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1 Name________________________________________________Score_________ Section_______________________________________________Date____________ EXERCISE NO. 6 HUMAN GENETICS OBJECTIVES The students should be able to 1. determine the pattern of inheritance of some human traits and abnormalities; 2. arrange chromosomes in correct order to make a karyotype; 3. analyze this karyotype of human chromosomes to identify genetic disorders. MATERIALS Family Pedigree Photographs of C-metaphase human chromosomes spreads (to be given by instructor) Filter paper cut into 1 x ½ inch squares 0.5% aqueous PTC solution PROCEDURE A. Family Pedigree 1. Submit your family pedigree on a given trait. The pedigree should include your parents and siblings. 2. With two other family pedigrees of classmates working on the same trait as yours, copy on your lab manual all three pedigree. B. Karyotype Analysis Using a given photograph of human chromosomes, construct a karyotype by cutting out the chromosomes and arranging them in as nearly matching pairs based on length, centromeres and satellites (if present) C. Some Inherited Human Characteristics a. Attached Ear Lobes. In most people, the ear lobes hang free, but when a person is homozygous for a certain recessive gene (e), the ear lobes are attached directly onto the side of the head so there is no lobe hanging free. By means of a mirror or with the help of your classmates, determine your phenotype for this characteristic Record results in Table 10-1. b. Widows Peak. In some people, the hair line drops downward and forms a distinct point in the center of the forehead. This is known as the widow’s peak. It results from the action of a dominant gene (W). Determine your phenotype by examining your front hair line for a widow’s peak or for a continuous hair line. c. Tongue Rolling. A dominant gene ( R ) gives some people the ability to roll the tongue into a distinct U-shape when the tongue is extended from the mouth. Other, who do not possess this gene can do no more than produce a slight downward curve of the tongue when it is extended from the mouth. 2 d. Bent Little Finger. A dominant gene (B) causes the last joint of the little finger to bend inward toward the fourth finger. Lay both hands flat on the table, relax the muscle and note whether you have a bent or straight little finger. e. Hitchhiker’s thumb. This characteristic can be determined by bending the outermost joint of the thumb back as far as possible. Some persons can bend it back until there is almost (but not quite) a 45o angle between the two joints. Evidence indicates that this trait is due to a recessive gene. Are both thumbs consistent? f. Mid-digital hair. Some people have hair on the second middle joint of the fingers while others do not. The complete absence of hair from all fingers is due to a recessive gene (m) and its presence due to a dominant gene (M). This hair may be very fine and you should use a hand lens and look very carefully on all fingers before deciding on your phenotype. g. Interlocking Fingers. When fingers are interlocked, some people will almost invariably place the left thumb on top of the right and others will place the right over the left. Studies indicate that placing of the left over the right is due to a dominant gene (F), while the right thumb on top is due to a recessive gene (f). DATA COLLECTED 1. A. Family Pedigree (Symbolize the probable genotype of each individual in the three pedigrees.) STUDENT 1 STUDENT 2 STUDENT 3 3 B. Karyotype Analysis 4 C. Some Inherited Human Disorders Table 6-2 OCCURRENCE OF SOME INHERITED HUMAN CHARACTERISTICS _____________________________________________________________________ Trait Your Phenotype Your Genotype Number in Class _____________________________________________________________________ Attached Ear Lobes _____________ _______________ _____________ Free Ear Lobes _____________ Widow’s Peak _____________ _______________ _______________ _____________ No Widow’s Peak _____________ _______________ Tongue-roller _____________ _______________ _____________ Non-tongue roller _____________ _______________ Bent Little Finger _____________ _______________ _____________ Straight Little Finger _____________ _______________ Hitchhiker’s Thumb _____________ _______________ _____________ No Hitchhiker’s Thumb____________ _______________ W/ mid-digital hair _______________ ____________ _____________ No mid-digital hair _____________ Left thumb on top _____________ _______________ _______________ _____________ Right thumb on top _____________ _______________ _____________________________________________________________________ 5 QUESTIONS 2. Based on the family pedigrees, what is the mode of inheritance possible for the trait? 3. From the data collected in Part 6-C, determine if dominance plays a role in the frequency of appearance of any phenotype. Explain your answer. 4. From the karyotype in Part 6-B, determine if a specific aberration (if any) is involved. Give the genetic consequences of this anomaly. 5. Research about the following genetic disorders: Tay-Sach’s disease, Thallasemia and Edward’s Syndrome. Find the cause, type of mutation and characteristics. 6. Do your results show that the ability to taste PTC is an inherited trait? If yes, describe the mode of transmission of the trait.