The Work of Gregor Mendel

1. The Work of Gregor Mendel Chapter 11

2. In Your Notebook • Fill out the Genetic Profile • Which character traits were you like the majority of the class? Name at least 3. • Which character traits were you in the minority? Name at least 2. • Where did you get these traits?

3. Who Is Gregor Mendel? • The father of modern genetics • Born in 1822 in Czech Republic • Became priest • Studied science & math at U. of Vienna • Worked in monastery – taught high school • Was in charge of monastery gardens

4. Mendel’s Experiments • Used garden peas • Small • Easy to grow • Produce a lot of offspring • Wanted to know how an organism gets its unique characteristics • Heredity – passing of characteristics from parent to offspring

5. Role of Fertilization • Male part of flower makes pollen (sperm) • Female part produces eggs • Fertilization • Joining of male and female reproductive cells to produce a new cell

6. Types of Fertilization • Self Pollination • Sperm cells fertilize egg cells within same flower • One parent • Offspring get all traits from one parent • Cross Pollination • Two parents • Cut off male parts so it couldn’t self pollinate then dusted plant with other pollen

7. Mendel’s Task • Studied seven traits • Self pollinated plants to get pure stock • He always knew outcome • Trait – specific characteristic (seed color) • Then cross pollinated to see what would happen • Hybrid – offspring of crosses between parents with different traits

8. Genes and Alleles Vocabulary • P = Parental generation • F1 = First Filial = kids • F2 = Second Filial = grandkids • Gene • Factors that are passed from parent to offspring • Alleles • Different forms of a gene • If studying trait of plant height one form of the gene produced tall plants and the other form of the gene produced short plants

9. Mendel’s Traits First experiment – cross pollinated plants - for each trait all the offspring had characteristics of only one parent – one trait disappeared

10. Mendel’s Conclusions • An individual’s characteristics are determined by factors that are passed from one parental generation to the next • Principle of Dominance • Some alleles are dominant and some are recessive • Since F1 generation plants were all tall he knew the tall allele was dominant and the short allele recessive

11. In Your Notebook • Write the dominant allele for seed shape. • Write the dominant allele for pod shape. • Write the recessive allele for flower position. • Write the recessive allele for seed coat.

12. F2 Generation • Mendel wanted to know what happened to the disappearing trait • Self pollinated F1 plants • Recessive trait showed up again

13. Explaining The Results • Decided reappearance of trait meant that, at some point, the allele for shortness had separated from the allele for tallness • Must have happened during formation of gametes (sperm and egg cells) • Law of Segregation • During gamete formation the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene

14. Explaining The Results • Dominant • capital letter (T) • Recessive • lower case letter (t)

15. In Your Notebook • You are Gregor Mendel • Tell me your story. • Who are you? • What experiments did you do? • What were your major findings? • At least three paragraphs with at least three sentences in each paragraph.

16. 11.2 What Are The Odds? • If you toss a coin, what is the probability of getting heads? Tails? If you toss a coin ten times, how many heads and how many tails would you 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 ten tosses.

17. In Your Notebook • 1. Assuming that you expect five heads and five tails in ten tosses, how do the results of your tosses compare? How about the results of your partner’s tosses? • 2. Add your results to those of your partner to produce a total of 20 tosses. Assuming that you expect ten heads and ten 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?

18. Probability and Punnett Squares • Probability • The likelihood that a certain event will occur • Predicts the average outcome of a large number of events • The larger the sample size, the more likely you are to match the expected results • Like tossing a coin twice and expecting one head and one tail vs. tossing it one hundred times

19. Vocabulary Words • Genotype • The genetic make-up of an individual • These are the letters • Phenotype • The physical traits of an individual • Tall, short, round, purple, etc. • Homozygous • The organism has two identical alleles • TT or tt • Heterozygous • The organism has two different alleles • Tt

20. Punnett Squares • Use mathematical probability to help predict the genotype and phenotype combinations in genetic crosses • Monohybrid Cross – looks at only one trait

21. Homozygous x Homozygous Flower Color Genotype White (pp) All = Pp p p P Phenotype Purple All = Purple (PP) P

22. Homozygous x Heterozygous Guinea Pig Homozygous Black = BB Genotype Heterozygous Black = Bb 50% = BB B b50% = Bb B Phenotype B 100% Black

23. Heterozygous x Heterozygous • Guinea Pig Genotype • Both heterozygous = Bb 25% = BB 50% = Bb B b 25% = bb B Phenotype b 75% = Black 25% = Brown

24. Independent Assortment • Mendel’s next question • Does the segregation of one set of alleles affect any others? • Does the gene that determines seed shape affect the gene for seed color? • Will the dominant genes always stay together? • Used Dihybrid cross • Looked at two genes

25. Independent Assortment

26. Independent Assortment Conclusions • Genes for different traits can segregate independently during the formation of gametes • The dominant traits don’t always stay together • Genes segregate independently and don’t influence one another • The only exception would be if the genes are really close to each other on the chromosome – then they might travel together • This is why you look different than your siblings even though you have the same parents

27. A Summary of Mendel’s Work • The inheritance of biological characteristics is determined by individual units called genes, which are passed from parents to offspring. • When two or more forms (alleles) of the gene for a single trait exist, some alleles may be dominant and others may be recessive. • In most sexually reproducing organisms, each adult has two copies of each gene – one from each parent. These genes segregate from each other when gametes are formed. • Alleles for different genes usually segregate independently of each other.

