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CHAPTER 11 MENDELIAN PATTERNS OF INHERITANCE Chapter Outline 11.1 Gregor Mendel 1. Mendel was an __________________ monk. 2. Mendel formulated two fundamental laws of heredity in the early __________________. 3. He had previously studied science and __________________ at the University of Vienna. 4. At time of his research, he was a __________________ science teacher at a local technical high school. 5. Prior to Mendel’s work, investigators had been trying to support a “__________________” concept of __________________. A. Blending Concept of Inheritance 1. This theory stated that offspring would have traits __________________ between those of the parents. 2. Red and white flowers produce __________________ flowers; any return to red or white offspring was considered instability in the __________________ material. 3. Charles Darwin wanted to develop a theory of __________________ based on hereditary principles; __________________ theory was of _____________ help. a. A blending theory did not account for variation (differences) and could not explain species diversity. b. The particulate theory of __________________ proposed by Mendel can account for presence of __________________ among members of a population __________________ after __________________. c. Mendel’s work was unrecognized until __________________; Darwin was never able to use it to __________________ his theory of __________________. B. Mendel’s Experimental Procedure 1. Because Mendel had a __________________ background, he used a __________________ basis for his breeding __________________. 2. Mendel prepared his experiments __________________ and conducted preliminary studies. a. He chose the __________________, Pisum sativum, because peas were easy to culti__________________ vate, had a __________________ generation time, and could be __________________ -pollinated by hand. b. From many __________________, Mendel chose __________________ true-breeding varieties for his __________________. c. __________________ varieties had all offspring __________________ the parents and __________________ each other. d. Mendel studied __________________ traits (e.g., seed __________________ and __________________, flower __________________, etc.). 3. Mendel traced __________________ of individual traits and kept careful records of __________________. 4. 5. He used his understanding of mathematical principles of __________________ to interpret results. He arrived at a particulate theory of __________________ because it is based on the existence of minute particles—now called __________________. 11.2 Mendel’s Laws: Law of Segregation 1. Mendel confirmed that his __________________ plants always had __________________ offspring, i.e., were __________________, before crossing two __________________ strains that differed in only one trait—this is called a __________________ cross. 2. A monohybrid cross is between __________________ parent organisms true-breeding for __________________ distinct forms of __________________ trait. 3. Mendel tracked each trait through __________________ generations. a. __________________ is the parental generation in a breeding experiment. 58 b. __________________ is the first-generation offspring in a breeding experiment. c. __________________ is the second-generation offspring in a breeding experiment. 4. He performed reciprocal crosses, i.e. pollen of __________________ plant to stigma of __________________ plant and vice versa. 5. His results were __________________ to those predicted by a blending theory of __________________. 6. He found that the F1 plants resembled only __________________ of the parents. 7. Characteristics of other parent __________________ in about __________________ of F 2 plants; __________________ of offspring resembled the F 1 plants. 8. Mendel saw that these __________________ results were possible if: a. F1 hybrids contained __________________ factors for each trait, one being __________________ and the other __________________; b. factors __________________ when gametes were formed; a gamete carried __________________ copy of each factor; c. and random __________________ of all possible gametes occurred upon __________________. 9. Results of his experiments led Mendel to develop his first law of inheritance—the __________________: a. Each organism contains __________________ factors for each trait. b. Factors __________________ in the formation of gametes. c. Each __________________ contains __________________ factor for each trait. d. Fertilization gives each __________________ individual __________________ factors for each trait. A. As Viewed by Modern Genetics 1. Each trait in a pea plant is controlled by __________________ alleles, alternate forms of a gene that occur at the __________________ gene locus on __________________ chromosomes. 2. A __________________ allele masks or __________________ expression of a __________________ allele; it is represented by an __________________ letter. 3. A __________________ allele is an allele that exerts its effect only in the __________________ state; its expression is __________________ by a dominant allele; it is represented by a __________________ letter. 4. The __________________ is the specific __________________ of alleles on __________________ chromosomes. 5. The process of __________________ explains Mendel’s law of __________________. 6. In Mendel’s cross, the parents were true-breeding; each parent had __________________ identical alleles for a trait–they were __________________, indicating they possess __________________ identical alleles for a trait. 7. __________________ __________________ genotypes possess __________________ dominant alleles for a trait. 8. __________________ __________________ genotypes possess two __________________ alleles for a trait. 