1. LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick Mendel and the Gene Idea Chapter 14

3. Figure 14.1

4. Gregor Mendel “FATHER OF GENETICS” An Austrian monk His work was important to the understanding of heredity Carried out quantitative work with ordinary garden peas

5. Concept 14.1: Mendel used the scientific approach to identify two laws of inheritance Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments © 2011 Pearson Education, Inc.

6. Mendel’s Experimental, Quantitative Approach Advantages of pea plants for genetic study –There are many varieties with distinct heritable features, or traits –Mating can be controlled –Each flower is perfect has sperm-producing organs (stamens) and an egg-producing organ (carpel) –Cross-pollination relatively simple © 2011 Pearson Education, Inc.

7. Genes and Dominance TRAIT: specific characteristic (color or height) that varies from one individual to another Mendel studied SEVEN different traits

8. Table 14.1

9. In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization In this example, the true-breeding parents are the P generation The hybrid offspring of the P generation are called the F 1 generation When F 1 individuals self-pollinate or cross- pollinate with other F 1 hybrids, the F 2 generation is produced © 2011 Pearson Education, Inc.

10. Figure 14.3-1 P Generation EXPERIMENT: Law of Segregation (true-breeding parents) Purple flowers White flowers

11. Figure 14.3-2 P Generation EXPERIMENT (true-breeding parents) F 1 Generation (hybrids) Purple flowers White flowers All plants had purple flowers Self- or cross-pollination EXPERIMENT: Law of Segregation

12. Figure 14.3-3 P Generation EXPERIMENT (true-breeding parents) F 1 Generation (hybrids) F 2 Generation Purple flowers White flowers All plants had purple flowers Self- or cross-pollination 705 purple- flowered plants 224 white flowered plants EXPERIMENT: Law of Segregation

13. Did the recessive alleles disappear? P Generation F 1 Generation Tall Short F 2 Generation Mendel crossed F 1 generation with itself and traits controlled by recessive alleles reappeared in the F 2 generation!!

14. Mendel’s Model (His 4 Main Ideas) Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F 2 offspring Four related concepts make up this model These concepts can be related to what we now know about genes and chromosomes © 2011 Pearson Education, Inc.

15. First: alternative versions of genes account for variations in inherited characters –Ex: gene for flower color in pea plants exists in two versions, one for purple flowers and the other for white flowers These alternative versions of a gene are now called alleles Each gene resides at a specific locus on a specific chromosome © 2011 Pearson Education, Inc. Allele for purple flowers Locus for flower-color gene Allele for white flowers Pair of homologous chromosomes

16. Second: for each character, an organism inherits two alleles, one from each parent –Mendel made this deduction without knowing about the role of chromosomes The two alleles at a particular locus may be identical, as in the true-breeding plants of Mendel’s P generation, or they may differ © 2011 Pearson Education, Inc.

17. Third: if the two alleles at a locus differ, then one (the dominant allele) determines the organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance In the flower-color example, the F 1 plants had purple flowers because the allele for that trait is dominant © 2011 Pearson Education, Inc.

18. Fourth (now known as the law of segregation): the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes –Thus, an egg or a sperm gets only one of the two alleles that are present in the organism © 2011 Pearson Education, Inc.

19. Law of Segregation States that allele pairs separate during gamete formation and randomly reunite at fertilization Person with a dominant and recessive produces two types of gametes because they separate! Person with a both alleles the same produces one type of gamete even though they separate!

20. Phenotype Purple White 3 1 1 1 2 Ratio 3:1 Ratio 1:2:1 Genotype PP (homozygous) Pp (heterozygous) pp (homozygous) Figure 14.6

21. How to discover genotype of unknown flower How can we tell the genotype of an individual with the dominant phenotype?

22. The Testcross How can we tell the genotype of an individual with the dominant phenotype? Carry out a testcross: breeding the mystery individual with a homozygous recessive individual If any offspring display the recessive phenotype, the mystery parent must be heterozygous © 2011 Pearson Education, Inc.

