Mendel and Heredity

1. Mendel and Heredity

2. Section 1- The Origin of Genetics • Heredity- The passing of traits from parents to offspring. Example of traits: eye color, eye shape, hair texture, height

3. Gregor Mendel- “Father of Genetics” Where was he from? What was his profession? What organism did he breed different varieties of? He was first to do what? Austria Monk Garden Pea Develop rules that accurately predict patterns of heredity

4. What branch of biology focuses on heredity? Genetics

5. Why were pea plants so good for studying heredity? 1. Traits of the plant were in 2 distinct forms. e.g. flower color was either purple or white 2. The male and female parts are enclosed in the same flower.

6. Why were pea plants so good for studying heredity? 3. Garden peas are small and have a fast growth rate and reproductive cycle.

7. What are the 7 traits that Mendel studied in pea plants? . 1. Flower color 2. Seed color 3. Seed shape 4. Pod color • Pod shape • 6. Flower position • 7. Plant height

8. Traits expressed as Simple Ratios Monohybrid cross (mono= one)- a cross that involves one pair of contrasting traits e.g. Crossing purple flower plant with a white flower plant

9. 3 steps of Mendel’s experiments 1. He made sure that the plants he was going to use were true-breeding. These original parent plants were known as the P generation. 2. He cross-pollinated plants that had contrasting traits. He called the offspring of the cross the F1 generation. He then examined each F1plant and recorded the number of F1 plants expressing each trait.

10. 3 steps of Mendel’s experiments 3. He allowed the F1 generation to self-pollinate and called the offspring of the F1 the F2 generation. He then again counted and characterized each plant.

12. 3 steps of Mendel’s experiments A ratio is a comparison of 2 numbers and can be written as a fraction or with a colon. In F2 generation, 705 purple to 224 white forms a ratio of 3:1. (3 purple: 1 white)

13. *****TAKS Prep Question***** When 2 true-breeding pea plants that show contrasting forms of a trait are crossed, all of the offspring show A. Both forms of the trait B. One form of the trait C. One-fourth of each trait D. A different trait

14. Section II Mendel’s Theory Before Mendel, many people believed in the blending hypothesis in which offspring were a blend of their parents. Mendel’s results did not support the blending hypothesis.

15. Mendel’s Hypothesis 1. For each inherited trait, an individual has 2 copies of the gene- one from each parent. 2. There are alternative versions of genes. Alleles are different versions of a gene.

16. Mendel’s Hypothesis 3. When 2 different alleles occur together, one of them may be completely expressed, while the other may have no observable effect on the organism’s appearance.

17. Mendel’s Hypothesis • Dominant- expressed form of a trait • Dominant alleles are written as capital letters • Recessive- trait that was not expressed • Recessive alleles are written as lower-case letters.

18. Mendel’s Hypothesis 4. When gametes are formed, the alleles in each gene in an individual separate independently of one another. Thus, gametes only carry 1 allele for each inherited trait. When gametes join during fertilization, each gamete contributes 1 allele.

19. Mendel in Modern Times Homozygous- 2 alleles for a trait are the same. Example: PP or pp; YY or yy Heterozygous- 2 alleles for a trait are different. Example: Pp; Yy

20. Mendel in Modern Times The allele for yellow pea seeds is dominant. So, Y = yellow and y = green What color seeds would YY have? Homozygous or Heterozygous? What color seeds would Yy have? Homozygous or Heterozygous? What color seeds would yy have? Homozygous or Heterozygous? yellow yellow green

21. Mendel in Modern Times The allele for freckles is dominant. So, F = freckles and f = no freckles. Would a child with FF have freckles? Homozygous or Heterozygous? Would a child with Ff have freckles? Homozygous or Heterozygous? Would a child with ff have freckles? Homozygous or Heterozygous? yes yes no

22. *****TAKS Prep Question***** If a pea plant is heterozygous for a particular trait, how can the alleles that control the trait be characterized? A. Two recessive B. Two dominant C. One dominant, one recessive D. Three dominant, one recessive

23. Mendel in Modern Times Genotype- the set of alleles that an individual has Phenotype- the physical appearance of a trait GenotypePhenotype F= freckles FF freckles f= no freckles Ff freckles ff no freckles

24. Mendel in Modern Times GenotypePhenotype P = purple flower pp p = white flower Pp PP white purple purple

25. Mendel in Modern Times GenotypePhenotype Y= yellow seed y = green seed YY yellow Yy yellow green yy

26. The Laws of Heredity The Law of Segregation-2 alleles for a trait segregate when gametes are formed.

27. The Laws of Heredity The Law of Independent Assortment-the alleles of different genes separate independently of one another during gamete formation. Example: Gene for height separate differently from flower color or seed shape

28. The Laws of Heredity • Mendel found the inheritance of one trait did not influence the inheritance of another trait. For example: plant height did not influence the inheritance of another trait such as flower color

29. The Laws of Heredity • To study how different pairs of genes are inherited Mendel conducted dihybrid crosses. A dihybrid cross is a cross that considers 2 pairs of contrasting traits. For example: a cross that considers both plant height and flower color.

