PATTERNS OF INHERITANCE

1. PATTERNS OF INHERITANCE GENETICS DEVELOPED FROM CURIOSITY ABOUT INHERITANCE

2. GENETICS DEVELOPED FROM CURIOSITY ABOUT INHERITANCE • The Blending Hypothesis of Inheritance • Traits are variations of particular characteristics. • One plant might have red flowers, while another might have purple flowers. • The hypothesis in the early 1800s was the blending hypothesis, which explained how offspring inherited traits from both parents. • Crossing yellow and red flowered plants would produce orange flowered plants.

3. GENETICS DEVELOPED FROM CURIOSITY ABOUT INHERITANCE • All offspring would then be orange. • This hypothesis was proven wrong after red flowered plants produced yellow flowers and some traits would disappear from one generation to the next. • Mendel’s Plant Breeding Experiments • Gregor Mendel, a priest, was one of the first to use the scientific method to the subject of inheritance, giving rise to genetics, the study of heredity.

4. GREGOR MENDEL

5. GENETICS DEVELOPED FROM CURIOSITY ABOUT INHERITANCE • Mendel developed the particulate hypothesis of inheritance after working with pea plants for seven years. • According to the hypothesis, parents pass on to their offspring genes responsible for the inherited traits. • These heritable factors retain their identity from generation to generation. • Mendel first identified true breeding plants that produced identical offspring in each generation after self fertilization.

6. GENETICS DEVELOPED FROM CURIOSITY ABOUT INHERITANCE • Purple always produced purple and white always produced white. • A bag was tied around each flower to prevent cross pollination. • He then crossed the true breeding purple plant with the true breeding white plant. In a process called cross-fertilization. • Sperm of one plant fertilizes the eggs of a different plant. • He then wondered what the offspring traits would be (flower colors).

7. MENDEL’S FERTILIZATION TECHNIQUE

8. DIFFERENT PEA PLANT TRAITS

9. REVIEW: CONCEPT CHECK 10.1, page 207 • Explain how Mendel’s particulate hypothesis is different from the blending hypothesis of inheritance. • What is the difference between self-fertilization and cross-fertilization? • Describe a pattern of inheritance that the blending hypothesis fails to explain.

10. MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE • Mendel’s Principle of Segregation • The offspring of two true breeding specimens are hybrids. • The parents are the P generation and the first offspring the F₁ generation for filial. • The F₂ generation is the product of the F₁ self-fertilizing. • In one experiment, Mendel crossed purple flowered plants with white flowered plants, or a monohybrid cross where the parents differ in only one character.

11. P, F₁, & F₂ GENERATIONS

12. DOMINANT vs. RECESSIVE TRAITS

13. P, F₁, & F₂ GENERATIONS

14. P, F₁, & F₂ GENERATIONS

15. MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE • The F₁ hybrids were all purple. • The F₂, after self-fertilization, were ¾ purple and ¼ white. • Mendel concluded that there were two factors for flower color, purple and white, each now called genes. • As seen in previous pictures, there were other characteristics in the pea plants that Mendel studied. • The same pattern appeared in each F₁ generation.

16. MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE • As a result, Mendel developed four hypothesis (use gene instead of factor): • There are alternative forms of genes (the gene for flower color was purple in one form and white in another) or alleles. • For each inherited character, the organism has two alleles for the gene that controls that character, one from each parent. • Both alleles the same, the individual is homozygous. • Both alleles different, the individual is heterozygous.

17. MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE 3. The trait is dominant if only one of the two different alleles affect or present that trait in the offspring, with the allele being recessive, or non-appearing. 4. The two alleles for a character segregate (separate) during the formation of gametes (sex cells) with each gamete carrying only one allele for each character. a. This is Mendel’s principle of segregation. b.As the gametes join during fertilization, allele pairs reform in the offspring.

18. MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE • Probability and Punnett Squares • Crossing true-breeding (homozygous) purple with white flowers will result in a purple (dominant) flower, P Purple(PP) X White(pp) F₁ Purple(Pp) where P is dominant and p is recessive, and is heterozygous.