28. In Your Notebook • Explain the following statements: • A tall plant can be homozygous or heterozygous. A short plant must be homozygous. • One half of the F2 generation is heterozygous and one half is homozygous, but three fourths are tall and one fourth is short.

29. 11.3 Other Patterns of Inheritance • Discussion • Height in pea plants is controlled by two alleles; the allele for a tall plant is the dominant allele, while the allele for a short plant is the recessive one. • What about height in people? Are the factors that determine height more complicated in humans?

30. In Your Notebook • 1. Make a list of ten people whom you know. Next to the name of each person, write his or her approximate height in feet and inches. • 2. What can you observe about the heights of the ten people? • 3. Do you think height in humans is controlled by two alleles, as it is in pea plants? Explain your answer. • 4. What other traits in humans show a similar amount of variation between individuals?

31. Beyond Dominant and Recessive Alleles • All of Mendel’s rules have exceptions • Genetics is more complicated because there are usually more than two alleles for each trait • Also complicated because many traits are controlled by more than one gene

32. Incomplete Dominance • Some alleles are neither dominant or recessive • The heterozygous phenotype is in between • A red flower crossed with a white flower will produce pink flowers

33. Codominance • Both alleles are dominant • The heterozygous phenotype doesn’t mix – it shows both colors equally • Erminette Chickens and Roan Cows

34. Multiple Alleles • A gene with two or more alleles • Each individual has only two copies but within population there may be several different alleles • Rabbit’s coat color has at least four different alleles • Human blood type has three • A,B &O

35. In Your Notebook • Page 320 in your textbook • Read and answer the questions in the Analyzing Data section • Helpful Hints • A and B are codominant • O is recessive • The Rh factor is inherited separately from blood type • Rh+ is dominant

36. Polygenic Traits • Traits that are produced by the interaction of several genes • Show wide range of phenotypes • Example: human skin color

37. In Your Notebook • In your own words, describe multiple alleles and polygenic traits. • How are they similar? • How are they different?

38. Genes and the Environment • Does the environment have a role in how genes determine traits? • Genes provide a plan for development, but how that plan unfolds depends on the environment. • Butterflies hatching in spring have different wing patterns than those hatching in summer

39. In Your Notebook • Write a rap or poem using the following terms: • Incomplete Dominance • Codominance • Multiple Alleles • Polygenic Traits

40. 11.4 Meiosis • Mendel knew genes were carried on structures in the cells. Our next question is what structures are they carried on? • Normal human body cells each contain 46 chromosomes. The cell division process that body cells undergo is called mitosis and produces daughter cells that are virtually identical to the parent cell.

41. In Your Notebook • 1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis? • 2. If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain? Do you think this would create any problems in the developing embryo? • 3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have?

42. Chromosome Number • How many sets of genes do multicellular organisms inherit? • Two – One from mom and one from dad • The Rules • An organism with two parents must inherit a single copy of every gene from each parent • When that organism produces gametes, those two sets of genes must be separated so that each gamete (egg or sperm) has just one set of genes

43. Diploid Cells • Diploid • Two sets (2N) • The diploid cells of most adult organisms contain two complete sets of inherited chromosomes and two complete sets of genes • All of your cells are diploid except for sperm and egg cells • Homologous Chromosomes • A matching pair of chromosomes • The #1 chromosome from your dad and the #1 chromosome from your mom are homologous

44. Haploid Cells • Cells with only one set of chromosomes (1N) • These are the sperm and egg cells • Why do they only have one set? • If diploid number is 8 then haploid number is 4 • Human diploid number is 46 so haploid is 23

45. In Your Notebook • Page 327 • Read the Analyzing Data Section and answer the questions in your notebook

46. Phases of Meiosis • How are haploid cells produced from diploid cells? • Meiosis • The process in which the number of chromosomes per cell is cut in half • Homologous chromosomes are separated • Two phases • Meiosis I and Meiosis II

47. Meiosis I • The cell undergoes a round of chromosome replication during interphase – just like mitosis • Now you have two identical chromatids joined at the center

48. Prophase I • Each replicated chromosome pairs with its corresponding homologous chromosome forming tetrad • A tetrad has four chromatids • Crossing over occurs here and alleles get exchanged

49. Metaphase I and Anaphase I • Metaphase I • The chromosomes line up in the middle • Anaphase I • Spindle fibers pull each homologous chromosome pair toward opposite end of the cell

50. Telophase I and Cytokinesis • Telophase I • Nuclear membrane forms around each cluster of chromosomes • Cytokinesis • Cytoplasm splits and two new cells are formed