10.1 Section Objectives – page 253

1. 10.1 Section Objectives – page 253 Group 1 Group 2 1. What possible combinations can result from combining one coin from each group? 2. What is the ratio of the possible combinations?

2. Section 10.1 Summary – pages 253-262 Why Mendel Succeeded • It was not until the mid-nineteenth century that Gregor Mendel, an Austrian monk, carried out important studies of heredity. • Heredity: the passing on of characteristics from parents to offspring. • Traits: Characteristics that are inherited are called

3. Section 10.1 Summary – pages 253-262 Why Mendel Succeeded • Mendel was the first person to succeed in predicting how traits are transferred from one generation to the next. • A complete explanation requires the careful study of genetics • Genetics: the branch of biology that studies heredity.

4. Section 10.1 Summary – pages 253-262 Mendel chose his subject carefully • Mendel chose to use the garden pea in his experiments for several reasons. • Garden pea plants reproduce sexually, which means that they produce gametes. • Gametes: male and female sex cells

5. Section 10.1 Summary – pages 253-262 Mendel chose his subject carefully • The male gamete forms in the pollen grain, which is produced in the male reproductive organ. • The female gamete forms in the female reproductive organ. • Fertilization: the process in which the male gamete unites with the female gamete. • Zygote: The resulting fertilized cell

6. Section 10.1 Summary – pages 253-262 Mendel chose his subject carefully • Pollination: the transfer of pollen grains from a male reproductive organ to a female reproductive organ in a plant

7. Section 10.1 Summary – pages 253-262 Mendel chose his subject carefully • When he wanted to breed, or cross, one plant with another, Mendel opened the petals of a flower and removed the male organs. Remove male parts

8. Section 10.1 Summary – pages 253-262 Mendel chose his subject carefully • He then dusted the female organ with pollen from the plant he wished to cross it with. Pollen grains Transfer pollen Female part Male parts Cross-pollination

9. Section 10.1 Summary – pages 253-262 Mendel chose his subject carefully • This process is called cross-pollination. • By using this technique, Mendel could be sure of the parents in his cross.

10. Section 10.1 Summary – pages 253-262 Mendel was a careful researcher • He studied only one trait at a time to control variables, and he analyzed his data mathematically. • The tall pea plants he worked with were from populations of plants that had been tall for many generations and had always produced tall offspring.

11. Section 10.1 Summary – pages 253-262 Mendel was a careful researcher • Such plants are said to be true breeding for tallness. • Likewise, the short plants he worked with were true breeding for shortness.

12. Section 13.1 Summary – pages 337 - 340 Selective Breeding • From ancient times, breeders have chosen plants and animals with the most desired traits to serve as parents of the next generation. • Breeders of plants and animals want to be sure that their populations breed consistently so that each member shows the desired trait.

13. Section 13.1 Summary – pages 337 - 340 Selective Breeding • The process of selective breeding requires time, patience, and several generations of offspring before the desired trait becomes common in a population. • Increasing the frequency of desired alleles in a population is the essence of genetic technology.

14. Section 13.1 Summary – pages 337 - 340 Inbreeding develops pure lines • To make sure that breeds consistently exhibit a trait and to eliminate any undesired traits from their breeding lines, breeders often use the method of inbreeding. • Inbreeding: mating between closely related individuals. It results in offspring that are homozygous for most traits.

15. Section 13.1 Summary – pages 337 - 340 Inbreeding develops pure lines • Inbreeding can bring out harmful, recessive traits because there is a greater chance that two closely related individuals both may carry a harmful recessive allele for the trait.

16. Section 13.1 Summary – pages 337 - 340 Inbreeding develops pure lines • Horses and dogs are two examples of animals that breeders have developed as pure breeds.

17. Section 13.1 Summary – pages 337 - 340 Hybrids are usually bigger and better • A hybrid is the offspring of parents that have different forms of a trait. • Hybrids produced by crossing two purebred plants are often larger and stronger than their parents.

