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The authors note that Mendel’s work was published in 1866, seven years after Darwin published Origin of Species. Consider challenging your students to consider whether Mendel’s findings supported Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet, Mendel’s selection of pea plant traits typically showed complete dominance, rather than the possibility for such gradual inheritance.

Teaching Tips

1. In Module 9.2, the authors make the analogy between genes and playing cards, noting that each are shuffled but retain their original identity. This analogy may form a very useful reference point for your students and can be used later, as new principles of genetics are discussed.

2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress.

The authors note that Mendel’s work was published in 1866, seven years after Darwin published Origin of Species. Consider challenging your students to consider whether Mendel’s findings supported Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet, Mendel’s selection of pea plant traits typically showed complete dominance, rather than the possibility for such gradual inheritance.

Teaching Tips

1. In Module 9.2, the authors make the analogy between genes and playing cards, noting that each are shuffled but retain their original identity. This analogy may form a very useful reference point for your students and can be used later, as new principles of genetics are discussed.

2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress.

The authors note that Mendel’s work was published in 1866, seven years after Darwin published Origin of Species. Consider challenging your students to consider whether Mendel’s findings supported Darwin’s ideas. Some scientists have noted that Darwin often discussed the evolution of traits by matters of degree. Yet, Mendel’s selection of pea plant traits typically showed complete dominance, rather than the possibility for such gradual inheritance.

Teaching Tips

1. In Module 9.2, the authors make the analogy between genes and playing cards, noting that each are shuffled but retain their original identity. This analogy may form a very useful reference point for your students and can be used later, as new principles of genetics are discussed.

2. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress.

Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. We would expect that any six playing cards dealt might be half black and half red, but we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling will reflect expected ratios.

Teaching Tips

1. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress.

2. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP pp and (b) Pp pp.

3. For students struggling with basic terminology, an analogy between a genetic trait and a pair of shoes might be helpful. A person might wear a pair of shoes in which both shoes match (homozygous), or less likely, a person might wear shoes that do not match (heterozygous).

4. Another analogy that might help struggling students is a pair of people trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. This (heterozygous) couple eats at home (the dominant allele “wins”).

Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. We would expect that any six playing cards dealt might be half black and half red, but we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling will reflect expected ratios.

Teaching Tips

1. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress.

2. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP pp and (b) Pp pp.

3. For students struggling with basic terminology, an analogy between a genetic trait and a pair of shoes might be helpful. A person might wear a pair of shoes in which both shoes match (homozygous), or less likely, a person might wear shoes that do not match (heterozygous).

4. Another analogy that might help struggling students is a pair of people trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. This (heterozygous) couple eats at home (the dominant allele “wins”).

Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. We would expect that any six playing cards dealt might be half black and half red, but we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling will reflect expected ratios.

Teaching Tips

1. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress.

2. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP pp and (b) Pp pp.

3. For students struggling with basic terminology, an analogy between a genetic trait and a pair of shoes might be helpful. A person might wear a pair of shoes in which both shoes match (homozygous), or less likely, a person might wear shoes that do not match (heterozygous).

4. Another analogy that might help struggling students is a pair of people trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. This (heterozygous) couple eats at home (the dominant allele “wins”).

Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. We would expect that any six playing cards dealt might be half black and half red, but we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling will reflect expected ratios.

Teaching Tips

1. This early material introduces many definitions that are vital to understanding the later discussions in this chapter. Therefore, students need to be encouraged to master these definitions immediately. This may be a good time for a short quiz to encourage their progress.

2. Many students benefit from a little quick practice with a Punnett square. Have them try these crosses for practice: (a) PP pp and (b) Pp pp.

3. For students struggling with basic terminology, an analogy between a genetic trait and a pair of shoes might be helpful. A person might wear a pair of shoes in which both shoes match (homozygous), or less likely, a person might wear shoes that do not match (heterozygous).

4. Another analogy that might help struggling students is a pair of people trying to make a decision about where to eat tonight. One person wants to eat at a restaurant, the other wants to eat a meal at home. This (heterozygous) couple eats at home (the dominant allele “wins”).

Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. We would expect that any six playing cards dealt might be half black and half red, but we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling will reflect expected ratios.

Teaching Tips

Many students have trouble with the basic statistics that are necessary for many of these calculations. Give your students some practice. Consider having them work in pairs, each with a pair of dice (for large class sizes, this can be done in laboratories). Let them calculate the odds of rolling three sixes in a row and other possibilities.

Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. We would expect that any six playing cards dealt might be half black and half red, but we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling will reflect expected ratios.

Teaching Tips

Figure 9.4 can be of great benefit when introducing genetic terminology. For students struggling to think abstractly, such a visual aid may be essential when describing these features in lecture.

This section of the chapter relies upon a good understanding of the chromosome-sorting process of meiosis. If students were not assigned Chapter 8, and meiosis has not otherwise been addressed, it will be difficult for students to understand the chromosomal basis of inheritance or linked genes.

