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# Chapter 9 part 2

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• Figure 9.0_1 Chapter 9: Big Ideas
• Student Misconceptions and Concerns
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.
• Figure 9.5B Independent assortment of two genes in the Labrador retriever
• Figure 9.5B_1 Independent assortment of two genes in the Labrador retriever (part 1)
• Figure 9.5B_2 Independent assortment of two genes in the Labrador retriever (part 2)
• Student Misconceptions and Concerns
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.
• Student Misconceptions and Concerns
Students might think that dominant alleles are naturally (a) more common, (b) more likely to be inherited, and (c) better for an organism. The text notes that this is not necessarily true. However, this might need to be emphasized further in lecture.
Teaching Tips
Students seem to learn much from Figure 9.8b by analyzing the possible genotypes for the people whose complete genotype is not known. Consider challenging your students to suggest the possible genotypes for these people, perhaps during lecture.
• Figure 9.8A Examples of single-gene inherited traits in humans
• Figure 9.8B A pedigree showing the inheritance of attached versus free earlobes in a hypothetical family
• Teaching Tips
1. The 2/3 fraction noted in the discussion of carriers of a recessive disorder for deafness often catches students off guard . . . as they are expecting odds of 1/4, 1/2, or 3/4. However, when we eliminate the dd (deaf) possibility, as it would not be a carrier, we have three possible genotypes. Thus, the odds are based out of the remaining three genotypes Dd, dD, and DD. Consider adding this point of clarification to your lecture.
2. As a simple test of comprehension, ask students to explain why lethal alleles are not eliminated from a population. Several possibilities exist: a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or b) the lethal allele might be dominant, but is not expressed until after the age of reproduction.
3. Ask your class a) what the odds are of a person developing Huntington’s disease if a parent has this disease (50%) and b) whether they would want this genetic test if they were a person at risk. The Huntington Disease Society website, www.hdsa.org, offers many additional details. It is a good starting point for those who want to explore this disease in more detail.
• Figure 9.9A Offspring produced by parents who are both carriers for a recessive disorder, a type of deafness
• Teaching Tips
1. The 2/3 fraction noted in the discussion of carriers of a recessive disorder for deafness often catches students off guard . . . as they are expecting odds of 1/4, 1/2, or 3/4. However, when we eliminate the dd (deaf) possibility, as it would not be a carrier, we have three possible genotypes. Thus, the odds are based out of the remaining three genotypes Dd, dD, and DD. Consider adding this point of clarification to your lecture.
2. As a simple test of comprehension, ask students to explain why lethal alleles are not eliminated from a population. Several possibilities exist: a) The lethal allele might be recessive, persisting in the population due to the survival of carriers, or b) the lethal allele might be dominant, but is not expressed until after the age of reproduction.
3. Ask your class a) what the odds are of a person developing Huntington’s disease if a parent has this disease (50%) and b) whether they would want this genetic test if they were a person at risk. The Huntington Disease Society website, www.hdsa.org, offers many additional details. It is a good starting point for those who want to explore this disease in more detail.
• Table 9.9 Some Autosomal Disorders in Humans
• Teaching Tips
Medical technology raises many ethical issues. Consider asking your students this practical question. How much routine fetal testing do we want our insurance companies to cover and at what cost for health insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay?
• Teaching Tips
Medical technology raises many ethical issues. Consider asking your students this practical question. How much routine fetal testing do we want our insurance companies to cover and at what cost for health insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay?
• Figure 9.10A Testing a fetus for genetic disorders
• Teaching Tips
Medical technology raises many ethical issues. Consider asking your students this practical question. How much routine fetal testing do we want our insurance companies to cover and at what cost for health insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay?
• Figure 9.10B Ultrasound scanning of a fetus
• Teaching Tips
Medical technology raises many ethical issues. Consider asking your students this practical question. How much routine fetal testing do we want our insurance companies to cover and at what cost for health insurance? Ultrasound, for example, is routinely performed on pregnant women as a normal part of prenatal care. What other tests should be standard? Who should decide? Who should pay?
