Analyzing Inheritance

1. Section 11-1 Analyzing Inheritance Interest Grabber • Offspring resemble their parents. Offspring inherit genes for characteristics from their parents. To learn about inheritance, scientists have experimented with breeding various plants and animals. • In each experiment shown in the table on the next slide, two pea plants with different characteristics were bred. Then, the offspring produced were bred to produce a second generation of offspring. Consider the data and answer the questions that follow. Go to Section:

2. Parents Long stems  short stems Red flowers  white flowers Green pods  yellow pods Round seeds  wrinkled seeds Yellow seeds  green seeds First Generation All long All red All green All round All yellow Second Generation 787 long: 277 short 705 red: 224 white 428 green: 152 yellow 5474 round: 1850 wrinkled 6022 yellow: 2001 green Section 11-1 • 1. In the first generation of each experiment, how do the characteristics of the offspring compare to the parents’ characteristics? • 2. How do the characteristics of the second generation compare to the characteristics of the first generation? Go to Section:

3. Section 11-1 • 11–1 The Work of Gregor Mendel A. Gregor Mendel’s Peas B. Genes and Dominance C. Segregation • 1. The F1 Cross • 2. Explaining the F1 Cross Go to Section:

4. KEY CONCEPT Mendel’s research showed that traits are inherited as discrete units.

5. Heredity: The transmission of traits from parents to offspring. Who was Gregor Mendel? Austrian monk and high school teacher born in 1822. Father of Genetics (1800’s) study of heredity Modern genetics is a core theme in biology.

6. Mendel laid the groundwork for genetics. • Traits are distinguishing characteristics that are inherited. • Genetics is the study of biological inheritance patterns and variation. • Gregor Mendel showed that traits are inherited as discrete units. • Many in Mendel’s day thought traits were blended.

7. Mendel’s data revealed patterns of inheritance. • Mendel made three key decisions in his experiments. • use of purebred plants • control over breeding • observation of seven“either-or” traits

8. 4 stock plants: • Tall/Short Green/Yellow seeds • The peas were self pollinating and producing an exact copy of the parent plant. (True Breeding) • Mendel cross bred the seeds and got hybrid pea plants. • How ? He took pollen from the male structures (anthers) of a tall plant and placed it on the female structures (pistil) of a short plant. • All of the offspring were hybrid tall (F1).

9. To really appreciate Mendel, we have to keep in mind what people thought at the time. Blended Inheritance – that sperm and egg traits mixed to form a intermediate offspring. If one parent tall and one short, offspring will be in between or medium height.

10. A. Mendel’s Peas Chose garden peas to test. Why? • Grow quickly and easily in very little space. • True-breeding peas - all offspring show the same trait generation after generation (homozygous). • Variety of contrasting traits to study (tall v short, white v purple, etc.) • Easy to control breeding because closed flower doesn’t let random sperm/pollen in!

11. 1. Grow easily and quickly. • Could get at least 2 crops per year • Now we use flies or bacteria

12. 2. True-breeding (Pure bred) predict offspring traits reliably from pure bred stock. Tall x Tall always = tall offspring

13. 3. Variety of contrasting Traits • One stock of seeds would produce only tall plants, another only short ones. • Mendel studied 7 individual traits Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short

14. 4. Easy to control breeding • male & female parts are in a closed flower – other plant pollen can’t get in. a) self-pollinate – fertilization in a single plant using own pollen (sperm) and egg to make a zygote (seed!)

15. Mendel wanted to study the results of breeding 2 different plants, so he had to prevent self-pollination. b) cross-pollination breeding two different plants

16. Checkpoint • What does it mean if an organism is true breeding? • What is the difference between self-pollination and cross-pollination? ANY QUESTIONS?

17. Mendel controlled the fertilization of his pea plants by removing the male parts, or stamens. He then fertilized the female part, or pistil, with pollen from a different pea plant. • Mendel used pollen to fertilize selected pea plants. • P generation crossed to produce F1 generation • interrupted the self-pollination process by removing male flower parts

18. B.Mendel’s experiments Mendel studied 7 different traits. What is a trait? A specific inheritable characteristic. P Generation are the parent plants. F1 Generation are the 1st generation plants. F2 Generation are the 2nd generation plants. Cross bred plants and studied the results using math. Can’t study them all at once Mendel studied one trait at a time (1 variable) = good science!

19. Section 11-1 Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall Go to Section:

20. Bred true breeding plants. • True tall to true short. • P = true breeding parents (homozygous) • Tall x short b) F1 = first filial (offspring of P, heterozygous) • all tall F2 –second filial P - parent F1 –first filial

21. 2. Bred F1 x F1 F2 = second filial (offspring of F1) • 3 tall:1 short F2 –second filial P - parent F1 –first filial

22. What did Mendel expect? • He expected medium plants! Blended inheritance was the dominant theory. Instead he got all tall in F1 and then roughly 3 tall for each short in F2. • How did short go away and then come back in a later generation?

23. What did Mendel do? • Repeat! Repeat! Repeat! = Good Science • He counted over a thousand plants for height alone! Still ~ 3:1 ratio

24. What do the results mean? Had the short allele disappeared? Was it gone or was it still there in the F1 plants? How did he know? • Still present, because it showed up in the F2 • AND it was unchanged. Short expression same as short purebred when seen again! • Means Short and Tall are different versions of the same trait and do not get mixed together.

25. Mendel’s work led to 2 laws. • The law of segregation: Members of each pair of alleles separate when the gametes are formed. (Homologous Chromosomes separate) • The law of independent assortment: Pairs of alleles separate independently of one another during gamete formation.

