Interest Grabber. Analyzing Inheritance

Transcription

1 Interest Grabber Section 11-1 Analyzing Inheritance 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.

2 Interest Grabber continued Section 11-1 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 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?

3 Section Outline Section The Work of Gregor Mendel A. Gregor Mendel s Peas B. Genes and Dominance C. Segregation 1. The F 1 Cross 2. Explaining the F 1 Cross

4 Gregor Mendel s Peas Mendel was one of the first scientists to study genetics, the scientific study of heredity. Mendel carried out his research with ordinary garden pea plants. Peas are self-pollinating, which means that sperm cells in pollen fertilize the egg cells in the same flower. This process is called fertilization. Mendel used true-breeding pea plants as the basis of his experiments.

5 Mendel s Experiment Mendel wanted to produce seeds by joining the sperm and egg from different plants. In order to prevent self-pollination, Mendel cut away the pollen bearing male parts and dusted pollen from another plant onto the flower. This process is called cross-pollination. Mendel studied seven different pea plant traits. A trait is a specific characteristic such as seed color or plant height.

6 Section 11-1 Figure 11-3 Mendel s Seven F 1 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

7 Parental (P) Cross Mendel crossed two plants with contrasting traits, a tall plant with a short plant. This initial pair is called the Parental (P) generation. The offspring produced are called the First Filial (F 1 ) generation. The offspring of crosses between parents with different traits are called hybrids. The results of the cross produced all tall pea plants.

8 F 1 Cross Mendel drew 2 conclusions from the results. 1. Biological inheritance is determined by factors that are passed from one generation to the next. These factors are genes. 2. Mendel s principle of dominance which states that some alleles are dominant and others are recessive. Mendel wanted to find out if the short gene disappeared or was it hidden. Mendel self-pollinated the F 1 generation to produce a F 2 generation. The results produced 3 tall plants for every 1 short plant.

9 Principles of Dominance Section 11-1 P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short

10 Principles of Dominance Section 11-1 P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short

11 Principles of Dominance Section 11-1 P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short

12 Explanation of the F 1 Cross Mendel assumed the dominant allele masked the recessive allele. The reappearance of the recessive allele in the F 2 generation indicated the allele for shortness separated, or segregated, from the tall allele. Mendel assumed this happened during the formation of the gametes. The alleles segregate and each gamete contains only one allele.

13 Interest Grabber Section 11-2 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.

14 Interest Grabber continued Section 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?

15 Section Outline Section Probability and Punnett Squares A. Genetics and Probability B. Punnett Squares C. Probability and Segregation D. Probabilities Predict Averages

16 Genetics and Probability The likelihood that a particular event will occur is called probability. Take a coin flip of example, what are the chances of getting heads? Your chances are 1 in 2 flips or 1 : 2 or 50 percent. What are your chances to get 3 heads in a row? 1/2 X 1/2 X 1/2 = 1/8 The way in which alleles segregate is completely random. The principle of probability can be used to predict the outcomes of genetic crosses.

17 Punnett Squares A diagram that can show the gene combinations from a genetic cross. Organisms that have identical alleles for a trait are called homozygous. Organisms that have two different alleles for the same trait are heterozygous. Physical characteristics are called phenotypes. Genetic characteristics are called genotypes. Dominant traits are represented by capital letters, while recessive traits are represented by lower case letters.

18 Tt X Tt Cross Section 11-2

19 Tt X Tt Cross Section 11-2

20 Probabilities Predict Averages Probability can not predict the precise outcome of an individual event. However, they can predict the average outcome of a large event. The same holds true for genetics. The larger the number of offspring, the closer the resulting numbers will get to the predicted values.

21 Interest Grabber Section 11-3 Height in Humans Height in pea plants is controlled by one of 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 people? Are the factors that determine height more complicated in humans?

22 Interest Grabber continued Section Make a list of 10 adults whom you know. Next to the name of each adult, 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 2 alleles, as it is in pea plants? Explain your answer.

23 Section Outline Section Exploring Mendelian Genetics A. Independent Assortment 1. The Two-Factor Cross: F 1 2. The Two-Factor Cross: F 2 B. A Summary of Mendel s Principles C. Beyond Dominant and Recessive Alleles 1. Incomplete Dominance 2. Codominance 3. Multiple Alleles 4. Polygenic Traits D. Applying Mendel s Principles E. Genetics and the Environment

24 Two Factor Crosses

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26 Figure Independent Assortment in Peas Section 11-3

27 Concept Map Section 11-3 Gregor Mendel experimented with concluded that Pea plants Factors determine traits Some alleles are dominant, and some alleles are recessive Alleles are separated during gamete formation which is called the which is called the Law of Dominance Law of Segregation

28 Incomplete Dominance A scenario where neither gene is dominant over the other. Example: Red snapdragon crossed with a white snapdragon produces a pink snapdragon.

29 Section 11-3 Figure Incomplete Dominance in Four O Clock Flowers

30 Section 11-3 Figure Incomplete Dominance in Four O Clock Flowers

31 Codominance A situation where both alleles contribute to the phenotype. Example: Certain chickens with black feathers crossed with a chicken with white feathers produces an offspring with both black and white feathers. X =

32 Multiple Alleles Genes that have more than two alleles for a gene. Examples: Blood types in humans: A, B, AB, or O Human hair or eye color Fur color in rabbits Full Color Chinchilla Himalayan Albino

33 Polygenic Traits Traits that are controlled by two or more genes. Example: Human skin colors

34 Interest Grabber Section 11-4 How Many Chromosomes? 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. Working with a partner, discuss and answer the questions that follow.

