cystic Fibrosis prevents the movement of chloride into and out of cells resulting in respiratory blockages

52. 52 Hemophilia Hemophilia is a sex-linked trait; it impairs the ability of the blood to clot. Because the defective allele is located on the x chromosome, a male inheriting this recessive allele will exhibit hemophilia Hemophilia is prevalent in the royal families of Europe due to inbreeding

53. 53 Huntington’s Disease Huntington’s disease is caused by a dominant allele located on an autosome. Symptoms first appear in individuals in their 30’s & 40’s so the disorder is often unknowingly passed along from one generation to the next Symptoms include loss of muscle control, spasms, mental illness & eventually death Many people accused of witchcraft in the 1600’s were actually suffering from Huntington’s Disease

54. 54 Treating Genetic Disorders Most genetic disorders cannot be cured Because of this many people with family histories of disorders undergo genetic counseling before having children Some genetic disorders can be treated if diagnosed early enough Ex: PKU – individuals lack an enzyme that converts phenylalanine to tyrosine causing a build up of phenylalanine which causes mental retardation – low phenylalanine diets prevent this outcome

55. 55 PKU Dietary Restrictions

56. 56 Gene Therapy Gene therapy is a promising field of study in which defective genes are replaced with healthy genes In 1989 the defective gene for cf was isolated & in 1990 a working copy of the cf gene was transferred to human lung tissue grown in a culture – the cf gene was attached to a cold virus for entry into the lung tissue Similar attempts in humans have failed since we have build up some immunity to cold viruses – new viruses are being investigated with some success