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OHAPTER 33 APPLYING THE PRINCIPLES OF GENETICS 33-1 Laboratory lnvestigation: Using Poker Chips to Understand Hybrid Grosses 33-2 A Programmed lntroduction to Genetics 33-3 lntroduction to Solving Hybrid Cross Problems 33-4 A Review of Hybrid Cross Problems 33-5 Hybrid Gross Problem Set Ch 33 fuplying the Principles of Genetics 13 Page 14 Page 21 Page 27 Page 31 Page 32 Cfropter 33 gppfuin7 tfte gincipfes af Qenetiu Wett dmu is fietter tfian weff soi[. Ben Franklin 33-1 Laboratory tnvestigation Using Poker Ghips to Understand Hybrid Crosses Objective By the end of this lab, you should be able to diagram a hybrid cross using the appropriate symbols for gene formulas. Manipulating the poker chips will help you understand how the genes are distributed to offspring lrom the parents. Work in groups of 2 at your table during that part of the lab when the poker chips are required. Then work individually on the programmed part of the lab. You may be given a quiz at the completion of the activity. You will find two containers on your table, one marked male, the other marked female. t I Each poker chip in the male container (14 colored, 14 white) represents a sperm cell. Each poker chip in the female container (14 colored, 14 white) represents .an egg cell. I I One person at the table should do Thoroughly mix up the chips in each container. pull out a chip from each container at the following: Without looking in the containers, the same time, and place them side-by-side on the table as a pair. Arrange the poker chips in pairs as shown on the next page. Keep doing this until all of the poker chips have been drawn from the containers.' Ch 33 Applying the Principles of Geneiics 14 @@ @ etc. 1. What does each chip in the female container represent? 1. An egg 2. The placing together of a poker chip from each container represents what process in (Remember what each chip represents.) living animals? 2. fertilization 3. Each pair of chips represents which of the following? a. sperm c. a zygote d. egg cells e. egg shells f. a winning bet ' 3. c. cells b. an embryo a zygote (or a new individual) or a iertilized egg. 1 4. Let C represent a colored chip and c represent a white chip. (You will see the reason for this shortly) Each container had 14 C's and.14 c's. What was your chance of drawing a C from eithei container? Express your answer as a fraction. Ch 33 Applying the Principles ol Genetics 15 4. 1tz 5. What was your chance 5. 6. of drawing a c from either container? 1t2 What was your chance of drawing a G irom the male container and a C from the female container at the same time? 6. 1i+ (Second law of Probability' 12X1rz =1r4\ is the chance of drawing a c from the male container and a c from the female container at the same time? 7. What ' 7. 114 (tnxlrz= v+) This is the chance of ge,tting an offspring with the gene formula cc. ) L What is the chance of getting a C from the male container and a c from the female container at the same time? 8. 1t4 (tzchance of getting cxtn=tn) 9. What Ch 33 is the chance of getting the pair Cc in any manner what-so-ever? Applying the Principles ol Genetics 16 9. 112eX112c=114Cc 1l2cX1l2C=1l4cC 114 Cc + 114 cC = 112 Cc Create a chart like the one below and fill in the columns based upon the results you obtained with the chips. Also place your data on the board for your table. Possible pair combinations Use symbols Number of times each combination occurred at your table What frac-tion of total pairs is this? What percentage? Percentage expected but probably not obtained Check to see if your calculations for "/" are correct. The following is a review on % calculation: Example: What percent is 8 out of a total of 30? This can be expressed as 8/30. To obtain o/" lrom a fraction, divide the denominator into the numerator. Then multiply by 100. ( I + 30 = .266, .266 X 100 = 26.6 %) Did you calculate all percent values in the chart in similar manner? 10. Place your team's results in the class results chart on the chalk board. t-l After all teams have placed their data on the chalk board, answer the next question. (While waiting, you might need to go on reading and come back to this question.) What is the average "/" lor each category for your class? '10. The percentages will vary with each class. Copy them from the board for #10. '11. Which set of percentages, the class averages or your team's data, comes closest to 25"/" lor each category? Ch 33 Applying the Principles of Genetics 17 11. The class average l" dala usually comes closer lo 25h for each category. On rarer occasions, the team data is closer. 