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CHAPTER a v/ iJ ^ CHROMOSOMES, GENES AND INHERITANCE 34-1 Laboratory lnvestigation: Human Heredity 34-2 Ghromosomes and Genes 34-3 Sex-Linked Traits 34-4 Sample Sex-Linked and Blood Type Problems 34-5 Sex-Linked and Blood Type Problem Set Ch 34 Chromosomes, Genes and lnheritance 33 Page Page Page Page Page 34 38 41 49 50 Cfropter 34 Cfi.romosoffLes, $erces arcf Infteritance you try to do sometfi.ing 1egond afiat gou fiorte a{reo"dy mastered, you usi$ neoer Brod. 'Un{zss Ralph Waldo Emerson 34-1 Laboratory lnvestigation Human HereditY -YouObjectiu" will determine which traits you posses from a list of described traits. You will then be expected to determine which members of your family also possess these traits and wjll fill in pedigree diagrams for your family, for each trait. To determine whether you can taste PTC, perform the following taste test: a. Find the petri dish marked NoRMAL PAPER, WITHOUT PTC. I l your for about 8 paper tongue on strip Taste 1 piece of this by placing the seconds. This will allow you to compare the normal taste of clean paper to the taste of PTC. I I Throw the tasted papers in the garbage can when finished. t I Don't set them on the lab tables' t l b. Now taste a piece of PTC paper taken from the petri dish marked PTC PAPER. Taste it in the manner described above. lf you can taste this chemical, you will taste a considerably strong bitter taste. There will be no mistaking this taste. 1 lf your PTC paper does not taste much different to you than the normal paper WITHOUT PTC, then you are unable to taste it due to certain inherited 1 genes in you and your family. Discard all tasted paper. I l. Ch 34 Chromosmes, Genes and lnherhance 34 Most of the other traits are easy to determine by observation. You will need your lab partne/s help in two of the cases. ln a person with an 'unattached ear lobe" the lobe of the ear hangs free from the face. Examine the diagram carefully. t I Examine both of your ears to determine which you have. t I Attached ear lobe Unattached ear lobe Some people can roll their tongue as shown in the diagram. Some cannot. To test for this trait, you are not to use your fingers to help roll your tongue. Examine the drawing on this page and try this. t l Tongue roller This trait, as well as the others, are determined by certain dominant and recessive genes. Some individuals have a relatively straight thumb. Others have a thumb thal angles 45o angle at the joint. This is called a "hitch hikels thumb." Which do you have? Non hitch hiker's thumb I Hitch hike/s thumb lf you examine the hair of your partner, you will find that the hair forms a whorl at the crown. This whorl will either be clockwise or counter-clockwise. Which do you and your partner have? (See the diagram.) @ Counterclockwise hair whorl Ch 34 Chromosomes, Genes and lnherhance 35 $ Clockwise hair whorl Create a chart like the one below and fill in the information. The way to tell if a trait is dominant or recessive is to determine how many in your class have the trait. The trait that the majority of people have is usually the dominant trait. Number in your class with each THAIT trait Genotype ls the trait dominant or recessive? of trait fi PTCTASTER orTt tt NON-TASTER TONGUE ROLLER NON_ROil FR ATTACHED EAR LOBE UNATTACHED LOBE HII-CH HIKER'S THUMB NON.HITCH HIKER'S THUMB CLOCKWISE HAIRWHORL @UNTER.CLOCKWSE HAIR WHORL On the chalk board you will find a chart similar to the one above. After you have determined which traits you possess, place your results on the chalk board with a tally mark after the appropriate trait. I 1 Examine the chart on the chalk board when most of the class have entered their tally marks. t I 1. How can you determine, from your chart above, which traits are dominant and which are recessive? Fill in the third column in your chafi showing .dominance and recessiveness. I I ln the last column of the chart, the genotype is given to you for PTC tasters and nontasters. You fill in the genotypes for the remaining traits. Determine which letters to use according to the standard rules for assigning symbols. Make your letters clearly so it is obvious which letters are capitals and which are lower case letters. t 1 Ch 34 Ghromosomes, Genes and lnheritance 36 DETERMINING HOW SOME OF THESE TRAITS HAVE BEEN PASSED TO YOU FROM OTHER MEMBEHS OF YOUR FAMILY To be done at home. Pick any 3 of the 6 traits that you worked with in this lab and see if you can determine the genotypes and phenotypes of other members of your family. lf you cannot obtain information about your natural mother or father, your teacher can assign arbitrary phenotypes for parents so you can complete the assignment. You will need to determine which characteristics are present in some of your relatives ab shown on the chart. By deduction, you are to determine the probable genotype of as many relatives as possible. lf you would like to take home some PTC taster papers to check members of your family, arrange this with your teacher. I t When at home, check as many members