23. The testcross Figure 14.7  Dominant phenotype, unknown genotype: PP or Pp? Recessive phenotype, known genotype: pp If PP, then all offspring purple: If Pp, then 1 ⁄ 2 offspring purple and 1 ⁄ 2 offspring white: p p P P Pp pp Pp P p pp APPLICATION An organism that exhibits a dominant trait, such as purple flowers in pea plants, can be either homozygous for the dominant allele or heterozygous. To determine the organism’s genotype, geneticists can perform a testcross. TECHNIQUE In a testcross, the individual with the unknown genotype is crossed with a homozygous individual expressing the recessive trait (white flowers in this example). By observing the phenotypes of the offspring resulting from this cross, we can deduce the genotype of the purple-flowered parent. RESULTS

24. Probability Likelihood that a particular event will occur PRINCIPLES OF PROBABILITY CAN BE USED TO PREDICT THE OUTCOME OF GENETIC CROSSES… MENDEL WAS ALWAYS ABLE TO PREDICT WHAT HIS RESULTS SHOULD ROUGHLY BE!!

25. Figure 14.9 Segregation of alleles into eggs Segregation of alleles into sperm Sperm Eggs 1/21/2 1/21/2 1/21/2 1/21/2 1/41/4 1/41/4 1/41/4 1/41/4 Rr R R R R R R r r r r r  r

26. Figure 14.UN01 Probability of YYRR Probability of YyRR 1 / 4 (probability of YY) 1 / 2 (Yy) 1 / 4 (RR) 1 / 16 1/81/8      

27. Figure 14.UN02 Chance of at least two recessive traits ppyyRr ppYyrr Ppyyrr PPyyrr ppyyrr 1 / 4 (probability of pp)  1 / 2 (yy)  1 / 2 (Rr) 1/4  1/2  1/21/4  1/2  1/2 1/2  1/2  1/21/2  1/2  1/2 1/4  1/2  1/21/4  1/2  1/2 1/4  1/2  1/21/4  1/2  1/2  1 / 16  2 / 16  1 / 16  6 / 16 or 3 / 8

28. Punnett Squares Diagram used to show the gene combinations that might result from a genetic cross Parent alleles shown on the TOP and LEFT… Letters are used to represent different ALLELES CAPITAL letters = DOMINANT alleles lowercase letters = recessive alleles POSSIBLE gene combinations of the offspring appear in the four boxes RR r r

29. Punnett Squares HOMOZYGOUS  Two identical alleles for a particular trait EX: TT, tt, BB, bb, etc.(TRUE BREEDING) HETEROZYGOUS  Two different alleles for a trait EX: Tt, Bb, etc.(HYBRID) ALLELES OF GENES: OUTCOMES: PHENOTYPE  physical characteristics or what you see in the offspring of a cross GENOTYPE  genetic makeup or what combinations of alleles form from a cross

30. Punnett Squares TT T t 1) Always use a trait KEY to indicate what the letters you are using stand for 2) Determine the genotypes of the parents from the problem 3) Offspring can be predicted by doing the cross and filling in the boxes! 4) List PHENOTYPIC ratio ____:____:____ T T t T = Tall t = Short 100% Tall 50% TT 50% Tt Choose letters that look different upper / lowercase

31. Monohybrid Crosses Crosses involving only ONE gene In sheep: The allele for white wool (A) is dominant The allele for black wool (a) A homozygous recessive mates with a heterozygous. Phenotypes/genotypes of the offspring? A = White a = Black a a aA A aa A a a 50% White 50% Black 50% Aa 50% aa

32. Monohybrid Crosses Practice In guinea pigs, the allele for rough coat is dominant over the allele for smooth coat. Cross a hybrid guinea pig with a homozygous rough coated individual. (Show the key, Punnett square, and phenotypes / genotypes)

33. Monohybrid Crosses Practice In tomato plants, red fruit is dominant over yellow fruit. A homozygous dominant plant is crossed with a true breeding red fruited plant. What is the chance that a yellow fruited tomato plant will form? (Show the key, Punnett square, and phenotypes / genotypes)

34. Monohybrid Crosses Practice In humans, being a tongue roller is dominant over non- roller. A man who is a non-roller marries a woman who is homozygous for tongue rolling. (Show the key, Punnett square, and phenotypes / genotypes)

35. Law of Independent Assortment States that genes for different traits can segregate (separate) independently during the formation of gametes Mendel discovered this after doing a dihybrid cross (homozygous dominant round yellow with homozygous recessive wrinkled green) and then crossing the offspring (heterozygous for both traits)

36. Law of Independent Assortment Helps account for the many genetic variations observed in plants, animals, and other organisms!