18. Section 13.1 Summary – pages 337 - 340 Hybrids are usually bigger and better • Many crop plants such as wheat, corn, and rice, and garden flowers such as roses and dahlias have been developed by hybridization.

19. SELECTIVE BREEDING • The Liger is the result of breeding a female Tiger to a male Lion. • The liger has both stripes and spots. The stripes are inherited from its tiger parent and the spots from the lion parent. • On their hind legs, ligers stand approximately 12 feet tall. At most, ligers may weigh up to 1,000 pounds.

20. The Cama is the result of breeding a Llama to a Camel.Parents in background of picture.

21. The Zebroid is the result ofbreedinga female Horse and a male Zebra. The Zedonk / Zonkey is the result of breeding a female Donkey and male Zebra.

23. The Mule is the result of breeding a female horse(mare) to a male donkey (jack). Themule is superior to the horse in strength,endurance, intelligence and disease resistance.

24. Section 10.1 Summary – pages 253-262 Mendel’s Monohybrid Crosses • Hybrid: the offspring of parents that have different forms of a trait, such as tall and short height. • Mendel’s first experiments are called monohybrid crosses because mono means “one” and the two parent plants differed from each other by a single trait—height.

25. Section 10.1 Summary – pages 253-262 The first generation • Mendel selected a six-foot-tall pea plant that came from a population of pea plants, all of which were over six feet tall. • He cross-pollinated this tall pea plant with pollen from a short pea plant. • All of the hybrid offspring grew to be as tall as the taller parent.

26. Section 10.1 Summary – pages 253-262 The second generation • Mendel allowed the tall plants in this first generation to self-pollinate. • After the seeds formed, he planted them and counted more than 1000 plants in this second generation. • Three-fourths of the plants were as tall as the tall plants in the parent and first generations.

27. Section 10.1 Summary – pages 253-262 The second generation P1 • One-fourth of the offspring were as short as the short plants in the parent generation. Short pea plant Tall pea plant F1 • In the second generation, tall and short plants occurred in a ratio of about three tall plants to one short plant. All tall pea plants F2 3 tall: 1 short

28. Section 10.1 Summary – pages 253-262 The second generation • The original parents, the true-breeding plants, are known as the P1 generation. • The offspring of the parent plants are known as the F1 generation. • When you cross two F1 plants with each other, their offspring are the F2 generation.

29. Section 10.1 Summary – pages 253-262 The second generation Seed shape Flower color Pod color Seed color Flower position Pod shape Plant height Dominant trait axial (side) purple yellow green round tall inflated Recessive trait terminal (tips) green short white yellow wrinkled constricted

30. Section 10.1 Summary – pages 253-262 The second generation • In every case, he found that one trait of a pair seemed to disappear in the F1 generation, only to reappear unchanged in one-fourth of the F2 plants.

31. Section 10.1 Summary – pages 253-262 The rule of unit factors • Mendel concluded that each organism has two factors that control each of its traits. • We now know that these factors are genes and that they are located on chromosomes. • Alleles: different forms of a gene

32. Section 10.1 Summary – pages 253-262 The rule of unit factors • An organism’s two alleles are located on different copies of a chromosome—one inherited from the female parent and one from the male parent.

33. Section 10.1 Summary – pages 253-262 The rule of dominance • Dominant: the observed trait • Recessive: the trait that disappeared • Mendel concluded that the allele for tall plants is dominant to the allele for short plants.

34. Section 10.1 Summary – pages 253-262 The rule of dominance • When recording the results of crosses, it is customary to use the same letter for different alleles of the same gene. Short plant Tall plant t t T T t T F1 All tall plants t T

35. Section 10.1 Summary – pages 253-262 The rule of dominance • An uppercase letter is used for the dominant allele and a lowercase letter for the recessive allele. Short plant Tall plant t t T T t T F1 • The dominant allele is always written first. All tall plants t T

36. Section 10.1 Summary – pages 253-262 The law of segregation • The law of segregation states that every individual has two alleles of each gene and when gametes are produced, each gamete receives one of these alleles. • During fertilization, these gametes randomly pair to produce four combinations of alleles.