of your family as you can, for your 3 chosen traits. Record what you are able to determine. I I For each trait, determine the following: 2. See if you can determine your genotype for each trait by examining natural parents and sisters and brothers or other relatives. Provide all available information on each relative and explain how you determined your genotype. lf you can't determine your genotype, explain why. 3. List the phenotype and genotype (where possible) of each parent, bother, sister or other natural relative available. I'\ i I 5 at '\. \ i r{i ,.t \ ; t Ch 34 Chromosomas, GenEs and lnheritance 37 34-2 Chromosomes and Genes 1. Where in the cell are chromosomes found? Where are the genes located? Objectlve You will be expected to know that genes are located on chromosomes. Be able to describe whai happens to the genes and chromosomes during sex cell formation (meiosis). Chromosomes As the 19th century was coming to a close, biologists had observed chromosomes appearing in the nucleus of cells as they began to divide. lt wasn't until 1902 that Walter Sutton, a graduate student at Columbia University, provided evidence that the genes were located on or in the chromosomes. He believed ihat the parallel behavior of the chromosomes and genes was not coincidental and hypothesized that the genes must be on the chromosomes. Chromosomes occur in pairs. This can be shown by a simple exercise. Photograph the chromosomes in the nucleus of a human cell. Print a large photo of the 46 chromosomes. Use a scissors to cut out each of the 46 chromosomes. Arrange similar chromosomes together and we find that each chromosome has what appears to be an identical twin. lt is the same length and shape. This is true for all but one pair, the sex chromosomes.' One member of this pair is shorter than the other. The four pairs of chromosomes at the left illustrate the ffi%@ffi$qt,ffi#$*ry* ## Pair. a tall plant can that For example, in pea plants you learned have one'gene for tailness and one for shortness. Sutton's hypothesiJ states that the tall gene (T) is located on one chromosome and the short gene (t) is on the other I € #l K e * ## \r tr I chromosome. Examine the drawing at tl're'right. t I These & two genes for height are called alleles. Allele-s are pairs of corrdrp.onOing genes fof.a tr:ait that are located at the game position on each member of a piir of chromosomq-s. T and.t are alleles for height in pea plants. Other allele 'cO-rnninations aie TT and tt. Geries for other traits are located above and below the T gene on each chromosomes. They are also paired alleles' 2. What is an allele? Ch 34 Chromoemes, Genes and lnheritance 3. Draw a pair of chromosomes and place the genes for brown and blue eyes on the chromosomes to show how alleles are positioned. Label the position of each gene with an arrow. 4. How many pairs of chromosomes are found in human cells? Are all pairs represented by two identically shaped chromosomes? Explain. Gene Location and Separation at Sex Gell Formation The genes for one trait are located on a pair of similar chromosomes. What happens to these genes when the cell divides to form sex cells? ln the last unit you learned that cells in the human testis divide by meiosis. The cell containing 46 chromosomes divides in two steps, creating sperm cells each with 23 chromosomes. To understand what happens to the genes during meiosis and sex cell formation we will examine the formation of sex cells in the pea plant anther. We will follow only one pair of chromosomes. The same thing happens to all other pairs. The cell diagrammed on the next page has chromosomes with genes T (tall) and t (short) on them for height. Study the changes that take place from step to step so you can answer the questions that follow. Photo ol human chromosomes Continued on the next page >>> Ch 34 Chromosomes, Genes and lnheritance 39 Meiosis in Pea '# 1ffi'#) # 4 *@* 'ff d' Sperm cells Notice that each step and change is represented with a numbered arrow. 5. ls the parent plant tall or short? Explain how you decided. 6. What changes took place 7. in step 1? ln step-2 lhe chromosome pairs line up on the spindle fibers as the cell starts to divide the first time. What changes lollowed in steps 3 and 4? B. The two new cells next divide again in step steps 5 and 6? Ch 34 Chromosom€s, Genes and lnheritance 40 6. What changes can be observed in L Of the four sperm cells formed, what fraction contain a gene for tallness and what fraction contain a gene for shortness? Cells in the ovule of the plant undergo the same process when egg cells are formed. 10. lf four egg cells are formed in the ovary that are identical to the sperm cells in genetic type, what genotypes and phenotypes gre possible for offspring in a cross between these two plants? Give the fractions predicted for each genotype and phenotype. 