9. After cross-pollination, all individuals of the F1 generation had __________________ of each type of __________________. 10. __________________ genotypes possess __________________ of each allele for a particular trait. 11. The allele not expressed in a __________________ is a recessive allele. B. Genotype Versus Phenotype 1. Two organisms with different allele combinations can have the same outward appearance (e.g., __________________ and __________________ pea plants are both __________________; therefore, it is necessary to distinguish between alleles present and the __________________ of the organism). 2. __________________ refers to the alleles an individual receives at fertilization (dominant, recessive). 3. __________________ refers to the physical __________________ of the individual (tall, short, etc.). C. One-trait Genetics Problems 1. First determine which characteristic is __________________; then code the alleles involved. 2. Determine the __________________ and gametes for both parents; an individual has two alleles for each __________________; each gamete has only one allele for each trait. 3. Each gamete is __________________; each has a 50% chance of __________________ either allele. 59 D. Laws of Probability 1. __________________ is the likely outcome a given event will occur from __________________ chance. a. For example, with every coin flip there is a __________________ chance of heads and __________________ chance of tails. b. Chance of inheriting one of either two alleles from a parent is also __________________ 2. The multiplicative law of probability __________________ that the chance of two or more __________________ events occurring together is the product of the probability of the events occurring separately. a. The chance of inheriting a specific allele from one parent and a specific allele from another is ½ x ½ or __________________ b. Possible combinations for the alleles __________________ of heterozygous parents are the following: EE = ½ x ½ = _____, eE = ½ x ½ = _____,Ee = ½ x ½ = ¼, ee = ½ x ½ = _____ 3. The additive law of probability __________________ the probability of an event that occurs in __________________ or more independent ways; it is the __________________ of individual probabilities of each way an __________________ can occur; in the above example where __________________ earlobes are __________________ (EE, Ee, and eE), the chance for unattached earlobes is 1/4 + 1/4 + 1/4 = 3/4. E. The Punnett Square 1. The __________________ square was introduced by R. C. Punnett (early 1900s) and provides a simple method to __________________ the probable results of a genetic cross. 2. In a Punnett square, all possible __________________ of sperm alleles are lined up vertically and all possible egg alleles are lined up horizontally; every possible combination is __________________ in squares. 3. The larger the sample size __________________, the more likely the outcome will reflect __________________ ratios; a large number of offspring must be counted to observe the __________________ results; only in that way can all possible genetic types of sperm __________________ all possible types of eggs. 4. Specific crosses in __________________ cannot be done in order to count many offspring; therefore in humans, the __________________ ratio is used to estimate the probability of any child having a __________________ characteristic. 5. Punnett square uses laws of __________________; it does not dictate what the next child will __________________. 6. “Chance has no __________________”: if two heterozygous parents have a first child with attached earlobes (likely in 1/4th of children), a second child born still has __________________ chance of having attached earlobes. F. One-Trait Testcross 1. To confirm that the F1 was __________________, Mendel crossed his F1 plants with __________________ __________________ plants. 2. Results indicated the __________________ factor was present in the F1 plants; they were thus __________________. 3. A monohybrid __________________ is used between an individual with dominant phenotype and an individual with a recessive phenotype to see if the individual with dominant phenotype is __________________ or __________________. Mendel’s Law of Independent Assortment 1. This two-trait (__________________) cross is between two parent organisms that are true-breeding for different forms of __________________ traits; it produces offspring heterozygous for both traits. 2. Mendel observed that the F1 individuals were __________________ in both traits. 3.. He further noted __________________ phenotypes among F2 offspring; he deduced second law of heredity. 4. Mendel’s law of __________________ assortment states that members of __________________ pair of factors assort __________________ of members of another pair, and that all __________________ of factors occur in gametes. 60 A. Two-trait Genetics Problems 1. Laws of probability indicate a __________________ phenotypic ratio of F2 offspring resulting in the following: a. 9/16 of the offspring are __________________ for both traits; b. 3/16 of the offspring are __________________ for one trait and recessive for the other trait; c. 3/16 of the offspring are __________________ and recessive opposite of the previous proportions; and d. 1/16 of the offspring are __________________ for both traits. 