Teaching Tips

Figure 9.16 requires an understanding of meiosis and the general cell cycle from Chapter 8. Students may need to be reminded that chromosomes are duplicated in the preceding interphase, as indicated in the first step. Furthermore, students may not initially notice that this diagram represents four possible outcomes, not stages of any one meiotic cycle.

Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. We would expect that any six playing cards dealt might be half black and half red, but we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling will reflect expected ratios.

Teaching Tips

Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses occurring simultaneously.

Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. We would expect that any six playing cards dealt might be half black and half red, but we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling will reflect expected ratios.

Teaching Tips

Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses occurring simultaneously.

Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. We would expect that any six playing cards dealt might be half black and half red, but we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling will reflect expected ratios.

Teaching Tips

Understanding dihybrid crosses may be the most difficult concept in this chapter. Consider spending additional time to make these ideas very clear. As the text indicates, dihybrid crosses are essentially two monohybrid crosses occurring simultaneously.

- 1. Chapter 9 Patterns of Inheritance PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko
- 2. Figure 9.0_1 Chapter 9: Big Ideas Mendel’s Laws The Chromosomal Basis of Inheritance
- 3. 9.2 Experimental genetics began in an abbey garden Heredity is the transmission of traits from one generation to the next. Genetics is the scientific study of heredity. Gregor Mendel • began the field of genetics in the 1860s, • discovered the principles of genetics by breeding garden peas © 2012 Pearson Education, Inc.
- 4. 9.2 A heritable feature that varies among individuals, such as flower color, is called a character. Each variant for a character, such as purple or white flowers, is a trait. © 2012 Pearson Education, Inc.
- 5. 9.2 True-breeding plants, after self-fertilization, produce offspring all identical to the parent. The offspring produced by two different true-breeding varieties are called hybrids. The cross-fertilization is called a genetic cross. © 2012 Pearson Education, Inc.
- 6. Figure 9.2C_s3 White 1 Removal of stamens Stamens Carpel Parents (P) 2 Transfer Purple of pollen 3 Carpel matures into pea pod 4 Seeds from pod planted Offspring (F1)
- 7. 9.3 Mendel’s law of segregation describes the inheritance of a single character A cross between two individuals differing in a single character is a monohybrid cross. Mendel performed a monohybrid cross between a plant with purple flowers and a plant with white flowers. © 2012 Pearson Education, Inc.
- 8. Figure 9.3A_s3 The Experiment P generation (true-breeding parents) × Purple flowers F1 generation White flowers All plants have purple flowers Fertilization among F1 plants (F1 × F1) F2 generation 3 4 1 of plants of plants 4 have purple flowers have white flowers
- 9. 9.3 Mendel developed four hypotheses: 1. Alleles are alternative versions of genes that account for variations in inherited characters. 2. For each characteristic, an organism inherits two alleles, one from each parent. The alleles can be the same or different. – A homozygous genotype has identical alleles. – A heterozygous genotype has two different alleles. © 2012 Pearson Education, Inc.
- 10. 9.3 3. Alleles are inherited in pairs. • A dominant allele is always expressed if present. • A recessive allele is expressed ONLY if both alleles are recessive. – The phenotype is the appearance or expression of a trait. – The genotype is the genetic makeup of a trait. – The same phenotype may be determined by more than one genotype. © 2012 Pearson Education, Inc.
- 11. 9.3 4. A sperm or egg carries only one allele for each inherited character • allele pairs separate (segregate) from each other during the production of gametes. • This statement is called the law of segregation. – A Punnett square shows the four possible combinations of alleles that could occur when these gametes combine. © 2012 Pearson Education, Inc.
- 12. Practice Problems For each genotype, indicate whether it is heterozygous or homozygous: 1. AA 2. Tt 3. aa 4. Yy 5. Rr
- 13. Practice Problems For each genotype determine the phenotype: 1. Aa 2. TT 3. Rr 4. Gg 5. pp
- 14. Practice Problems For each phenotypes write the possible genotypes: 1. Constricted pods 2. Tall plant 3. Round seeds 4. White flowers 5. Yellow seeds
- 15. 9.7 Mendel’s laws reflect the rules of probability Probability – the likelihood that a specific, random event will occur Probability predicts an average number of occurrences, not an exact number of occurrences. Probability = number of ways and event can occur total number of all possible outcomes The probability scale ranges from 0 to 1. An event that is – certain has a probability of 1 and – certain not to occur has a probability of 0. © 2012 Pearson Education, Inc.