12. Why is the class average data usually closer than the team data is to the expected 25Y" lor each category? 12. The greater the sample size, (number of cases) the greater the accuracy of the data and the greater the chance is for the data to come closer to the expected results. 13. Review: Each container of chips represented a parent. One is female and one is male. Each parent has two kinds of genes. PlCcXCc Each parent can contribute one kind of gene or the other. NOT BOTH. What is the This is illustrated by picking a poker chance that the male will contribute a C? chip out of the container marked male. What was the chance that the female could Placing the two poker chips together as a pair on the table contribute a C? represents fertilization and the formation of a new individual with the gene combination of CC (gene formula) The chance of obtaining this offspring is 1/4. - 13. 1t2, 112 14. An alternate way to show what happens is to use a method called the Punnett placed The at of chart. the top the are female Square. The eggs possible from the possible sperm cells are placed along the side of the chart. Next the eggs and sperm.are combined in the 4 boxes to show the 4 different possible offspring and the fractions of each according the Second Law of Probability. This is done as follows: \-t-,.Ch 33 Applying the Principles of Genetics '18 Parents (P 1 ) X Cc (male) Cc (female) lf C represents a factor for colored fur in mice and c represents a factor for white fur, what fraction of the offspring from parents Cc X Cc would you expect to have colored fur? 14. 114 CC + 1/2 Cc = 3/4 with colored fur. (C is dominant over c) 15. What fraction of the offspring in cross Cc x Cc would you expect to have white fur? 15. 114 cc with white fur 16. lf we would expect offspring with gene pairs determined above and 1/4 cc), then why did you not get 25"/" CC', 50% Cb and CC, 1t2 Cc 25Y" cc with your poker chips? 16. Your poker chip percentages were not quite 25V", sOV", 25Y" because the percentages are only. Experimental results usually come close but are not exactly those EXPECTED percentages. The actual experimental results are affected by chance and will usually vary from of examples are used, the expected comes closer to the actual results obtained: the EXPECTED. When large numbers Please return the poker chips to the appropriate containers. Put 14 colored and 14 white in each container. 1 t Ch 33 Applying the Principles of Genetics 19 (1/4 17. lf you have understood the previous example for a genetic cross when poker chips were used to visualize the distribution and recombination of genes, then you should be able to solve the following sample test question: ln certain dogs, dark color (D) is dominant to light color (d). Ddx What color is each of the parents in the above cross? 17. 18. Both are dark in color. Determine the gene formulas, appearances and the fractions of each for the offspring using a Punnett Square. 18. 1/4DD + 1l2Dd + 3/4 dark + 1/4 light ll4dd 19. This next sample question is a little different. One parent is light and the other dark. :tDdxdd Determine the gene formulas, appearances of otfspring andthe fractions of each. 19. Parents (P 1 ) Dd (male) or llzDd + 1l2dd (1/2dark+ 1/2 light) Ch 33 Applying the Principles ol Genetics 2A X dd (female) is 20. ln the following crosses, C = colored fur and c = white fur. List allthe possible gene formulas and appearances for offspring for the following crosses. What fraction of each appearance is obtained? Cross CC Xcc Cross CcXcc ccXcc Cc XCc Cross Cross Check the resuhs wilh the others at your table. 21. ln pea plants, tall plant genes are dominant to short plant genes. Cross a tall pea plant (carrying a gene for shortness) with a short plant. What fraction of the offspring will be tall and what fraction short? Check the results with the others at your table. 33-2 A Programmed lntroduction to Genetics Obiective On a quiz that follows this program, you should be able to diagram a hybrid cross using the appropriate symbols for gene formulas. Also be able to state definitions for dominant, recessive, genotype, phenotype, homozygous and heterozygous. Animals and plants possess a great variety of traits. Humans have various hair and eye color, size, etc. Plants can be tall or short, have red, yellow or white flowers, etc. A guinea pig can have white or brown fur which can be long, short or curly. All of these TRAITS express how the individual looks or appears to you. GENETICS is the study of how these hereditary traits are passed on from one generation to another. lt is a fascinating study and one that will enable you to understand how you may have inherited certain hereditary characteristics you possess. You will also understand how traits you have would be passed on to your offspring and future generations. When you have completed this program you will understand the meanings of basic Ch 33 Applying the Principles ol Genetics 21 genetics terms and the ways in which plants, animals or people are symbolized to show their genetic make-up. Write your answers on a separate sheet of paper. Use the paper to cover the answers as you progress through the program. 