2. The Punnett Square for two-trait crosses a. A larger __________________ square is used to calculate probable results of this cross. b. A phenotypic ratio of __________________ is expected when heterozygotes for two traits are crossed and simple __________________ is present for both genes. c. __________________ __________________ during __________________ explains these results. B. Two-Trait Testcross 1. A two-trait __________________ tests if individuals showing two dominant characteristics are __________________ for both or for one trait only, or heterozygous for both. 2. If an organism heterozygous for two traits is crossed with another recessive for both traits, the expected phenotypic ratio is __________________ 3. In __________________ genetics problems, the individual has four alleles, two for each __________________. 11.3 Human Genetic Disorders A. Patterns of Inheritance 1. Genetic disorders are medical conditions caused by __________________ inherited from parents. 2. An __________________ is any chromosome other than a sex (__________________) chromosome. 3. In a __________________ chart, males are designated by squares, __________________ by circles; shaded circles and squares are __________________ individuals; line __________________ square and circle represents a union; __________________ line leads to offspring. 4. A __________________ is a heterozygous individual with __________________ apparent abnormality but able to pass on an allele for a recessively-inherited genetic disorder. 5. Autosomal dominant and autosomal recessive alleles have __________________ patterns of inheritance. a. Characteristics of autosomal dominant disorders 1) __________________ children usually have an affected parent. 2) __________________ are affected.: two affected parents can produce unaffected child; two unaffected parents will not have __________________ children. b. Characteristics of autosomal recessive disorders 1) Most affected children have __________________ parents since heterozygotes have a __________________ phenotype. 2) Two affected parents always produce an __________________ child. 3) Close __________________ reproduce together are more likely to have __________________ children. B. Autosomal Recessive Disorders 1. Tay-Sachs Disease a. Usually occurs among __________________ people in the U.S. of central and eastern __________________ descent. b. Symptoms are not __________________ apparent; infant’s development begins to slow between four to eight __________________, neurological and psychomotor __________________ become apparent, child gradually becomes __________________ and helpless, develops __________________, eventually becomes paralyzed and __________________ by age of three or four. c. This results from lack of __________________ hexosaminidase A (Hex A) and the subsequent storage of its substrate, glycosphingolipid, in __________________. d. Primary sites of storage are cells of the __________________; accounts for progressive __________________. e. There is __________________ treatment or cure. 61 f. Prenatal diagnosis is __________________ by amniocentesis or chorionic villi sampling. g. The gene is located on chromosome __________________ 2. Cystic Fibrosis a. This is the most common __________________ genetic disease in Caucasians in the U.S. b. About 1 in 20 Caucasians is a __________________, and about 1 in 3,000 newborns has this disorder. c. An __________________ production of a viscous form of __________________ in the __________________ and pancreatic ducts is seen. 1) The resultant __________________ 2) Digestive enzymes must be __________________ with food to supplant the pancreatic __________________. d. New __________________ have raised the average life expectancy to up to __________________ years. e. Chloride ions (Cl–) fail to pass __________________ membrane proteins. f. Since water normally follows Cl–, lack of __________________ in the lungs causes thick __________________. g. The cause is a gene on chromosome __________________; __________________ to insert the gene into nasal epithelium has had __________________ success. h. __________________ testing for adult carriers and fetuses is possible. 3. Phenylketonuria (PKU) a. PKU occurs once in every __________________ births; it is the most common __________________ disease of the __________________ system. b. It is caused by a lack of an __________________ needed to metabolize amino acid phenylalanine; this results in __________________ of the amino acid in nerve cells of the __________________ and impairs nervous system development. c. PKU is caused by a gene on chromosome __________________ d. __________________ are routinely tested in the hospital for high levels of phenylalanine in the __________________. e. If an infant has PKU, the child is placed on a diet __________________ in phenylalanine until the brain is fully developed, near age __________________. 4. Sickle-Cell Disease a. This __________________ is the most common inherited disorder in blacks, affecting about 1 in 500 African Americans. b. The gene is on chromosome __________________. c. In affected individuals, the __________________ are shaped like sickles—an abnormal hemoglobin molecule, Hbs, causes the __________________. 1) Normal hemoglobin, HbA, differs from Hbs by __________________ amino acid in the protein globin. d. The disease is an example of pleiotropy, describing a gene that affects more than one __________________ of an individual. e. Sickling of the __________________ occurs when the oxygen content of the person’s blood is __________________, thereby slowing down blood flow and __________________ small vessels. f. Signs and symptoms include __________________, weakness, fever, pain, rheumatism, __________________ resistance to disease, kidney and heart failure. g. Treatment includes __________________ management, blood __________________, and bone marrow __________________. h. The disease can be diagnosed __________________. i. Individuals with the sickle cell trait (__________________), who normally do not have any sickle-shaped cells unless they experience __________________ or mild oxygen deprivation, are resistant to the disease __________________. C. Autosomal Dominant Disorders 1. Neurofibromatosis a. This is an __________________ dominant disorder that affects one in 3,500 newborns and is distributed __________________ around the world. 