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Lab Exercise 15 Human Genetics Introduction Contents Activity 15.1 Activity 15.2 Activity 15.3 Objectives Introduction Human Karyotype Some Human Traits Pedigree Analysis Resutls Section Objectives - Become familiar with the human karyotype. - Be able to recognize abnormal karyotypes. - Be able to diagram a pedigree for a specific trait. - Be able to interpret a pedigree for a specific trait. 1 1 2 2 4 5 While Mendelian genetic principles apply to humans just as they apply to all other organisms, as a society we constrain ourselves from conducting breeding experiments on human subjects in an effort to gather information on the nature of inherited traits. Consequently we rely on other sources of information to obtain this knowledge. One source of information comes from study of the human karyotype, the number and appearance of our chromosomes. Another source of information is from the study and interpretation of pedigrees. The number and appearance of the chromosomes as they enter metaphase is called an organism’s karyotype. Irregularities seen in an individual’s karyotype usually lead to abnormalities which in most cases are quite detrimental to the individual. The first exercise in the lab has you examine the human karyotype and then look at some of the abnormalities which may occur. When using pedigree analysis to study the nature of inheritance of particular traits, families are investigated to determine which individuals within the family possess the trait in question. Then using deductive reasoning, the nature of the trait’s inheritance in inferred. The second exercise in this lab asks you to determine your phenotype for some inherited traits. The third exercise involves the construction and interpretation of pedigrees. Ramp. Copyright © 2012 by F.one Design. All rights reserved. 15 1 Activity 15.1 Human Karyotype Activity 15.2 Pedigree Analysis An individual’s karyotype is the appearance and number of the chromosomes in their cells. The normal human karyotype consists of 22 pairs of chromosomes of various sizes plus a pair of sex chromosomes for a total of 46 chromosomes. Examine the normal chromosomes of a normal human karyotype in the Human Genetics simulation on the BiologyOne DVD. Then examine and read about some of the abnormal karyotypes that occur. These abnormalities are the result of chromosomes failing to separate properly during meiosis, events that are referred to as nondisjunctions. Since it is neither practical nor morally acceptable to breed humans in an effort to determine the nature of genetic inheritance of specific traits, scientists rely on another method to infer modes of inheritance. This is the study of family trees or pedigrees. By analyzing the pedigree, one may be able to deduce how a gene for a specific trait is inherited. Examine the chromosomes displayed in the Results Section. These are how they would appear through the microscope when stained. Try cutting these out and arranging these to show the individual’s karyotype. Use the chromosome size, location of the centromere and banding patterns to pair chromosomes. Does this individual have a normal karyotype? What is their sex? You can also try constructing a karyotype using the illustration of the chromosomes in the Results Section (this will probably be easier than pairing with the images of the actual chromosomes). What is this individual’s sex? Is their kryotype normal? In a pedigree analysis, individuals are represented by symbols. Open shapes usually represent individuals who do not express the trait while filled shapes represent individuals who express the trait being investigated. If heterozygous individuals can be determined they are usually represented by partially filled shapes. Unions and the offspring from unions are represented in the pedigree by connecting lines as indicated in below. Study the examples of a pedigrees shown in the Results Section and then answer the questions concerning the other pedigrees. Use the information in the Results Section to construct a pedigree. If you were able to collect information from your family for some of the genetic traits listed in section 15.2, select one of those traits and construct the pedigree for your family for that trait. Symbols used in Pedigree Charts male without trait female with trait male carrier individual of unknown sex male with trait identical twins male/femlae union female without trait siblings female carrier Ramp. Copyright © 2012 by F.one Design. All rights reserved. fraternal twins 15 2 Activity 15.3 Some Human Traits Through pedigree analysis, a number of human characteristics have been determined to be controlled by a single gene and are easily demonstrated to follow Mendelian laws of inheritance and the Hardy-Weinberg predictions. Several of these traits will be explored in this exercise. Use the following descriptions of traits to determine your phenotype and possible genotype(s). Record your observations in the Report Section. If you are able, also determine the phenotypes of your relatives. Your instructor may also collect data from the class to determine the population frequencies for these traits. Hitch-hiker’s Thumb. If you can bend the tip of your thumb backwards so that the last joint is nearly a right angle to the rest of your thumb, you have what is called a hitchhiker’s thumb. Hitch-hiker’s thumb is recessive (h) to a non-hitch-hiker’s thumb (H). Dimples. One or more facial dimples (D) is dominant over no dimples (d). Tongue Rolling. The ability to roll one’s tongue lengthwise is a genetic inherited trait. The ability to roll your tongue (R) is dominant to the inability to roll your tongue (r). Freckles. Freckles (F) are dominant over no freckles (f). Widow’s Peak. If