• Student Misconceptions and Concerns
1. After reading the preceding modules, students might expect all traits to be governed by a single gene with two alleles, one dominant over the other. Modules 9.11–9.15 describe deviations from simplistic models of inheritance.
2. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference).
3. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class.
Teaching Tips
1. Students can think of blood types as analogous to socks on their feet. You can have socks that match, a sock on one foot but not the other, you can wear two socks that do not match, or you can even go barefoot (type O blood)! Developed further, think of Amber (A) and Blue (B) socks. Type A blood can have an Amber sock with either another Amber sock or a bare foot (or “zero” sock). Blue socks work the same way. One amber and one blue sock represent the AB blood type. No socks, as already noted, represent type O.
2. Consider specifically comparing the principles of codominance (expression of both alleles) and incomplete dominance (expression of one intermediate trait). Students will likely benefit from this direct comparison.
• Student Misconceptions and Concerns
1. After reading the preceding modules, students might expect all traits to be governed by a single gene with two alleles, one dominant over the other. Modules 9.11–9.15 describe deviations from simplistic models of inheritance.
2. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference).
3. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class.
Teaching Tips
1. Students can think of blood types as analogous to socks on their feet. You can have socks that match, a sock on one foot but not the other, you can wear two socks that do not match, or you can even go barefoot (type O blood)! Developed further, think of Amber (A) and Blue (B) socks. Type A blood can have an Amber sock with either another Amber sock or a bare foot (or “zero” sock). Blue socks work the same way. One amber and one blue sock represent the AB blood type. No socks, as already noted, represent type O.
2. Consider specifically comparing the principles of codominance (expression of both alleles) and incomplete dominance (expression of one intermediate trait). Students will likely benefit from this direct comparison.
• Figure 9.12 Multiple alleles for the ABO blood groups
• Student Misconceptions and Concerns
1. After reading the preceding modules, students might expect all traits to be governed by a single gene with two alleles, one dominant over the other. Modules 9.11–9.15 describe deviations from simplistic models of inheritance.
2. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference).
3. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class.
Teaching Tips
1. Polygenic inheritance makes it possible for children to inherit genes to be taller or shorter than either parent. Similarly, skin tones can be darker or lighter than either parent. The environment also contributes significantly to the final phenotype for both of these traits.
2. The authors note that polygenic inheritance is the converse of pleiotropy. This is worth noting in lecture as these concepts are discussed. We often remember concepts better when they are contrasted in pairs.
• Figure 9.14_1 A model for polygenic inheritance of skin color (part 1)
• Figure 9.14_2 A model for polygenic inheritance of skin color (part 2)
• Figure 9.14_3 A model for polygenic inheritance of skin color (part 3)
• Student Misconceptions and Concerns
1. After reading the preceding modules, students might expect all traits to be governed by a single gene with two alleles, one dominant over the other. Modules 9.11–9.15 describe deviations from simplistic models of inheritance.
2. As these variations of Mendel’s laws are introduced, students are likely to get confused and become uncertain about the prior definitions. Consider keeping a clear definition of these different patterns of inheritance available for the class to refer to as new patterns are discussed (perhaps as a handout for student reference).
3. As your class size increases, the chances increase that at least one student will have a family member with one of the genetic disorders discussed. Some students may find this embarrassing, but others might have a special interest in learning more about these topics, and may even be willing to share some of their family’s experiences with the class.
Teaching Tips
1. The authors note that polygenic inheritance is the converse of pleiotropy. This is worth noting in lecture as these concepts are discussed. We often remember concepts better when they are contrasted in pairs.
2. As the authors are careful to note, although genetics and the environment both contribute to the final phenotypes, only the genetic factors are inherited. This distinction is important to understanding the limitations of Lamarck’s mechanisms of evolution. If you will address principles of evolution soon after this chapter, this may be an important distinction to reinforce in lecture. References to tattoos and piercing may also help to distinguish between environmental influences and inheritance. Students with tattoos will not produce children born with tattoos!