62 b. Affected individuals have __________________ skin spots at birth, which develop into __________________ tumors. c. Neurofibromas are __________________ under the skin comprised of fibrous coverings of nerves. d. In most cases, symptoms are mild and patients live a __________________ life; sometimes symptoms are __________________: 1) __________________ deformities, including a large head; 2) eye and ear __________________ that can lead to blindness and hearing loss; and 3) learning __________________ and hyperactivity. 4) Such __________________ is called variable expressivity. e. The gene that codes for neurofibromatosis was discovered in __________________ to be on chromosome 17. 1) The gene controls production of neurofibromin __________________ that normally blocks growth signals for __________________ 2) Many types of __________________ result in this effect. 3) Some mutations are caused by a __________________ that moves from another location in the __________________. 2. Huntington Disease a. This leads to progressive __________________ of brain cells, which in turn causes severe muscle __________________, personality __________________, and death in __________________ years after onset. b. Most appear __________________ until they are of __________________ and already have had __________________ who might __________________ the gene; occasionally, first signs of the disease are seen in __________________ or even younger. c. The gene for Huntington disease is located on chromosome __________________ d. This gene contains many repeats of a base __________________ that codes for glutamine in the huntingtin __________________; normal persons have 10–15 glutamines; affected persons have 36 or more. e. A huntingtin protein with over 36 glutamines __________________ shape and forms large clumps inside __________________; it also attracts other proteins to __________________ with it. 3. Achondroplasia a. This disease is a common form of __________________, associated with a defect in the growth of long bones. b. Affected individuals have __________________ arms and legs, a sway __________________, and a normal torso and __________________. c. About 1 in 25,000 people have the __________________. d. Individuals with the disease are __________________ (Aa); the homozygous recessive (aa) condition yields __________________ -length limbs, while the homozygous __________________ (AA) condition is __________________. 11.4 Beyond Mendelian Genetics A. Incomplete Dominance 1. Incomplete dominance: offspring show traits __________________ between two parental phenotypes. a. __________________ red and white-flowered four-o’clocks produce pink-flowered offspring. b. __________________ __________________ has a biochemical basis; the level of gene-directed protein production may be between that of the __________________ homozygotes. c. One allele of a __________________ pair only partially dominates expression of its partner. d. This does not support a __________________ theory; parental phenotypes reappear in F2 generation. B. Human Examples of Incomplete Dominance 1. Curly versus Straight Hair a. A curly-haired Caucasian and a straight-haired Caucasian will have __________________ -haired offspring. b. Two wavy-haired parents will produce a 1:2:1 ratio of curly-wavy-straight hair children. 2. Sickle-cell disease, Tay Sachs disease, and cystic fibrosis are considered examples of 63 __________________ C. Multiple Allelic Traits 1. This occurs when a gene has many allelic forms or __________________ expressions. 2. __________________ Blood Types a. The ABO system of human blood types is a __________________ allele system. b. Two __________________ alleles (IA and IB) code for presence of A and B glycoproteins on __________________. c. This also includes a __________________ allele (iO) coding for no A or B glycoproteins on red blood cells. d. As a result, there are __________________ possible phenotypes (blood types): A, B, AB, and O e. This is a case of __________________, where both alleles are fully expressed. 3. The Rh factor is inherited independently from the ABO system; the Rh+ __________________ is __________________. D. Polygenic Inheritance 1. Polygenic inheritance occurs when __________________ trait is governed by __________________ or more sets of alleles. 2. __________________ alleles have a quantitative effect on the phenotype: each adds to the __________________. 3. The more genes involved, the more __________________ is the variation in phenotypes, resulting in a __________________. 4. Crosses of white and dark-red wheat seeds produce seeds with __________________ degrees of __________________ colors due to genes at three separate loci. 5. Human Examples of Polygenic Inheritance a. A hybrid cross for __________________ color provides a range of intermediates. b. Parents with intermediate skin color can produce children with the full range of __________________ c. __________________, where one gene __________________ with the expression of others, is an example of epistasis. E. Polygenic Disorders 1. This includes __________________, clubfoot, congenital dislocations of the hip, __________________, __________________, schizophrenia, allergies and __________________. 2. Behavioral traits including __________________, phobias, alcoholism, and homosexuality may be __________________ with particular genes but are not likely completely __________________. 