30. The Laws of Heredity Example: PPYY x ppyy purple white flowers flowers & & yellow green seeds seeds

31. Section III Studying Heredity Punnett squares-a diagram that predicts the outcome of a genetic cross by considering all combinations of gametes in a cross Punnett squares allow direct and simple predictions. Punnett squares show probability, NOT actual results.

32. Section III Studying Heredity Probability- the likelihood that specific events will occur. It can be represented as a ratio or a fraction or a percentage. ***Practice using the examples in your notes

33. Dihybrid Cross • Predictions for 2 triats: • You can predict 2 traits by making a dihybrid cross. Use the FOIL method for setting up the dihybrid cross. • F – First • O – outside • I – inside • L – last • Practice on the two examples.

34. Inheritance of Traits Geneticists often prepare a pedigree which is a family history that shows how a trait is inherited. Pedigrees are particularly helpful if the trait is a geneticdisorder and the family members want to know if they are carriers. Carriers- individuals who are heterozygous for an inherited disorder but do not show symptoms

36. Inheritance of Traits Albinism Pedigree What do the squares represent? What do the circles represent? What does it mean if the shape is shaded in? males females Affected individual

37. Albinism- the body is unable to produce an enzyme necessary for the production of melanin Albinism is a genetic disorder transmitted by a recessive allele.

38. Examine Pedigree I, which traces the dimples trait through three generations of a family. Blackened symbols represent people with dimples. Circles represent females, and squares represent males. Although Jane and Joe Smith have dimples, their daughter, Clarissa, does not. Joe’s father has dimples, but his mother, and his sister, grace, do not. Jane’s father, Mr. Renaldo, her brother, Jorge, and her sister, Emily, do not have dimples, but her mother does.

39. Inheritance of Traits Sex-linked trait- a trait whose allele is located on the X chromosome Most sex-linked traits are recessive and are usually only seen in males.

40. *****TAKS Prep Question***** A cross between two pea plants that produce yellow seeds results in 124 offspring: 93 produce yellow seeds and 31 produce green seeds. What are the likely genotypes of the plants that were crossed? A. Both Yy C. Both yy D. One YY, one Yy B. Both YY

41. Traits Influenced by Several Genes Polygenic trait- when several genes influence one trait The genes for a polygenic trait may be scattered along the same chromosome or located on different chromosomes. Because of independent assortment and crossing-over, many different combinations appear in the offspring. Example: eye color, skin color, height, weight, hair color

42. Intermediate Traits Incomplete dominance- when an individual displays an intermediate trait Example: 1. cross red snapdragons with white snapdragons and make pink ones 2. cross straight haired parent with curly haired parent = child with wavy hair

43. Sample Problem RR = red snapdragon flower RW = pink snapdragon flower WW = white snapdragon flower Parent # 1 is Pink x Parent #2 is white RW x WW Make a Punnet Square!!!!!!! _____% red ____% white ____% pink 50 0 50

44. Sample Problem BB = black hair; BW = grey hair; WW = white hair Parent # 1 black hair BB x WW Parent # 2 white hair Offspring: ___% black ___ % grey ___ % white Make a Punnet Square!!!! 0 100 0

45. Traits Controlled by Genes with Three or More Alleles Multiple Alleles- genes with 3 or more alleles Example: ABO blood types are determined by 3 alleles 4 different blood types are: A, B, AB, and O

46. Traits Controlled by Genes with Three or More Alleles IA = A; IB = B; i = O Fill in the following blood types with the given genotypes: IA IA = ______ IAi = ______ IB IB = ______ IBi = ______ IA IB = ______ ii = ______ A A B B AB O

47. Traits with 2 Forms Displayed at the Same Time Codominance- both forms of the trait are displayed (2 different dominant alleles are shown) *** This is different from incomplete dominance because both traits are displayed. Example: ABO blood types- Type AB blood cells carry both A and B types

48. Traits influenced by the Environment Hydrangea flowers What color are hydrangeas that grow in acidic soil? ___________ What color are hydrangeas that grow in neutral to basic soils? ___________ blue pink

49. Traits influenced by the Environment The color of the Arctic Fox is determined by temperature. What color is the fox in summer? ____________ What causes the fox’s cat to darken? _________ What color does the fox turn in the winter?____ What advantage is this to the fox?____________ reddish brown Enzymes that make pigments white camouflage

50. Genetic Disorders In order for a person to develop and function normally, the proteins encoded by his or her genes must function precisely. Sometimes genes get damaged or are copied incorrectly, resulting in faulty proteins. Changes in genetic material are called mutations.