1. Write the definition for GENETICS presented earlier without looking back. 1. GENETICS is the study of how hereditary traits are passed from one generation to the next. 2. List each of the traits mentioned in the first paragraph in this topic. 2. Hair, eye color and size for humans; tall, short, red flowers, yellow flowers, white flowers for plants; white or brown fur, long, short or curly fur for guinea pigs. 3. List some specific genetic traits that you possess. 3. . Answers will vary (you might have listed specific hair and eye color, straight or curly hair, size, complexion or race, facial and body features. 4. BASIC CONCEPT NUMBER ONE: EACH ONE TRAIT is determined by TWO GENES. The genes are on chromosomes inside of the nucleus of each one of your cells. You will learn more about this later. lf a person has blue eyes, how many genes would be needed to produce blue eyes? 4. Two 5. lf a geranium plant was a special short variety and produced only red flowers, how many genes would that plant possess for those two traits? 5. Four (2tor height and2forflowercolor) Ch 33 Applying the Principles of Genetics 22 6. A person has blond curly hair and blue eyes. How many genes would be needed to produce these traits? 6. Six genes (2 lor hair color, 2 tor hair curliness and 2 for eye color) 7. ln order to figure out how traits are passed from generation to generation, it's convenient to use symbols to represent traits. For example, tallness in plants is represented with a T, red flowers with an R and brown eyes with a B. The gene for shortness is represented by a t and not an S or s. The gene for white flowers is r and blue eyes is b. Fill in the symbols for the traits below: Height Flower Color Tall Red Short White 7. T Eye Color Brown Blue r t R B White Brown Blue b Red Short that the first letter of the dominant gene is always used and is made the capital letter. lf short is dominant over tall, short would be symbolized as S and tall as s. Tall *Note 8. Since each trait is represented by 2 genes, a tall plant would be represented as TT and a short plant as tt. The observed appearance of a trait is called its PHENOTYPE. The symbolized form. or gene formula for that trait is called its GENOTYPE. Write the genotype and phenotype for a tall plant. 8. TT tall or Tt tall 9. What is the genotype of a brown eyed person? What is the phenotype of a short plant? What is the genotype of a short plant? 9. A brown eyed person could be BB or Bb The phenotype of a short plant = short The genotype of a short plant = tt Ch 33 Applying the Principles of Genelics 23 10. When a tall pea plant is crossed with a short pea plant, all the offspring are always tall. This means that tallness is DOMINANT over shortness. Shortness is said to be a RECESSIVE trait. This is the reason geneticist use capital letters to represent DOMINANT traits and lower case letters to represent RECESSIVE traits. Which is the dominant flower color, red or white? Which eye color, blue or brown, is the dominant trait? Which eye color is RECESSIVE? 10. Red, Brown, Blue 11. Are dominant traits symbolized with capital or lower case letters? Are recessive traits symbolized by capital or lower case letters? The letter selected as the symbol always comes from which trait - dominant or recessive? 11. Capital, lower case, dominant ... TT x tt all the offsprings are tall. Remembering that each parent contributes genetic material to the offspring, what would you predict to be the genotype of these tall 12.11a tall plant is crossed with a short plant offspring? 