37. Dihybrid Crosses Chalkboard practice cross Two heterozygous round, yellow pea plants are crossed. 1.Determine parent genotype 2.Determine possible gametes using FOIL method 3.Complete Punnett square, showing work 4.Write out phenotypic ratio

38. Summary of Mendel’s Ideas Genes are passed from parents to their offspring If two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive (Law of Dominance) In most organisms, each adult has two copies of each gene and these genes are segregated from each other when gametes are formed (Law of Segregation) Alleles for different genes usually segregate independently of one another (Law of Independent Assortment) Even though Mendel is right, there are SOME exceptions to his principles…

39. Make A Baby Choose a partner Materials: –Lab packet (DO NOT WRITE ON IT) –2 pennies –Lab notebook –Paper –Colored pencils, crayons, or markers

41. Extending Mendelian Genetics for a Single Gene Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations: –When alleles are not completely dominant or recessive –When a gene has more than two alleles –When a gene produces multiple phenotypes © 2011 Pearson Education, Inc.

42. Degrees of Dominance Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical In incomplete dominance, the phenotype of F 1 hybrids is somewhere between the phenotypes of the two homozygous parents (blending) In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways © 2011 Pearson Education, Inc.

43. Figure 14.10-1 P Generation Red White Gametes CWCWCWCW CRCRCRCR CRCR CWCW Incomplete Dominance

44. Figure 14.10-2 P Generation F 1 Generation 1/21/2 1/21/2 Red White Gametes Pink Gametes CWCWCWCW CRCRCRCR CRCR CWCW CRCWCRCW CRCR CWCW Incomplete Dominance

45. Figure 14.10-3 P Generation F 1 Generation F 2 Generation 1/21/2 1/21/2 1/21/2 1/21/2 1/21/2 1/21/2 Red White Gametes Pink Gametes Sperm Eggs CWCWCWCW CRCRCRCR CRCR CWCW CRCWCRCW CRCR CWCW CWCW CRCR CRCR CWCW CRCRCRCR CRCWCRCW CRCWCRCW CWCWCWCW Incomplete Dominance

46. Incomplete Dominance When doing crosses for these problems, you MUST include the intermediate in your key and TWO different letters can be used for the dominant and recessive alleles (don’t have to)… Otherwise, the problems are the same as a monohybrid cross. C R C R = Red C R C W = Pink C W C W = White

47. Incomplete Dominance A small bird species has a gene that determines beak size. In these birds, large beaks help crush big seeds, small beaks are used to pick seeds from pine cones, and intermediate beaks help consume both types of seeds. Cross a large beaked bird with an intermediate beaked bird. What will the offspring look like?

48. Incomplete Dominance The lubber grasshopper is a large grasshopper that can have yellow and red stripes. Assume red stripes are expressed from the homozygous S R S R genotype, yellow stripes from the S y S y genotype, and both from the heterozygous genotype. Cross two heterozygous grasshoppers and predict their offspring.

49. Codominance Both alleles contribute to the phenotype or both can be seen at the same time (NOT a blending) Ex: In certain varieties of chicken, the allele for black feathers is codominant with the allele for white feathers… Heterozygous chickens have BOTH black and white feathers!

50. Roan cattle/horse: Codominance

51. Multiple Alleles Many genes have more than two alleles in a population (each individual only has two alleles, but more exist) EX: Rabbit coat color is determined by a gene that has at least four different alleles KEY C = full color; dominant to all other alleles c ch = chinchilla; partial defect in pigmentation; dominant to c h and c alleles c h = Himalayan; color in certain parts of the body; dominant to c allele c = albino; no color; recessive to all other alleles

52. Multiple Alleles Most genes exist in populations in more than two allelic forms For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: I A, I B, and i. The enzyme encoded by the I A allele adds the A carbohydrate, whereas the enzyme encoded by the I B allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither © 2011 Pearson Education, Inc.

53. Blood Group Genes Blood genes are a mix of codominance and multiple alleles Humans can have A, B, AB, or O blood type Multiple Alleles (3 of them)  I A, I B, or i / A, B, O Codominance  I A and I B are codominant

54. Figure 14.11 Carbohydrate Allele (a) The three alleles for the ABO blood groups and their carbohydrates (b) Blood group genotypes and phenotypes Genotype Red blood cell appearance Phenotype (blood group) A A B B AB none O IAIA IBIB i ii IAIBIAIB I A I A or I A i I B I B or I B i

55. Blood Group Genes Blood TypeGenotypeAntigen on RBC Safe Transfusions ToFrom AI A I A or I A i AA or AO AA, ABA, O BI B I B or I B i BB or BO BB, ABB, O ABI A I B AB A and BABA, B, AB, O Oii OO NoneA, B, AB, OO When transfusing blood, a person’s blood type MUST be known and only certain types can be given… WHY? What blood type is the UNIVERSAL DONOR? What blood type is the UNIVERSAL ACCEPTOR?