35 Interest Grabber continued Section 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?

36 Section Outline Section Meiosis A. Chromosome Number B. Phases of Meiosis 1. Meiosis I 2. Meiosis II C. Gamete Formation D. Comparing Mitosis and Meiosis

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38 Crossing-Over Section 11-4

39 Crossing-Over Section 11-4

40 Crossing-Over Section 11-4

41 Figure Meiosis Section 11-4 Meiosis I

42 Figure Meiosis Section 11-4 Meiosis I

43 Figure Meiosis Section 11-4 Meiosis I

44 Figure Meiosis Section 11-4 Meiosis I

45 Figure Meiosis Section 11-4 Meiosis I

46 Figure Meiosis II Section 11-4 Meiosis II Prophase II Metaphase II Anaphase II Telophase II Meiosis I results in two The chromosomes line up in a haploid (N) daughter cells, similar way to the metaphase each with half the number of stage of mitosis. chromosomes as the original. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells.

47 Figure Meiosis II Section 11-4 Meiosis II Prophase II Metaphase II Anaphase II Telophase II Meiosis I results in two The chromosomes line up in a haploid (N) daughter cells, similar way to the metaphase each with half the number of stage of mitosis. chromosomes as the original. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells.

48 Figure Meiosis II Section 11-4 Meiosis II Prophase II Metaphase II Anaphase II Telophase II Meiosis I results in two The chromosomes line up in a haploid (N) daughter cells, similar way to the metaphase each with half the number of stage of mitosis. chromosomes as the original. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells.

49 Figure Meiosis II Section 11-4 Meiosis II Prophase II Metaphase II Anaphase II Telophase II Meiosis I results in two The chromosomes line up in a haploid (N) daughter cells, similar way to the metaphase each with half the number of stage of mitosis. chromosomes as the original. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells.

50 Figure Meiosis II Section 11-4 Meiosis II Prophase II Metaphase II Anaphase II Telophase II Meiosis I results in two The chromosomes line up in a haploid (N) daughter cells, similar way to the metaphase each with half the number of stage of mitosis. chromosomes as the original. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells.

51 Gamete Formation

52 Interest Grabber Section 11-5 Forever Linked? Some genes appear to be inherited together, or linked. If two genes are found on the same chromosome, does it mean they are linked forever? Study the diagram, which shows four genes labeled A E and a e, and then answer the questions on the next slide.

53 Interest Grabber continued Section In how many places can crossing over result in genes A and b being on the same chromosome? 2. In how many places can crossing over result in genes A and c being on the same chromosome? Genes A and e? 3. How does the distance between two genes on a chromosome affect the chances that crossing over will recombine those genes?

54 Section Outline Section Linkage and Gene Maps A. Gene Linkage B. Gene Maps

55 Comparative Scale of a Gene Map Section 11-5 Earth Mapping of Earth s Features Cell Mapping of Cells, Chromosomes, and Genes Country Chromosome State Chromosome fragment City Gene People Nucleotide base pairs

56 Figure Gene Map of the Fruit Fly Section 11-5 Exact location on chromosomes Chromosome 2

57 Videos Click a hyperlink to choose a video. Meiosis Overview Animal Cell Meiosis, Part 1 Animal Cell Meiosis, Part 2 Segregation of Chromosomes Crossing Over

58 Video 1 Meiosis Overview Click the image to play the video segment.

59 Video 2 Animal Cell Meiosis, Part 1 Click the image to play the video segment.

60 Video 3 Animal Cell Meiosis, Part 2 Click the image to play the video segment.

61 Video 4 Segregation of Chromosomes Click the image to play the video segment.

62 Video 5 Crossing Over Click the image to play the video segment.

63 Go Online The latest discoveries in genetics Interactive test Articles on genetics For links on Punnett squares, go to and enter the Web Code as follows: cbn For links on Mendelian genetics, go to and enter the Web Code as follows: cbn For links on meiosis, go to and enter the Web Code as follows: cbn-4114.

64 Interest Grabber Answers 1. In the first generation of each experiment, how do the characteristics of the offspring compare to the parents characteristics? All offspring had the same characteristic, which was like one of the parents. The other characteristic seemed to have disappeared. 2. How do the characteristics of the second generation compare to the characteristics of the first generation? Both characteristics appeared in this generation. The characteristic that had disappeared in the first generation did not appear as often as the other characteristic. (It appears about 25 percent of the time.)

65 Interest Grabber Answers 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? Results will vary, but should be close to 5 heads and 5 tails. 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? The results for 20 tosses may be closer to the predicted 10 heads and 10 tails. 3. If you compiled the results for the whole class, what results would you expect? The results for the entire class should be even closer to the number predicted by the rules of probability. 4. How do the expected results differ from the observed results? The observed results are usually slightly different from the expected results.

66 Interest Grabber Answers 1. Make a list of 10 adults whom you know. Next to the name of each adult, write his or her approximate height in feet and inches. Check students answers to make sure they are realistic. 2. What can you observe about the heights of the ten people? Students should notice that there is a range of heights in humans. 3. Do you think height in humans is controlled by 2 alleles, as it is in pea plants? Explain your answer. No, height does not seem to be controlled by two alleles, as it is in pea plants. Height in humans can vary greatly and is not just found in tall and short phenotypes.

67 Interest Grabber Answers 1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis? 46 chromosomes 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? = 92; a developing embryo would not survive if it contained 92 chromosomes. 3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have? Sperm and egg should each have 23 chromosomes.

68 Interest Grabber Answers 1. In how many places can crossing over result in genes A and b being on the same chromosome? One (between A and B) 2. In how many places can crossing over result in genes A and c being on the same chromosome? Genes A and e? Two (between A and B and A and C); Four (between A and B, A and C, A and D, and A and E) 3. How does the distance between two genes on a chromosome affect the chances that crossing over will recombine those genes? The farther apart the genes are, the more likely they are to be recombined through crossing over.

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