34-3 Sex Linked Traits Objectlve When you have completed this program, you should be able to describe how chromosomes determine your sex and how colorblindness, muscular dystrophy and hemophilia are passed from generation to generation. You will be expected to apply these principles in solving sex-linked genetic cross problems. Did you ever wonder why more men are colorblind than women? The reason is that these genetic traits are linked up with maleness. This program is designed to provide you with the understanding to be able to solve problems involving sex-linked traits. You will have opportunity to practice sample problems. Your understanding and ability to apply these principles will be evaluated with two sets of home assignment problems that follow. BEFORE GOING ON, PLACE YOUR PAPER OVER THE ANSWERS. 1. When a cell nucleus is photographed, the chromosomes look something like the drawing below. .- \ \,1 ir.S=*Yr{\} Jr*}L What are the individual units that are found on each chromosome that determine hereditary traits? 1. Genes Ch 34 Chromosomes, Genes and lnheritance 41 2. Human body cells contain how many chromosomes? Each egg or sperm cell contains how many chromosomes? 2. g. 46, 23 Each body cell contains 46 chromosomes or 23 pairs of chromosomes. lf the chromosomes from the photograph in 1 above were paired up they would look like the drawing below. II )(X x,t N' II [[ ffi 11[ hh xk ru tt IX XX \l\ \\ II ff rn ilil tl \\ Note that for each pair, the 2 chromosomes look alike except for one pair. ( The pair in the box.) One of the chromosomes of this pair is shorter and has a curled end. This pair of chromosomes is called the sex chromosomes. The long one is called the X chromosome and the short one is called the Y chromosome. Human cells have 22 pairs of body cell chromosomes and 1 pair of sex chromosomes, the X and Y chromosomes. Every female has 22 pairs of body chromosomes and 1 pair of sex chromosomes which are both X's. (XX) Body chromosomes and the sex chromosomes have thousands of genes on each chromosome. Every male has 22 pairs of body chromosomes and 1 pair of sex chromosomes, one an X and 1 a Y chromosome. On your own paper draw an X and a Y chromosome. I 4. lf a fertilized egg received 2 X's (XX) it would result in a (male or female). lf a fertilized egg received an X and a Y (XY) , would it grow into a male or a female? u 4. female, o -s male :l' *) { S. With the above information, you can verify why all populations of plants and animals have close to 50% males and 50% females. (Remember: when sperm cells are formed, the 2 chromosomes in a pair separate and go into different sperm cells.) What chromosome would you find in each of 2 sperm cells formed? What chromosome would be found in each egg cell? Ch 34 Chromosomss, Genes and lnheritance 5. X or Y in male sperm cells and X only in all of the lemale eggs. 6. Now you can create a Punnett square to determine which chromosomes will end up together in all possible offspring: Copy this chart on to your own paper and complete it. What fraction of the offspring are males? What fraction females? eggs b. spe rm XI Y 112 male and 112 female 7. Remember that the X and Y chromosomes are called "sex" chromosomes. Tbe remaining 22 pairs of chromosomes are called "body" chromosomes. Geneticists call them autosomes. The pair of body chromosomes below show how the genes for eye color and height and other unidentified genes are arranged on the pair of chromosomes. B = brown-eye gene b = blue eye gene T = tallness gene t = shortness gene :-EE_: What color eyes would this person have and would he be tall or short? Notice that the genes for eye color are opposite each other on each chromosome and are at the same level. This is true for all gene pairs for any particular trait. Note that the genes for height are at the same level also. The other dark bands on the chromosomes represent other gene pairs at the same levels on each chromosome. Geneticists call gene pairs like this that are at the same levels, alleles. 7. Brown, tall Gh 34 Chromosomes, Genes and lnheritance 4r 8. The X and Y sex chromosomes present a unique situation since the Y chromosome is much shorter than the X. lt, therefore, cannot hold as many genes on it as the X can. This is very important to remember. +- Cobr blind gene q H X The diagram at the left will help you to understand this difference. Notice that the gene for color blindness is at the top of the X chromosome and that the Y chromosome is not long enough to hold a gene for this trait. Y The situation for the female is different since she has two X chromosomes. The diagrams below show all the possible combinations for the color blindness in males and females. Note that color blindness is a recessive trait (c) and that normal vision (C) is dominant. "H"H'H"f, XXXX normal visbn lemale normal vision {emale canier "Hl cH "H XY Hl XY normal cobrblind visbn male male "H"H XX cobr blind female Would you ever find a gene for color blindness on the Y chromosome? Explain why. A carrier is anv individual that carries a gene for a trait but does not exhibit the trait. 8. No. The Y chromosome is too short to have room at the same level for this gene. So REMEMBER, Y chromosomes are too short to carry either a color blind gene (c) or a normal vision gene (C), or any other sex-linked trait. 