Mendelian Genetics

1. Mendelian Genetics

2. 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.

3. Every living thing has a set of characteristics inherited from its parent or parents. The delivery of characteristics from parent to offspring is called heredity.

4. The scientific study of heredity, known as genetics, is the key to understanding what makes each organism unique.

5. Gregor Mendel “Father of Genetics” Studied heredity carefully & objectively using pea plants

6. The founder of the modern science of genetics …. Mendel was in charge of the monastery garden, where he was able to do the work that changed biology forever.

7. Mendel carried out his work with ordinary garden peas, partly because peas are small and easy to grow. A single pea plant can produce hundreds of offspring. Today we call his work with peas a “model system.”

8. Scientists use model systems because they are convenient to study and may tell us how other organisms, including humans, actually function.

9. By using peas, Mendel was able to carry out, in just one or two growing seasons, experiments that would have been impossible to do with humans and that would have taken decades—if not centuries—to do with other large animals.

10. What did Mendel know? Mendel knew that the male part of each flower makes pollen, which contains sperm—the plant’s male reproductive cells. Similarly, Mendel knew that the female portion of each flower produces reproductive cells called eggs.

11. During sexual reproduction, male and female reproductive cells join in a process known as fertilizationto produce a new cell. In peas, this new cell develops into a tiny embryo encased within a seed

12. Pea Plants can reproduce through: 1. Self-pollination 2. Cross-pollination

13. Self-Pollination Pollenfrom a flower fertilizes an egg cell on the same flower-common in pea plants A plant grown from a seed produced by self-pollination inherits all of its characteristics from the single plant that bore it. In effect, it has a single parent.

14. Mendel’s garden had several stocks of pea plants that were “true breeding” and would produce offspring with identical traits as themselves. They were self pollinating.

15. True-Breeding Stock Always passes its characteristics to the next generation Ex. True-breeding stock of pea plants always produces tall plants with green pods

16. Mendel decided to “cross” his stocks of these plants—he caused one plant to reproduce with another plant.

17. Cross-Pollination Pollen from one plant fertilizes eggs from another plant Offspring have 2 different parents a.k.a. cross

18. He had to prevent self-pollination, so he cut away the male parts of a flower and then dusted pollen from a different plant onto the female part of that flower.

19. Cross-pollination allowed Mendel to breed plants with different features from those of their parents and then study the results.

20. Trait A specific characteristic of an individual and may vary from one individual to another; a characteristic that distinguishes one individual from another

21. Hybrid When two plants cross or cross pollinate, the offspring is called a hybrid HybridOffspring of parents with different characteristics Ex. Tall plant X short plant

22. Mendel Studied 7 Traits • Seed shape • Seed color • Seed coat color • Pod shape • Pod color • Flower position • Plant height

23. PGeneration True breeding generation “Parents”

24. Mendel crossed plants with each of the seven contrasting characteristics and then studied their offspring.

25. F1 Generation The hybrids F stands for filiusmeaning son in Latin

27. For each trait studied in Mendel’s • experiments, all the offspring had • the characteristics of only one of their • parents, as shown in the table.

28. In each cross, the nature of the other parent, with regard to each trait, seemed to have disappeared. Ex> tall x short did not produce medium sized plants, they were all tall

29. Mendel allowed self pollination of the F1 generation among themselves to occur…..

30. F2Generation Result of a cross between two F1 hybrids

32. Genes The name given to different traits of an organism; it is the unit that determines traits Ex. If a plant is tall, it has a gene for tallness.

33. Mendel concluded that each pea plant must contain two traits—one from each parent

34. Each of the traits Mendel studied was controlled by a gene that occurred in two contrasting varieties, one observable and one “masked”. These gene variations produced different expressions, or forms, of each trait.

35. Alleles Different forms of a gene for a specific trait

36. Ex. The gene that determines height in pea plants has 2 alleles; one that produces a tall plant & one that produces a short plant

37. Some genes have only 2 alleles while others have dozens of different alleles Alleles are represented by either uppercase or lowercase letters

38. Two Types of Alleles 1. Dominant Allele 2. Recessive Allele

39. Dominant Allele Allele that will be expressed when present

40. Ex. If a plant has one allele for tallness & one for shortness, then the plant will be tall because the dominant allele is the allele for tallness that will be expressed by the plant

41. Expressed by Uppercase Letters Ex. Dominant allele for tallness: “T”

42. Recessive Allele Allele that will not be expressed * An organism with a recessive allele for a trait will exhibit that form only when the dominant allele for that trait is not present. Represented by lowercase letters

43. If a plant has a tallness allele & an allele for shortness, the plant will be tall dominant, making the shortness allele recessive. The plant would be tall, not short.

44. The only way a recessive short plant would be produced was if no dominant allele for tall was present

45. Example: Recessive Allele for tallness “t”

46. In Mendel’s experiments, the allele for tall plants was dominant and the allele for short plants was recessive.

47. Likewise, the allele for yellow seeds was dominant over the recessive allele for green seeds.

48. Mendel questioned how different forms of a gene are distributed to offspring.

49. Mendel questioned what had happened to the recessive alleles. By allowing all seven kinds of F1 hybrids to self-pollinate, he would get his answer. self-pollinating

50. From the F1 X F1 crosses, Mendel discovered several rules concerning how traits were transferred from generation to generation