- 16. Monohybrid Punnett Squares •The Punnett square yields the ratio of possible genotypes and phenotypes.
- 17. Figure 9.3B_s3 The Explanation P generation Genetic makeup (alleles) White flowers Purple flowers PP pp Gametes All P All p F1 generation (hybrids) All Pp Gametes 1 2 P Alleles segregate 1 2 p Fertilization Sperm from F1 plant F2 generation P Phenotypic ratio 3 purple : 1 white Genotypic ratio 1 PP : 2 Pp : 1 pp P Eggs from F1 plant p p PP Pp Pp pp
- 18. 25% or ¼ of the offspring have the homozygous dominant genotype (FF) 50% or 2/4 have the heterozygous genotype (Ff) 25% or ¼ have the homozygous recessive genotype (ff) – A genotypic ratio of 1:2:1 This results in 75% or ¾ offspring – FF : Ff : ff having purple flowers 25% or ¼ offspring having white flowers – A phenotypic ratio of 3:1 – Dominant : Recessive
- 19. Practice Problems Cross a pea plant that is heterozygous for yellow seed color with another pea plant that is also heterozygous for yellow seed color. What are the genotypic and phenotypic ratios?
- 20. 9.4 Homologous chromosomes bear the alleles for each character A locus (plural, loci) is the specific location of a gene along a chromosome. For a pair of homologous chromosomes, alleles of a gene are at the same locus. – Homozygous individuals have the same allele on both homologues. – Heterozygous individuals have a different allele on each homologue. © 2012 Pearson Education, Inc.
- 21. Figure 9.4 Gene loci P a B P a b Dominant allele Homologous chromosomes Genotype: PP Homozygous for the dominant allele aa Homozygous for the recessive allele Recessive allele Bb Heterozygous, with one dominant and one recessive allele
- 22. 9.16 Chromosome behavior accounts for Mendel’s laws Mendel’s laws correlate with chromosome separation in meiosis. – The law of segregation depends on separation of homologous chromosomes in anaphase I. – The law of independent assortment depends on alternative orientations of chromosomes in metaphase I. © 2012 Pearson Education, Inc.
- 23. Figure 9.16_s3 F1 generation R r All yellow round seeds (RrYy) y Y Y R r r R y Metaphase I of meiosis R Y y r r R Y y Anaphase I Y y R r Y Metaphase II R Y y r y Gametes Y Y R R 1 4 RY y Y r r 1 4 Y r y r ry F2 generation 9 Fertilization :3 :3 :1 1 4 rY y y R R 1 4 Ry
- 24. 9.5 The law of independent assortment is revealed by tracking two characters at once A dihybrid cross shows two different characters. © 2012 Pearson Education, Inc.
- 25. Dihybrid crosses Dihybrid crosses consider two pairs of contrasting traits. • In this example two plants, each heterozygous for Yellow and Round Seeds are crossed (YyRr). •The result is: •9/16 plants with yellow and round seeds. •3/16 plants with yellow and wrinkled seeds. •3/16 plants with green and round seeds. •1/16 plants with green and wrinkled seeds. •Phenotypic ratio of 9:3:3:1
- 26. Practice Problem If you cross a pea plant that is heterozygous for axial flowers and has green seeds, with a pea plant that has terminal flowers and is heterozygous for yellow seeds, what is the probability the offspring will have – axial flowers and yellow seeds? – Axial flowers and green seeds? – Terminal flowers and yellow seeds? – Terminal flowers and green seeds? What is the phenotypic ratio?
- 27. 9.5 Mendel suggested that the inheritance of one character has no effect on the inheritance of another. – He called this the law of independent assortment. © 2012 Pearson Education, Inc.
- 28. 9.5 The following figure demonstrates the law of independent assortment as it applies to two characters in Labrador retrievers: – black versus chocolate color, – normal vision versus progressive retinal atrophy. © 2012 Pearson Education, Inc.
- 29. Figure 9.5B Blind Blind Phenotypes Genotypes Black coat, normal vision B_N_ Black coat, blind (PRA) B_nn Chocolate coat, normal vision bbN_ Chocolate coat, blind (PRA) bbnn Mating of double heterozygotes (black coat, normal vision) BbNn BbNn × Blind Blind Phenotypic ratio of the offspring 9 Black coat, normal vision 3 Black coat, blind (PRA) 3 Chocolate coat, normal vision 1 Chocolate coat, blind (PRA)
- 30. You should now be able to 1. Define and distinguish between true-breeding organisms, hybrids, the P generation, the F1 generation, and the F2 generation. 2. Define and distinguish between the following pairs of terms: homozygous and heterozygous; dominant allele and recessive allele; genotype and phenotype. Also, define a monohybrid cross and a Punnett square. © 2012 Pearson Education, Inc.
- 31. You should now be able to 3. Explain how Mendel’s law of segregation describes the inheritance of a single characteristic. 4. Describe the genetic relationships between homologous chromosomes. 5. Explain how Mendel’s law of independent assortment applies to a dihybrid cross. 6. Define the chromosome theory of inheritance. Explain the chromosomal basis of the laws of segregation and independent assortment. © 2012 Pearson Education, Inc.

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