• ### Chapter 9 part 2

1. 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. 2. Figure 9.0_1 Chapter 9: Big Ideas Mendel’s Laws The Chromosomal Basis of Inheritance Variations on Mendel’s Laws Sex Chromosomes and Sex-Linked Genes
3. 3. 9.5 The law of independent assortment is revealed by tracking two characters at once  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.
4. 4. 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)
5. 5. Figure 9.5B_1 Blind Phenotypes Genotypes Black coat, normal vision B_N_ Black coat, blind (PRA) B_nn Blind Phenotypes Genotypes Chocolate coat, normal vision bbN_ Chocolate coat, blind (PRA) bbnn
6. 6. Figure 9.5B_2 Mating of double heterozygotes (black coat, normal vision) BbNn × BbNn Blind Phenotypic ratio of the offspring 9 Black coat, normal vision Blind 1 3 3 Black coat, Chocolate coat, Chocolate coat, blind (PRA) blind (PRA) normal vision
7. 7. 9.7 Mendel’s laws reflect the rules of probability  Using his strong background in mathematics, Mendel knew that the rules of mathematical probability affected – the segregation of allele pairs during gamete formation and – the re-forming of pairs at fertilization.  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.
8. 8. Evaluating Results  Mendel was unable to analyze mathematically how well the actual outcome of his crosses fulfilled his predictions. – Karl Pearson developed the chi-square (χ2) test – Determines whether the observed distribution of individuals in as predicted or occurs by chance. – If there is no difference between the observed and expected classes the value for χ2 will be 0. – The value of χ2 increases with greater difference between the observed and expected classes. – The formula can be expressed as χ2 = Σ (O-E)2 ÷ E – O is # observed and E is # expected
9. 9. We must now convert χ2 into probability in order to determine if the χ2 value is expected.  df (degrees of freedom) = number of classes – 1  We can then use the table below to determine whether the data collected is acceptable. – A p value of less than 0.05 means that the observations do not meet the expected outcome and needs to be reexamined
10. 10. 9.8 Genetic traits in humans can be tracked through family pedigrees  The inheritance of human traits follows Mendel’s laws.  A pedigree – shows the inheritance of a trait in a family through multiple generations, – demonstrates dominant or recessive inheritance, and – can also be used to deduce genotypes of family members. © 2012 Pearson Education, Inc.
11. 11. Figure 9.8A Dominant Traits Recessive Traits Freckles No freckles Widow’s peak Straight hairline Free earlobe Attached earlobe
12. 12. Figure 9.8B First generation (grandparents) Second generation (parents, aunts, FF and uncles) or Ff Third generation (two sisters) Female Male Attached Free Ff ff Ff ff ff Ff Ff Ff ff ff FF or Ff
13. 13. 9.9 Many inherited disorders in humans are controlled by a single gene  Inherited human disorders show either 1. recessive inheritance in which – two recessive alleles are needed to show disease – heterozygous parents are carriers of the disease-causing allele – the probability of inheritance increases with inbreeding, mating between close relatives 1. dominant inheritance in which – one dominant allele is needed to show disease and – dominant lethal alleles are usually eliminated from the population. © 2012 Pearson Education, Inc.
14. 14. Figure 9.9A Normal Dd Parents D D Offspring Normal Dd × Sperm d DD Normal Dd Normal (carrier) Dd Normal (carrier) dd Deaf Eggs d
15. 15. 9.9  The most common fatal genetic disease in the United States is cystic fibrosis (CF), resulting in excessive thick mucus secretions. The CF allele is – recessive and – carried by about 1 in 31 Americans.  Dominant human disorders include – achondroplasia, resulting in dwarfism, and – Huntington’s disease, a degenerative disorder of the nervous system. © 2012 Pearson Education, Inc.
16. 16. Table 9.9
17. 17. 9.10 New technologies can provide insight into one’s genetic legacy  New technologies offer ways to obtain genetic information – before conception, – during pregnancy, and – after birth.  Genetic testing can identify potential parents who are heterozygous carriers for certain diseases. © 2012 Pearson Education, Inc.