26. What do the results mean? • Genes/traits are passed unchanged as a unit No blending! Genes – DNA sequence on a chromosome that codes for specific protein(s) that determine traits (The chemical factors that determine traits.) Alleles - different expressions of same gene for same trait Ex: one allele codes for tall, one allele codes for short but both the same gene coding for height

27. What do the results mean? • Segregation of alleles – during gamete formation, alleles separate so you only inherit one copy of each gene from each parent • F1 had to have both alleles to get a short plant in F2, so the allele for shortness had to be separated from the allele for tallness when passed to the F2. • homologous chromosomes must separate • When does this happen during sexual reproduction??? MEIOSIS! Anaphase I

28. Segregation of Alleles  Meiosis Fertilization

29. What do the results mean? 3. Principle of Dominance – one allele can mask another allele. Tall allele dominated short allele. Dominant – allele or trait that is seen when present, masks recessive allele. Capital letters: A Recessive – allele or trait that is only seen if the dominant trait is NOT present. Lower case letters: a

30. How do you tell which trait is dominant?

31. Checkpoint • What is the difference between a gene and an allele? • How did Mendel know that the F1 generation still had the allele for short? • How is the segregation of alleles related to meiosis? • What is the Principle of Dominance? ANY QUESTIONS?

32. Mendel observed patterns in the first and second generations of his crosses.

33. purple white • Mendel drew three important conclusions. • Traits are inherited as discrete units. • Organisms inherit two copies of each gene, one from each parent. • The two copies segregateduring gamete formation. • The last two conclusions arecalled the law of segregation.

34. Section 11-2 Interest Grabber Tossing Coins • If you toss a coin, what is the probability of getting heads? Tails? If you toss a coin 10 times, how many heads and how many tails would you expect to get? Working with a partner, have one person toss a coin • ten times while the other person tallies the results on a sheet of paper. Then, switch tasks to produce a separate tally of the second set of 10 tosses. Go to Section:

35. Interest Grabber continued Section 11-2 1. Assuming that you expect 5 heads and 5 tails in 10 tosses, how do the results of your tosses compare? How about the results of your partner’s tosses? How close was each set of results to what was expected? 2. Add your results to those of your partner to produce a total of 20 tosses. Assuming that you expect 10 heads and 10 tails in 20 tosses, how close are these results to what was expected? 3. If you compiled the results for the whole class, what results would you expect? 4. How do the expected results differ from the observed results? Go to Section:

36. Section 11-2 Section Outline • 11–2 Probability and Punnett Squares A. Genetics and Probability B. Punnett Squares C. Probability and Segregation D. Probabilities Predict Averages Go to Section:

37. Genes and Physical Traits • Genotype – genetic makeup of alleles • Geno = “genes” • Ex: AA, Aa or aa; dominant or recessive, heterozygous or homozygous • Phenotype– physical expression of traits or what organism looks like! • Pheno = “to show” • Ex: tall or short, green or yellow, blue eyes or brown eyes

38. Genotypes and Phenotypes are different. TALL TALL • All tall plants have the same phenotype, or physical characteristic of tallness. • They do not, however, have the same genotype, or genetic makeup (alleles!) • Same phenotype but different genotype. 

39. Determining Genotypes and Phenotypes. TALL TALL • Can we know phenotype if we know the genotype? • Why? • Can we know the genotype if we know the phenotype? • Why not?

40. Checkpoint • What are different forms of the same gene called? • For genotype TT, is this dominant or recessive? Homozygous or heterozygous? • What is the phenotype of a heterozygous plant if purple flowers dominate white flowers? ANY QUESTIONS?

41. KEY CONCEPT Genes encode proteins that produce a diverse range of traits.

42. What is homozygous? Having two identical alleles for a trait. Homozygous Dominant – two dominant alleles = AA Homozygous Recessive – two recessive alleles = aa What is heterozygous? Having two different alleles for a trait. = Aa

43. The same gene can have many versions. • A gene is a piece of DNA that directs a cell to make a certain protein. • Each gene has a locus, aspecific position on a pair ofhomologous chromosomes.

44. An allele is any alternative form of a gene occurring at a specific locus on a chromosome. • Each parent donates one allele for every gene. • Homozygous describes two alleles that are the same at a specific locus. • Heterozygous describes two alleles that are different at a specific locus.

45. Genes influence the development of traits. • All of an organism’s genetic material is called the genome. • A genotype refers to the makeup of a specific set of genes. • A phenotype is the physical expression of a trait.

46. Alleles can be represented using letters. • A dominant allele is expressed as a phenotype when at least one allele is dominant. • A recessive allele is expressed as a phenotype only when two copies are present. • Dominant alleles are represented by uppercase letters; recessive alleles by lowercase letters.

47. Both homozygous dominant and heterozygous genotypes yield a dominant phenotype. • Most traits occur in a range and do not follow simple dominant-recessive patterns.

48. KEY CONCEPT The inheritance of traits follows the rules of probability.

49. What is probability? • The likelihood that an event will occur. Usually expressed in a ratio. • Probability can be used to predict the outcome of genetic crosses. • What is a Punnett Square? • A diagram that shows the segregation of genes.

50. Probability and Punnet Squares • Whenever Mendel crossed two hybrid plants (F1), he got 3:1 ratio or ¾ dominant and ¼ recessive. • Mendel realized that the principles of probability (MATH!!) could be used to explain the results of genetic crosses.