56. Blood Group Genes A woman is homozygous for type A blood and a man has type AB blood. What is the probability that the couple’s child will have type B blood? Two individuals with type AB blood have a child. What are the chances that their child will have type O blood? A man with type O blood marries a woman who is heterozygous type A blood. What would be the blood type possibilities of their offspring?

58. Pleiotropy Most genes have multiple phenotypic effects, a property called pleiotropy For example, pleiotropic alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease © 2011 Pearson Education, Inc.

59. Extending Mendelian Genetics for Two or More Genes Some traits may be determined by two or more genes © 2011 Pearson Education, Inc.

60. Epistasis In epistasis, a gene at one locus alters the phenotypic expression of a gene at a second locus For example, in Labrador retrievers and many other mammals, coat color depends on two genes One gene determines the pigment color (with alleles B for black and b for brown) The other gene (with alleles C for color and c for no color) determines whether the pigment will be deposited in the hair © 2011 Pearson Education, Inc.

61. Figure 14.12 Sperm Eggs 9 : 3 : 4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 BbEe BE bE Be be BBEE BbEE BBEeBbEe BbEE bbEEBbEe bbEe BBEe BbEe BBeeBbee BbEebbEe Bbee bbee

62. Polygenic Inheritance Quantitative characters are those that vary in the population along a continuum Quantitative variation usually indicates polygenic inheritance, an additive effect of two or more genes on a single phenotype Skin color in humans is an example of polygenic inheritance © 2011 Pearson Education, Inc.

63. Figure 14.13 Eggs Sperm Phenotypes: Number of dark-skin alleles: 0 12345 6 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1 / 64 6 / 64 15 / 64 20 / 64 15 / 64 6 / 64 1 / 64 AaBbCc

64. Nature and Nurture: The Environmental Impact on Phenotype Another departure from Mendelian genetics arises when the phenotype for a character depends on environment as well as genotype The norm of reaction is the phenotypic range of a genotype influenced by the environment For example, hydrangea flowers of the same genotype range from blue-violet to pink, depending on soil acidity © 2011 Pearson Education, Inc.

65. Figure 14.14

66. Norms of reaction are generally broadest for polygenic characters Such characters are called multifactorial because genetic and environmental factors collectively influence phenotype © 2011 Pearson Education, Inc.

67. Concept 14.4: Many human traits follow Mendelian patterns of inheritance Humans are not good subjects for genetic research –Generation time is too long –Parents produce relatively few offspring –Breeding experiments are unacceptable However, basic Mendelian genetics endures as the foundation of human genetics © 2011 Pearson Education, Inc.

68. How Is Sex Determined? All human eggs cells carry a single X chromosome, while half of the sperm cells carry an X and the other half carry a Y chromosome! 50 / 50 CHANCE!

69. Sex-Linked Genes Genes located on the sex chromosomes Y chromosome is much smaller than the X chromosome and appears to contain only a few genes! Why are SEX-LINKED disorders more common in males than females?

70. Sex-Linked Genes Females have TWO X chromosomes, thus there must be two copies of a recessive allele for it to be expressed! Males have only ONE X chromosome, so only one copy of a recessive allele causes the expression! EX: Male colorblindness (1 : 10) results when a defective version of the gene is present, while female colorblindness (1 : 100) only results when two defective versions are present!

72. Sex-Linked Cross Similar to other crosses we have done… just remember that the SEX of the individual is important and that males only need ONE recessive allele to have a trait!

73. Sex-Linked Cross Two important genes on the X chromosome help control blood clotting. A person who has HEMOPHILIA is lacking a protein necessary for normal blood clotting. About 1 : 10,000 males is born with the disease and this can be treated with protein injections. People with this disease can bleed to death from minor cuts or may suffer internal bleeding! Cross a carrier mother with a man who has hemophilia. What are the chances of having a daughter with the disease? Two important genes on the X chromosome help control blood clotting. A person who has HEMOPHILIA is lacking a protein necessary for normal blood clotting. About 1 : 10,000 males is born with the disease and this can be treated with protein injections. People with this disease can bleed to death from minor cuts or may suffer internal bleeding! Cross a carrier mother with a man who has hemophilia. What are the chances of having a daughter with the disease?