9. To solve color blindness inheritance problems, it's best to use symbols rather than drawing out chromosomes as done above. The above conditions are usually symbolized by showing the X and Y chromosomes and which gene is attached to the chromosome as follows: A normal vision female would be symbolized as XCXC and the normal vision male would be shown as XCY. How would you symbolize the following: Normal vision female carrier of color blindness? Color blind male? Color blind female? ' Ch 34 Chromosomes, Genes and lnheritance 44 9. XcXc xcY xcxc 10. You should now be able to solve a color blindness problem. Remember that anywhere the X goes, the attached gene goes with it. Also remember that the Y has no color blind or normal vision gene attached to it. Try the following problem: Cross a colorblind male with a female carrier of color blindness. First show the genotypes of the parents and then show the genotypes, phenotypes and fraetions of each kind of offspring. X Parents color blind carner List the genotypes and phenotypes of allthe offspring and state the fractions of each: xcY xc x' Of the females, 1/2 will be carriers and 112 color blind. For the males, 1/2 will be normal and 112 color blind. 10. 11. Muscular dystrophy is an inherited disease. The gene for it is recessive and it is sexlinked as in color blindness. Under these conditions, males will inherit the trait more often than females. This is because a male only needs to get the one recessive gene from his parents and he will have the disease. A female will have to get a recessive gene for the condition from BOTH parents in order to have the condition. This fact causes males to have sex-linked conditions 10 times more often than females. Muscular dystrophy is a condition that affects the muscles and causes weakness and muscle degeneration. The child that inherits M.D. eventually will not be able to move and usually dies by the time he becomes a teenager. There is no known cure. The disease usually begins to show up between the ages of 6 and 9. Write the genotypes for the following people: Male with Muscular dystrophy (M.D.) Male, unaffected bY M.D. Female with M.D. Female carrier of M.D. Unaffected female that is not a carrier Ch 34 Chromosomes, Genes and lnheritance 45 11. XmY xMY xmxm xMxm xMxM 12. Assume you are a genetic counselor and a couple comes to you for counseling. They want to know if there is any chance that their first baby might have muscular dystrophy. Neither of these two have M.D. but the wife's father has M.D. What would you advise them? Could any of their children have M.D.? Would any of the girls born have M.D.? Would any of the boys born to this couple have a chance of having M.D.? (Show your work on your own paper) 12. Begin by putting down what you know about the parents. (The man and wife) They are both normal. xMv x husband xMx? wife The wife has an M but the ? could be either an M or m. Her father had M.D. and that means he was XmY. Therefore the ? in the wife must be m. She would get the m as follows: XmY X father I XMXM mother I Y xmxM Fr wife Then this wife, when croised with her husband would pass on genes as determined using the Punnett square: XMY husband XMXm X wife The Punnett square will give 114 normal females (XMXM;, 1t4 lemale carriers (XMXm;, 114 normal males (XMY), and 1 /4 ol Jhe males with M.D. (XmY). You would, therefore, inform the couple that the chance that their first baby might have muscular dystrophy would be 114 or a 25"/" chance. Ch 34 Chromosomes, Genes and lnheritance 46 13. Hemophilia is a disease which is sex-linked. Those with the disease do not have normal clotting mechanisms in the blood which causes blood to clot when cut or bruised. This condition is inherited and until recently, was fatal to most of those who inherited it. The person with the disease usually died from bleeding to death from a small cut or bruise before becoming an adult. This trait is inherited by a recessive sex-linked gene in the same manner as the other sex-linked traits covered earlier. It is well known to historians that hemophilia was passed from generation to generation in the royal family of England. For example, in the 1800's, Queen Victoria and King Albert had a son, Prince Leopold who had' hemophilia. Neither the king nor the queen had hemophilia. What is Leopold's genotype and what are the genotypes of the king and queen? 13. XHXh Queen X * XHY Kins xtlY (Prince Leopold) 14. Since people have more than one sex-linked trait, the genotypes can become complicated in some problems. Consider the following: A color blind, hemophiliac husband (XchV1 and a color blind wife who does not have hemophilia (XcHlcH) have 4 children. Use the genotypes given and figure out the genotypes and phenotypes of each possible child. 