19. PENNY PROBABILITIESX axis: 2 sides of penny 2 (½H + ½T)Y axis: 2 sides of penny 1 (½H + ½T)

20. PUNNETT SQUARES

21. MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE • When the F₁ generation reproduces, each gamete will receive only one allele for flower color, P or p, with equal likelihood. • The gametes will combine randomly and form zygotes or pairs of alleles. • The likelihood or probability of each pair forming is key to the inheritance pattern in F₂. • Punnett squares aid in the calculation of probabilities by using grid patterns by showing all the possible outcomes of a genetic cross.

22. MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE • Genotype and Phenotype • Looking at the F₂ generation, the probabilities using the Punnett square shows that ¼ of the F2 plants are homozygous for purple allele (PP). • ½ (¼ +¼) of the F₂ are heterozygous (Pp), and be purple, the dominant color. • ¼ of the F₂ will be homozygous for the recessive trait (pp) and be white.

23. MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE • Therefore, according to Mendel’s hypothesis, the probabilities are ¾:¼ or 3:1, flower color (purple to white). • The phenotype is the observable trait and the genotype is the genetic makeup, or combination of alleles (PP, Pp, pp). • The phenotypic ratio is 3 purple to 1 white and the genotypic ratio is 1(PP):2(Pp):1(pp).

24. MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE • The Testcross • A question arises when trying to determine the genotype of an organism. • For example, if a flower is purple, is it PP or Pp? • To determine this, a testcross is done, which is breeding an individual of an unknown genotype, but dominant phenotype, with a homozygous recessive individual.

25. TESTCROSS

26. TESTCROSS

27. MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE • The appearance of the cross will reveal the genotype of the mystery plant. • This is because the homozygous recessive plant (pp) can contribute only a recessive allele to the offspring, therefore the phenotype will specify the allele contributed by the mystery plant. • Mystery homozygous (PP) X homozygous recessive (pp) yields heterozygous purple (Pp). • Mystery heterozygous (Pp) X homozygous recessive (pp) yields purple (Pp) and white (pp).

28. MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE • Mendel’s Principle of Independent Assortment • Mendel studied seven characteristics of the peas, including shape and color. • Round shape dominant to wrinkled • Yellow color dominant to green • How about a dihybrid cross, that is, crossing organisms differing in two characters?

29. DIHYBRID CROSS

30. DIHYBRID CROSS

31. DIHYBRID CROSS

32. MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE • Mendel crossed true breeding round yellow seeds (RRYY) with true breeding wrinkled green seeds (rryy). • The first parent produced only RY gametes, the other ry. • The union produced RrYy, hybrid heterozygotes, with all having the dominant phenotype, round and yellow. • The hybrids grew into the F₁ plants, and were allowed to self-fertilize.

33. MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE • Four phenotypes were produced in the F₂, RY, rY, Ry, and ry, a ratio of 9 : 3 : 3 : 1. • In fact, looking at the dihybrid Punnett square, this shows the same outcome as two monohybrid crosses occurring at the same time. • Seed shape alone shows 12 plants with round seeds to every 4 with wrinkled seeds, which is the 3 : 1 seen in the monohybrid F₂ generation. • Mendel tested every pea characteristic in the dihybrid form and found that the 9:3:3:1 ratio persisted.

34. MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE • As a result Mendel proposed the principle of independent assortment. • This states that gamete formation in F₂ crosses, a particular allele for one character can be paired with either allele of another character (R with a Y or y, r with a Y or y).

35. REVIEW: CONCEPT CHECK 10.2, page 213 1. What are the two possible gametes produced by a plant that has the genotype Aa? Give the probability of each type of gamete. 2. Use a Punnett square to predict the genotypes produced if the plant in Question 1is self-fertilized. Calculate the probability of each outcome. 3. List all the possible genotypes of a pea plant with purple flowers and round seeds. 4. List the four possible allele combinations in the gametes of a plant with genotype PpWw.

36. THERE ARE MANY VARIATIONS OF INHERITANCE PATTERNS • Intermediate Inheritance • In the F₁ generations of Mendel, all the specimens looked like the dominant homozygous parent because there was one dominant allele to produce the dominant phenotype. • To see the recessive phenotype required two recessive alleles. • Some traits in organisms have neither allele as dominant.