74. Sex-Linked Cross In the U.S., one out of 3,000 males is born with Duchenne Muscular Dystrophy, a disorder that results in the weakening and loss of skeletal muscle. This is caused by a defective muscle protein. Cross a normal male with a carrier female. What are the chances that the couple will have a child with the disease? What are the chances that dad will give the disease to a son? In the U.S., one out of 3,000 males is born with Duchenne Muscular Dystrophy, a disorder that results in the weakening and loss of skeletal muscle. This is caused by a defective muscle protein. Cross a normal male with a carrier female. What are the chances that the couple will have a child with the disease? What are the chances that dad will give the disease to a son?

75. X-Chromosome Inactivation To adjust to the extra X chromosome in females, one X chromosome is RANDOMLY switched off to become a Barr body (dense region by nuclear envelope) WHY does this female cat have multiple, random colors being expressed?

76. Pedigree Analysis A pedigree is a family tree that describes the interrelationships of parents and children across generations Inheritance patterns of particular traits can be traced and described using pedigrees © 2011 Pearson Education, Inc.

77. Pedigree Charts Shows the relationships within a family and indicates the genotypes for a certain trait A circle represents a female. A horizontal line connecting a male and a female represents a marriage. A shaded circle or square indicates that a person expresses the trait. A square represents a male. A vertical line and a bracket connect the parents to their children. A circle or square that is not shaded indicates that a person does not express the trait. Half filled circle or square represents a carrier!

78. Figure 14.15 Key Male Female Affected male Affected female Mating Offspring 1st generation 2nd generation 3rd generation 1st generation 2nd generation 3rd generation Is a widow’s peak a dominant or recessive trait? (a)Is an attached earlobe a dominant or recessive trait? b) Widow’s peak No widow’s peak Attached earlobe Free earlobe FF or Ff WW or Ww Ww ww Ww ww Ff ff FF or Ff ff

79. Pedigrees can also be used to make predictions about future offspring We can use the multiplication and addition rules to predict the probability of specific phenotypes © 2011 Pearson Education, Inc.

80. Tay-Sachs disease is fatal; a dysfunctional enzyme causes an accumulation of lipids in the brain –At the organismal level, the allele is recessive –At the biochemical level, the phenotype (i.e., the enzyme activity level) is incompletely dominant –At the molecular level, the alleles are codominant © 2011 Pearson Education, Inc.

81. Frequency of Dominant Alleles Dominant alleles are not necessarily more common in populations than recessive alleles For example, one baby out of 400 in the United States is born with extra fingers or toes –Polydactyl The allele for this unusual trait is dominant to the allele for the more common trait of five digits per appendage In this example, the recessive allele is far more prevalent than the population’s dominant allele © 2011 Pearson Education, Inc.

82. Recessively Inherited Disorders Many genetic disorders are inherited in a recessive manner These range from relatively mild to life- threatening © 2011 Pearson Education, Inc.

83. The Behavior of Recessive Alleles Recessively inherited disorders show up only in individuals homozygous for the allele Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal; most individuals with recessive disorders are born to carrier parents Albinism is a recessive condition characterized by a lack of pigmentation in skin and hair © 2011 Pearson Education, Inc.

84. Figure 14.16 Parents Normal Aa Sperm Eggs Normal Aa AA Normal Aa Normal (carrier) Aa Normal (carrier) aa Albino A A a a

85. If a recessive allele that causes a disease is rare, then the chance of two carriers meeting and mating is low Consanguineous matings (i.e., matings between close relatives) increase the chance of mating between two carriers of the same rare allele Most societies and cultures have laws or taboos against marriages between close relatives © 2011 Pearson Education, Inc.

86. Common Human Disorders HUMAN GENOME PROJECT  Goal was to map the entire sequence of human genes… completed in 2003!

87. Common Human Disorders CYSTIC FIBROSIS Missing three bases… Phenylalanine is missing Normal CFTR allows Cl - ions to pass… In CF, CFTR folded wrong and does not get put in membrane Cells cannot transport Cl - ions, airways clogged with mucus

88. Cystic Fibrosis Cystic fibrosis is the most common lethal genetic disease in the United States,striking one out of every 2,500 people of European descent The cystic fibrosis allele results in defective or absent chloride transport channels in plasma membranes leading to a buildup of chloride ions outside the cell Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine © 2011 Pearson Education, Inc.

89. Common Human Disorders SICKLE CELL Characterized by bent and twisted shape of red blood cells In normal cells, HEMOGLOBIN is the protein that carries oxygen In sickle cell, one base is changed, causing abnormal hemoglobin… during low levels of oxygen, some RBC become sickle shaped and can stick together!