3. Environment and the Phenotype a. In water buttercups, the aquatic environment dramatically __________________ the structure of the plant. b. __________________ triggers a primrose to develop white flowers when grown above 32 oC and red flowers when grown at 24oC. c. The coats of Siamese cats and Himalayan rabbits have __________________ tipped ears, nose, paws, etc. due to the __________________ encoded by an allele which is only active at the __________________ at low temperatures. F. Environment and the Phenotype 1. Both genotype and the environment affect the __________________. 2. Water and temperature can have profound __________________ on the phenotype. a. A flower might be one color at one __________________ and another color at another temperature. b. The coat color of certain animals can change with __________________. 11:B Chromosomal Inheritance 1. 2. _______________ are located on chromosomes; this is called the chromosome theory of inheritance. Chromosomes can be categorized as two types: a. _______________ are non-sex chromosomes that are the same number and kind between sexes. b. _______________ determine if the individual is male or female. 64 3. 4. Sex chromosomes in the human female are _______; those of the male are ________. Males produce ____-containing and _______-containing gametes; therefore males determine the _____________of offspring. 5. Besides genes that determine sex, sex chromosomes carry many _______________ for traits unrelated to _______________. 6. An _______________ is any gene located on X chromosome; used to describe genes on X chromosome that are missing on the _________chromosome. A. X-Linked Alleles 1. Work with fruit flies (Drosophila) by Thomas Hunt Morgan (early 1900s) confirmed genes were on _______________. a. Fruit flies are easily and inexpensively raised in common _______________ glassware. b. Females only mate _______________ and lay hundreds of _______________. c. The fruit fly generation time is _______________, allowing rapid experiments. 2. Fruit flies have an_______________ sex chromosome system similar to the human system; experiments can be correlated to the _______________ situation. a. Newly discovered mutant male fruit flies had _______________ eyes. b. Cross of the hybrids from the white-eyed male crossed with a dominant red-eyed female yielded the expected _______________ red-to-white ratio; however, all of the white-eyed flies were _______________. c. An allele for eye color on the X but not on the Y _______________ supports the results of this cross. d. Behavior of this allele corresponds to the behavior of the chromosome; this confirmed the _____________________________________________. 3. X-Linked Problems a. X-linked alleles are designated as superscripts to the ___________chromosome. b. Heterozygous females are _______________; they do not show the trait but can transmit it. c. Males are never carriers but express the one allele on the ____________chromosome; the allele could be dominant or recessive. d. One form of color-blindness is X-linked _______________. B. Human X-Linked Disorders 1. More _______________ have X-linked traits because recessive alleles on the X chromosome in males are _______________ in males. 2. Color Blindness a. Color blindness can be an _______________ disorder involving mutations of genes coding for green or red sensitive cone cells, resulting in the inability to perceive green or red, respectively; the pigment for blue-sensitive protein is _______________. b. About 8% of Caucasian men have red-green _______________. 3. Muscular Dystrophy a. Duchenne muscular dystrophy is the most common form and is characterized by wasting away of _______________, eventually leading to death; it affects one out of every 3,600 _______________ births. b. This X-linked recessive disease involves a _______________ gene that fails to produce the _______________ dystrophin. c. Signs and symptoms (e.g., waddling gait, toe walking, frequent _______________, difficulty in _______________) soon appear. d. Muscles weaken until the individual is confined to a wheelchair; death usually occurs by age _______________. e. Affected males are _______________ fathers; the gene passes from carrier mother to _______________ daughter. f. Lack of dystrophin protein causes calcium ions to leak into _______________ cells; this promotes action of an _______________ that dissolves muscle fibers. g. As the body attempts to _______________ tissue, fibrous tissue forms and cuts off blood supply to the affected _______________. h. A test now detects carriers of Duchenne muscular dystrophy; _______________ are being attempted. 3. Hemophilia 65 a. 4. About one in 10,000 males is a _______________ with impaired ability of blood to _______________. b. The two common types: Hemophilia A, due to the _______________ of clotting factor IX; Hemophilia B, due to the absence of clotting factor VIII. c. Hemophiliacs bleed _______________ after an injury and also suffer internal bleeding around _______________. d. Hemorrhages stop with _______________ of blood (or plasma) or concentrates of clotting protein. e. Factor VIII is now available as a _______________ -engineered product. f. Of Queen Victoria’s 26 offspring, _______________ grandsons had hemophilia and four granddaughters were _______________. Fragile X Syndrome (See Health and Focus box) a. In this case, the X chromosome is nearly _______________; most often found in males. b. This affects one in 1,500 _______________ and one in 2,500 females. c. As children, they are often _______________ or autistic with delayed or repetitive speech. d. As adults, males usually have _______________ testes, unusually protruding _______________, and other symptoms. e. About one-fifth of males with _______________ X do not show symptoms. f. Fragile X passes from a symptomless female carrier to grandson. g. It has been traced to excessive repeats of base triplet _______________ (cytosine-guanineguanine); up to 230 copies compared to normal 6–to–50 copies. 66