37. Section 10.1 Summary – pages 253-262 Phenotypes and Genotypes Law of segregation Tt´Tt cross • Two organisms can look alike but have different underlying allele combinations. F1 Tall plant Tall plant T t t T F2 Tall Tall Tall Short t t t t T T T T 3 1

38. Section 10.1 Summary – pages 253-262 Phenotypes and Genotypes • Phenotype: the way an organism looks and behaves • Genotype: the allele combination an organism contains • An organism’s genotype can’t always be known by its phenotype.

39. Section 10.1 Summary – pages 253-262 Phenotypes and Genotypes • Homozygous: An organism that has two alleles for a trait that are the same. • The true-breeding tall plant that had two alleles for tallness (TT) would be homozygous for the trait of height.

40. Section 10.1 Summary – pages 253-262 Phenotypes and Genotypes • Heterozygous: An organism that has two alleles for a trait that differ from each other. • Therefore, the tall plant that had one allele for tallness and one allele for shortness (Tt) is heterozygous for the trait of height.

41. Section 13.1 Summary – pages 337 - 340 Determining Genotypes • The genotype of an organism that is homozygous recessive for a trait is obvious to an observer because the recessive trait is expressed. • However, organisms that are either homozygous dominant or heterozygous for a trait controlled by Mendelian inheritance have the same phenotype.

42. Section 13.1 Summary – pages 337 - 340 Test crosses can determine genotypes • One way to determine the genotype of an organism is to perform a test cross. • Test cross: a cross of an individual of unknown genotype with an individual of known genotype. x ? dd Dd Dd d dd dd D

43. Section 13.1 Summary – pages 337 - 340 Test crosses can determine genotypes What are the possible results of a test cross? DD dd • If a known parent is homozygous recessive and an unknown parent is homozygous dominant for a trait, all of the offspring will be heterozygous and show the dominant trait. Homozygous x Homozygous d d Dd Dd D Dd Dd D Offspring: all dominant Dd

44. Section 13.1 Summary – pages 337 - 340 Test crosses can determine genotypes • If the organism being tested is heterozygous, the expected 1:1 phenotypic ratio will be observed. Dd dd Heterozygous x Homozygous d d Dd Dd D d dd dd • If any of the offspring, have the undesired trait, the parent in question must be heterozygous. Offspring: ½ dominant ½ recessive dd Dd

45. Section 10.1 Summary – pages 253-262 Mendel’s Dihybrid Crosses • Mendel performed another set of crosses in which he used peas that differed from each other in two traits rather than only one. • Such a cross involving two different traits is called a dihybrid cross.

46. Section 10.1 Summary – pages 253-262 The first generation • Mendel took true-breeding pea plants that had round yellow seeds (RRYY) and crossed them with true-breeding pea plants that had wrinkled green seeds (rryy). • He already knew the round-seeded trait was dominant to the wrinkled-seeded trait. • He also knew that yellow was dominant to green.

47. Section 10.1 Summary – pages 253-262 The first generation Dihybrid Cross round yellow x wrinkled green P1 Wrinkled green Round yellow All round yellow F1 F2 9 3 3 1 Round green Wrinkled yellow Round yellow Wrinkled green

48. Section 10.1 Summary – pages 253-262 The second generation • Mendel then let the F1 plants pollinate themselves. • He found some plants that produced round yellow seeds and others that produced wrinkled green seeds. • He also found some plants with round green seeds and others with wrinkled yellow seeds.

49. Section 10.1 Summary – pages 253-262 The second generation • He found they appeared in a definite ratio of phenotypes—9 round yellow: 3 round green: 3 wrinkled yellow: 1 wrinkled green.

50. Section 10.1 Summary – pages 253-262 The law of independent assortment • Mendel’s second law states that genes for different traits—for example, seed shape and seed color—are inherited independently of each other. • This conclusion is known as the law of independent assortment.