18. 18. 9.10 New technologies can provide insight into one’s genetic legacy  Several technologies can be used for detecting genetic conditions in a fetus. – Amniocentesis extracts samples of amniotic fluid containing fetal cells – Usually performed in the sixteenth week of pregnancy – Chorionic villus sampling removes a sample of chorionic villus tissue from the placenta and permits similar karyotyping and biochemical tests. – Usually performed in the eighth or ninth week of pregnancy © 2012 Pearson Education, Inc.
19. 19. Figure 9.10A Amniocentesis Chorionic Villus Sampling (CVS) Amniotic fluid extracted Ultrasound transducer Fetus Ultrasound transducer Fetus Placenta Chorionic villi Placenta Uterus Cervix Centrifugation Amniotic fluid Fetal cells Several hours Cultured cells Tissue extracted from the chorionic villi Several weeks Several weeks Karyotyping Biochemical and genetics tests Cervix Uterus Fetal cells Several hours Several hours
20. 20. 9.10  Blood tests on the mother at 14–20 weeks of pregnancy can help identify fetuses at risk for certain birth defects (neural tube defects and Down syndrome).  Fetal imaging enables a physician to examine a fetus directly for anatomical deformities. The most common procedure is ultrasound imaging, using sound waves to produce a picture of the fetus.  Newborn screening can detect diseases that can be prevented by special care and precautions.  PKU © 2012 Pearson Education, Inc.
21. 21. Figure 9.10B
22. 22. 9.10  New technologies raise ethical considerations that include – the confidentiality and potential use of results of genetic testing, – time and financial costs, and – determining what, if anything, should be done as a result of the testing. © 2012 Pearson Education, Inc.
23. 23. 9.12 Many genes have more than two alleles in the population  Although an individual can at most carry two different alleles for a particular gene, more than two alleles often exist in the wider population.  Human ABO blood group phenotypes involve three alleles for a single gene.  The four human blood groups, A, B, AB, and O, result from combinations of these three alleles.  The A and B alleles are both expressed in heterozygous individuals, a condition known as codominance. © 2012 Pearson Education, Inc.
24. 24. 9.12 Many genes have more than two alleles in the population  In codominance, – neither allele is dominant over the other and – expression of both alleles is observed as a distinct phenotype in the heterozygous individual. – AB blood type is an example of codominance. © 2012 Pearson Education, Inc.
25. 25. Figure 9.12 Blood Group (Phenotype) Genotypes Carbohydrates Present on Red Blood Cells A IAIA or IAi Carbohydrate A Reaction When Blood from Groups Below Is Mixed with Antibodies from Groups at Left O A B AB Carbohydrate B B IBIB or IBi Antibodies Present in Blood AB O IAIB ii Anti-B Anti-A Carbohydrate A and Carbohydrate B Neither None Anti-A Anti-B No reaction Clumping reaction
26. 26. 9.14 A single character may be influenced by many genes  Many characteristics result from polygenic inheritance, in which a single phenotypic character results from the additive effects of two or more genes.  Human skin color is an example of polygenic inheritance. © 2012 Pearson Education, Inc.
27. 27. Figure 9.14_1 P generation × aabbcc AABBCC (very light) (very dark) F1 generation × AaBbCc AaBbCc
28. 28. Figure 9.14_2 Sperm F2 generation 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 Eggs 1 8 1 8 1 8 1 8 1 8 1 64 6 64 15 64 20 64 15 64 6 64 1 64
29. 29. Figure 9.14_3 Fraction of population 20 64 15 64 6 64 1 64 Skin color
30. 30. 9.15 The environment affects many characters  Many characters result from a combination of heredity and the environment.  skin color is affected by exposure to sunlight  susceptibility to diseases, such as cancer, has hereditary and environmental components  identical twins show some differences  Complex traits are determined by the cumulative effects of genes and the influence of environment  Examples: Skin color and IQ  Only genetic influences are inherited. © 2012 Pearson Education, Inc.
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