14. The possible offspring are as follows: 1/2 color blind females carrying a gene for hemophilia (XchXcH;, 1/2 color blind males, normal for hemophilia (XcHV; BLOOD TYPE INHEHITANCE 15. Each person's blood type is inherited from parents. The four blood types are type A, type B, type AB and type O. Anytime blood is transfused form one person to another, blood type is checked to be sure the recipient's blood is compatible. Persons with type O blood can give blood to any other person. Those with type AB blood can receive blood from any other person. People can give blood to or receive blood from another with the same blood type. Ch 34 Chromosomes, Genes and lnheritance 47 Blood types are inherited as in hybrid crosses. To do blood type heredity problems, use the following genotypes: Blood Type I Genotype Type I AA. or AO Type I BB. or BO AB TypeAB A B I TypeO | @ Try the following cross. Cross a homozygous type A with a homozygous type B. 15. lA lA B IAFIAB B IABIAB All offspring will be type AB. 16. Cross a heterozygous type A with a heterozygous type B. What fraction of each blood type is possible in their offspring? 16. IA I O B IAB I BO o lAoloo Ch 34 Chromosomes, Genes and lnherilance 114 ol the children will be type AB, 114 type A, 114 B, and 114 type O. 48 34-4 Sample Sex-Linked and Blood Type Problems Obiectlve You are expected to be able to apply the principles of sex linkage and blood type genetics to solve the following problems. BLOOD TYPE 1. Put the work and answers on your own paper and circle all answers. Cross the following parents and show all the possible offspring: a. Type O type AB X (Homozygous) b. Type A Type B (heterozygous) X c. 2. PROBLEMS Type A (heterozygous) X Type O A type AB woman marries a man with type B whose mother was type their offspring would be expected to be type A? O. What % of SEX LINKED PROBLEMS: Show "/" of all phenotypes and all genotypes. Circle all answers. 3. Cross the following: a. Color blind man with a normal vision woman (not a carrier) b. Color blind man with a normal vision female carrier c. Color blind female with a normal vision male 4. Cross the following: a. A man with muscular dystrophy with a normal female carrier of muscular dystrophy b. A man with muscular dystrophy with a normal female whose father had muscular dystrophy 5. Cross a female hemophiliac with a normal man with no history of hemophilia in his family. Ch 34 Chromosomes, Genes and lnheritance 49 34-5 Sex-Linked and Blood Type Problem Set Objectlve You are expected to be able to apply the principles of sex linkage and blood group genetics to solve the following problems. BLOOD TYPE PROBLEMS 1. Put all work on your own paper and circle all answers. Two parents, both with type A blood, have a son with type O blood. What are the genotypes of both parents? 2. What To of any future children from the parents in problem 1 above would you expect to have type B blood? What 7" would have type A blood? 3. A man with type AB blood marries a woman with type A blood. The woman's genotype is not known in that it can be either homozygous or heterozygous. lf one particular genotype were to show up in their children, it would tell us the precise genotype of the mother. What is this blood typelgllhe3ttspdng that would allow us to determine the mother's genotype? Explain. B blood claimed that a certain J. R. Wilson, a multimillionaire oil tycoon, was the father of Mrs. Fleming's recent 4 month old baby. The Flemings took the issue to court charging that Mr. Wilson was the father and that he should pay $35,000.00 per year to the Wilsons for child support. Mr. Wilson's blood type is AB. The baby's blood type is type O. 4. Mr. and Mrs. Fleming, both with type (a) lf you were the expert genetics witness called into court by Mr. Wilson's attorney, how could you show that the baby could not be Mr. J. R. Wilson's? (b) ls it possible that the baby is actually Mr. Fleming's? Explain your answer. SEX LINKED TRAITS PROBLEMS: The problems that follow are typical of those that appear on the unit exam. lt's best if you show your work by diagramming the crosses. Write out both the genotypes and the phenotypes when asked to do so. CIRCLE the answer asked for in each problem. 5. A female carrier of color blindness married a normal vision man. What % of their children would you expect to be colorblind? have a boy and a girl with normal vision. The girl marries a normal vision man and their first son is colorblind. What are the genotypes of the Smiths? What are the genotypes of both the Smith children? 6. The Smiths, who both have normal vision, Ch 34 Chromosomes, Genes and lnheritance 50 7. The parents of a boy with hemophilia both have normal clotting blood. What is the genotype of the mother of this hemophiliac? 8. A normal vision man with muscular dystrophy, married a woman with normal vision and no symptoms of muscular dystrophy. The woman's father is colorblind and has muscular dystrophy. What l" of their children could be both colorblind and have muscular dystrophy? What % of their sons could you expect to have muscular dystrophy? 9. A blue eyed, colorblind, but otherwise normal man, married a hemophiliac wife with muscular dystrophy. (Poor couple) What % of their children would you expect to have hemophilia? Ch 34 Chromosomes, Genes and lnheritance 51