90. Common Human Disorders SICKLE CELL

91. Common Human Disorders SICKLE CELL Why do so many African Americans carry the sickle cell allele? MALARIA  Disease that infects RBC and common in Africa.... Individuals HETEROZYGOUS for the disease are also RESISTANT to malaria. Low oxygen levels cause some RBC to become sickle shaped… body destroys these cells AND the parasite in the process! BEING HETEROZYGOUS FOR THE DISEASE IS ACTUALLY BENEFICIAL!!!!!

92. SICKLE CELL Why do so many African Americans carry the sickle cell allele? Common Human Disorders Regions where malaria is common Regions where the sickle cell allele is common

93. Sickle-Cell Disease: A Genetic Disorder with Evolutionary Implications Sickle-cell disease affects one out of 400 African-Americans The disease is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells In homozygous individuals, all hemoglobin is abnormal (sickle-cell) Symptoms include physical weakness, pain, organ damage, and even paralysis © 2011 Pearson Education, Inc.

94. Fig. 14-UN1 © 2011 Pearson Education, Inc. Heterozygotes (said to have sickle-cell trait) are usually healthy but may suffer some symptoms About one out of ten African Americans has sickle cell trait, an unusually high frequency of an allele with detrimental effects in homozygotes Heterozygotes are less susceptible to the malaria parasite, so there is an advantage to being heterozygous

95. Common Human Disorders NONDISJUNCTION  Failure of homologous chromosomes to separate during meiosis (abnormal #s of chromosomes can result) EXAMPLES -Down Syndrome (three copies of chromosome 21) aka “Trisomy 21” -Turner’s Syndrome (only one X chromosome)  Sterile -Klinefelter’s Syndrome (extra X in males, XXY)  Sterile

96. Dominantly Inherited Disorders Some human disorders are caused by dominant alleles Dominant alleles that cause a lethal disease are rare and arise by mutation Achondroplasia is a form of dwarfism caused by a rare dominant allele © 2011 Pearson Education, Inc.

97. Figure 14.17 Parents Dwarf Dd Sperm Eggs Dd Dwarf dd Normal Dd Dwarf dd Normal D d d d Normal dd

98. The timing of onset of a disease significantly affects its inheritance Huntington’s disease is a degenerative disease of the nervous system The disease has no obvious phenotypic effects until the individual is about 35 to 40 years of age Once the deterioration of the nervous system begins the condition is irreversible and fatal Huntington’s Disease: A Late-Onset Lethal Disease © 2011 Pearson Education, Inc.

99. Multifactorial Disorders Many diseases, such as heart disease, diabetes, alcoholism, mental illnesses, and cancer have both genetic and environmental components Little is understood about the genetic contribution to most multifactorial diseases © 2011 Pearson Education, Inc.

100. Genetic Testing and Counseling Genetic counselors can provide information to prospective parents concerned about a family history for a specific disease © 2011 Pearson Education, Inc.

101. Counseling Based on Mendelian Genetics and Probability Rules Using family histories, genetic counselors help couples determine the odds that their children will have genetic disorders Probabilities are predicted on the most accurate information at the time; predicted probabilities may change as new information is available © 2011 Pearson Education, Inc.

102. Tests for Identifying Carriers For a growing number of diseases, tests are available that identify carriers and help define the odds more accurately © 2011 Pearson Education, Inc.

103. Figure 14.18

104. Fetal Testing In amniocentesis, the liquid that bathes the fetus is removed and tested In chorionic villus sampling (CVS), a sample of the placenta is removed and tested Other techniques, such as ultrasound and fetoscopy, allow fetal health to be assessed visually in utero © 2011 Pearson Education, Inc. Video: Ultrasound of Human Fetus I

105. Figure 14.19 (a) Amniocentesis (b) Chorionic villus sampling (CVS) Ultrasound monitor Amniotic fluid withdrawn Fetus Placenta UterusCervix Centrifugation Fluid Fetal cells Several hours Several weeks Biochemical and genetic tests Karyotyping Ultrasound monitor Fetus Placenta Chorionic villi Uterus Cervix Suction tube inserted through cervix Several hours Fetal cells Several hours 11223

106. Newborn Screening Some genetic disorders can be detected at birth by simple tests that are now routinely performed in most hospitals in the United States © 2011 Pearson Education, Inc.

107. Figure 14.UN06