37. THERE ARE MANY VARIATIONS OF INHERITANCE PATTERNS • In these cases, the phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes, or is the intermediate inheritance. • A prime example is the Andalusian chicken. • Black and white parents produce an F₁ hybrid called “blues” that have grayish-blue feathers. • Neither the black nor white allele is dominant, capital and lower case letters are not used. • C & B with a superscript B or W are used (Cb or BW), with the heterozygous chicken being CB CW , and blue.

38. INTERMEDIATE INHERITANCE

39. THERE ARE MANY VARIATIONS OF INHERITANCE PATTERNS • This is not the blending hypothesis because the parent phenotypes can reappear in the F₂ generation. • In the picture previously, the predicted phenotypes in the F₂ are 1 black: 2 blue: 1 white, and this ratio 1:2:1 is also the genotype. • Multiple Alleles • We have looked at no more than two contrasting alleles for each inherited character, but in populations several alleles exist for genes.

40. THERE ARE MANY VARIATIONS OF INHERITANCE PATTERNS • This expands the number of possibilities of genotypes and phenotypes. • Multiple alleles account for blood types. • These typically are A, B, AB, or O with the letter referring to the two carbohydrates (A and B) found on the surface of red blood cells (rbc). • So, a person’s rbc can be coated with one carbohydrate (type A), or the other (type B), both (type AB), or none (type O). • In the illustration to follow, there are various combinations for the three alleles. • IA (for carbohydrate A) • IB (for carbohydrate B) • i (for neither A or B)

41. BLOOD TYPE ALLELES

42. THERE ARE MANY VARIATIONS OF INHERITANCE PATTERNS • Each person inherits one of the alleles from each parent, with six possible ways to pair the alleles, or six possible genotypes. • The alleles IA and IB exhibit codominance, or a heterozygote expresses both traits. • This is different from intermediate inheritance because the phenotype is not intermediate but shows separate traits of both alleles. • Polygenic Inheritance • Mendel’s pea plants exhibited seven characters that occurred in two phenotypes.

43. THERE ARE MANY VARIATIONS OF INHERITANCE PATTERNS • Sometimes, intermediate inheritance, codominance of alleles, or multiple types of alleles can lead to more than two phenotypes in a population. • Multiple genes affecting characters leads to much variation in phenotypes. • Polygenic inheritance is when two or more genes affect a single character. • Height and skin color are just two examples. • There could be 3 tall alleles (A, B, C) and 3 short alleles (X, Y, Z).

44. POLYGENIC INHERITANCE

45. THERE ARE MANY VARIATIONS OF INHERITANCE PATTERNS • AABBCC would be the tallest, AXBBCC maybe next, and XXYYZZ the shortest. • The number of genes that affect a character increases the potential combination of alleles. • The Importance of Environment • Environment has an affect on phenotype. • Trees and plants are examples where leaves, shape, and greenness are affected by wind and sunlight.

46. THERE ARE MANY VARIATIONS OF INHERITANCE PATTERNS • Temperature can affect the fur color of a Siamese cat, where black is found on the ears, face, feet, and tail because these are cooler where black is predominant. • Nutrition can affect height, exercise body status, sunlight darkens skin. • The environment can even affect identical twins. • Blood type is not affected by environment but oxygen carrying capacity can be.

47. PHENOTYPES AND THE ENVIRONMENT

48. REVIEW: CONCEPT CHECK 10.3, page 217 • For a trait with intermediate inheritance, what is the phenotypic ratio for F₂ offspring of a monohybrid cross? How is that different from a simple dominant-recessive cross? • Two parents have O blood. What blood type would you expect for their child? • What is the likely mechanism for inheritance for a character with large range of phenotypes? Explain. • Give three examples of human physical characters affected by environment.

49. MEIOSIS EXPLAINS MENDEL’S PRINCIPLES • Chromosome Theory of Inheritance • From the 1800s to the beginning of the 20th century, scientists discovered mitosis and meiosis and saw the similarities between the behavior of chromosomes and Mendel’s heritable factors. • From this came the chromosome theory of inheritance, which states that genes are located on chromosomes, and the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns.

50. MEIOSIS EXPLAINS MENDEL’S PRINCIPLES • Remember, during meiosis the chromosomes undergo segregation and independent assortment, Mendel’s two primary principles. • Every diploid individual, pea plants or humans, have two sets of homologous chromosomes. • One from the male • One from the female • The alleles of a gene are in the same location on the homologous chromosomes, or gene locus.