your hairline forms a point in the middle of your forehead you have what is called a widow’s peak. The allele for a widow’s peak (P) is dominant to no widow’s peak. Interlace Fingers. Clasp your hands together and look at the position of your thumbs. If your left thumb is over the right thumb, you have the dominant phenotype (II or Ii). If your right thumb is over your left thumb you have the recessive phenotype (ii). Red-green Color Blindness. This is a sex-linked, recessive trait. Since females have two copies of the X chromosome, normal color vision females can be either CC or Cc while color blind females will be cc. Normal males will have the genotype CY and color blind males will be cY. At the end of the Human Genetics simulation on the BiologyOne CD is a color dot pattern you can use to test your color vision but use the results of this test with caution since computer color displays are somewhat variable. Bent Phalanges. If you hold your hands with your palms toward you and the last joints of your little fingers flare away from each other, you have the trait known as bent phalanges. Bent phalanges (B) is dominant over straight phalanges (b). Earlobes. If your earlobes hang below the point where your ear attaches to your head, you have free earlobes. If they do not hang down, you have attached earlobes. Free earlobes (E) are dominant to attached earlobes (e). Long Palmar Muscle. When you clench both fists, palms up, and slowly rotate your hand, do you see two or three tendons in your wrist. If you only see two tendons in both wrists you do not have long palmar muscles and your genotype is pp. If both wrists have three tendons, you are probably homozygous for this trait (genotype PP). If only one wrist has three tendons, you are probably heterozygous (Pp). Ramp. Copyright © 2012 by F.one Design. All rights reserved. 15 3 Illustration of Some Human Traits attached earlobe free earlobe straight hairline bent phalanges straight phalanges Ramp. Copyright © 2012 by F.one Design. All rights reserved. widow’s peak 15 4 Lab Exercise 15 Name _______________________ Results Section Activity 15.1 Human Karyotype Cut out the photograph of chromosomes on the next page and arrange them in pairs in the spaces below. Chromosome pairs are numbered from largest chromosomes to smallest with the sex chromosomes shown last. ________ 1 ________ 2 ________ 3 ________ 4 ________ 5 ________ 6 ________ 7 ________ 8 ________ 9 ________ 10 ________ 11 ________ 12 ________ 13 ________ 14 ________ 15 ________ 16 ________ 17 ________ 18 ________ 19 ________ 20 ________ 21 ________ 22 ________ sex Ramp. Copyright © 2012 by F.one Design. All rights reserved. 15 5 Chromosomes Ramp. Copyright © 2012 by F.one Design. All rights reserved. 15 6 Cut out the illustration of chromosomes on the next page and arrange them in pairs in the spaces below. Chromosome pairs are numbered from largest chromosomes to smallest with the sex chromosomes shown last. ________ 1 ________ 2 ________ 3 ________ 4 ________ 5 ________ 6 ________ 7 ________ 8 ________ 9 ________ 10 ________ 11 ________ 12 ________ 13 ________ 14 ________ 15 ________ 16 ________ 17 ________ 18 ________ 19 ________ 20 ________ 21 ________ 22 ________ sex Ramp. Copyright © 2012 by F.one Design. All rights reserved. 15 7 Chromosomes Ramp. Copyright © 2012 by F.one Design. All rights reserved. 15 8 Activity 15.2 Pedigree Analysis Example of pedigree analysis: The following pedigree is for myopia (nearsightedness). What is the nature of its inheritance? 1 5 2 6 7 8 3 4 9 10 11 12 13 14 Analysis: 1. The trait appear to be equally expressed in males and female so it is likely not sex linked. 2. The trait occurs in individual #1 but in none of his children and the trait does not occur in parents 3 and 4 but does occur in their children. Conclusion: the allele for this trait is probably recessive. Test of conclusion: If the allele for myopia is recessive, individauls 1, 11, and 13 must be homozygous for this trait. Others may be heterozygous or homozygous non-myoptic. Each child from parents 1 and 2 would be heterozygous, inheriting the myoptic allele from their father. For individual 11 to inherit the trait from parents 3 and 4, both parents must be heterozygous. They would then be expected to have 1 out of 4 children with the trait (lucky here). Each normal child would have a 2/3 chance of being heterozygous. Diagram a Pedigree In the below space, diagram a family pedigree in which a couple has 5 children, 3 boys and 2 girls. One of the girls and a boy are fraternal twins. The mother’s phenotype displays the trait in question. Two of the boys (not the twin) and the twin girl display this phenotype as well. One of the boys, not the twin, marries a woman who does not express this phenotype. They have two girls, neither of which has this phenotype. Ramp. Copyright © 2012 by F.one Design. All rights reserved. 15 9 Interpreting a Pedigree The trait denoted in the following pedigree is known to be recessive. Answer the below questions. 1 3 9 5 4 10 2 6 7 11 1. What is the possible genotype of individual #1? For individual #4? 2. Do you think this is trait is sex-linked? Ramp. Copyright © 2012 by F.one Design. All rights reserved. 15 10 9 If you collected family data for the human traits - construct a pedigree of your family below Ramp. Copyright © 2012 by F.one Design. All rights reserved. 15 11 Activity 15.3 Some Human Traits Your phenotype Father's phenotype & genotype Mother's phenotype & genotype & genotype Tongue Rolling Freckles Widow's Peak Bent Phalanges Earlobes Long Palmar Muscle Hitch-hiker's Thumb Dimples Interlace Fingers Red-gree Color Blindness Ramp. Copyright © 2012 by F.one Design. All rights reserved. 15 12 Sibling phenotypes % of class & genotypes with trait