12. Tt 13. Note that this new plant has a gene for tallness and a gene for shortness. The fact that the plant is tall illustrates the principle of dominance. The t gene for shortness is dominated by the presence of the T gene for tallness and shortness is not expressed. lf a brown eyed person BB is crossed with a blue eyed person bb, what would the genotype of the offspring be? What would the phenotype be? 13. Ch 33 Bb, brown Applying the Principles ol Genetics 24 14. Crosses are often diagrammed as follows: X Red flowered pea plant (male) Both genes dominant White llowered pea plant (female) t Offspring What are the genotypes for the 2 parent plants above? RR 14. (male), rr (female) 15. What would the genotype and phenotype of the ofispring from the above cross be? 15. Rr, red 16. Two terms are routinely used by geneticists to distinguish between the 2 ditferent types of genotypes. Notice that a genotype can have the same genes in the pair: TT, tt, or RR, rr. This kind of genotype is called a HOMOZYGOUS genotype. Homo means "same" and zygous means "in the zygote", therefore HOMOZYGOUS means the 2 genes in the zygote are the same. Also note that the 2 genes in the This condition is called zygote can be different, as with Tt, Rr, or HETEROZYGOUS. Hetero means different. lndicate whether each of the following genotypes are homozygous or heterozygous: FB, Hr, rr, Aa, YY, DD Bb. 16. homozygous heterozygous homozygous heterozygous homozygous homozygous "Also note that a brown eyed person can be either BB or Bb 17. ln review, and without looking back, see if you can define the 6 terms presented in HETEROZYGOUS this program. GENOTYPE PHENOTYPE HOMOZYGOUS DOMINANT RECESSIVE Ch 33 Applying the Principles of Genetics 25 17. GENOTYPE - The gene formula of an individual PHENOTYPE - The observed appearance of an individual HOMOZYGOUS - When both genes of a genotype are the same HETEROZYGOUS - When lhe 2 genes of a genotype are different DOMINANT - The gene of the pair that dominates over the other and its trait is expressed. (Symbolized with capital letter) RECESSIVE - The gene that does not express itself when paired with a dominant gene. (Symbolized with lower case letter) R EVI EW 18. See if you can apply these definitions to the following statements: When we notice a person's blue eyes, we are noticing his (genotype or phenotype). How is a blue eyed person symbolized? When one symbolizes a trait, what it is called? This genotype for blue eyes is (homozygous or heterozygous)? The symbols show which eye color is dominant and which eye color is recessive. 18. Phenotype, bb, genotype, homozYgous, brown, blue 1g. See if you can assign symbols for genotypes according to the principles learned' When an animal with curly hair is crossed with an animal with straight hair, all the offspring are curly haired. The curly-haired parent would appropriately be The symboliied as _ and the straight-haired parent would be symbolized as hair. Which and would have oifspring would be symbolized as -. trait is dominant? - 19. CC, cc, Cc, curlY, curlY 20. On the quiz that follows, you should be able to apply these definitions to questions on the quiz. Review to prepare for the quiz on this programmed topic. Ch 33 Applying the Principles of Genetics zo 33-3 lntroduction to Solving Hybrid Cross Problems Ob jective You will be expected to be able to solve hybrid cross genetics problems by using the "Punnett Square." Place all answers on your own paper. Cover the answers as you go. 1. Two parents have brown eyes and also carry genes for blue eyes. Brown eyes (B) are usually dominant over blue (b) eyes. What is the genotype of a person that is homozygous for brown eyes? What is the genotype of a person who is homozygous for blue eyes? What is the genotype of a person who is heterozygous for brown eyes but carries a gene of blue eyes? 1. BB, bb, Bb 2. Now examine a cross between two parents who are heterozygous for brown eyes. The cross can be written as follows: BbXBbPl The P1 indicates the "1st parents." The "first offspring" are referred to as the F1 generation. The "second offspring" or grandchildren of the P1 are called the F2 generation. eggs To determine the F1 offspring, a box called the Punnett Square can be used. lt's one of the simplest ways to solve this type b of B problem. square, To determine the offspring square by one simply moves the gene found above and the one found to the left of the square into the box to create pairs of genes. sperm b When this is done for the left side, the sQuare will appear as follows: Ch 33 Applying the Principles of Genetics 27 eggs Copy this square onto your own paper and fill in the right side of the square using the same technique. sperm eggs BI 2. BB Bb Bb bb Now indicate what eye color each of the four offspring will have. sperm b 2. 3. BB = 112 What fraction of the blue eyes? 4. Ch Bb - Brown, bb = blue Remember that when sperm cells are formed, only one gene of the pair can go into a sperm cell. According to the laws of chance that you demonstrated with coins, cards and dice, What fraction of the sperm will carry the B gene? What fraction will carry the b gene? 3. 4. Brown, 33 Fl B and 112 b offspring would have brown eyes? What fraction would have 3/4 brown eyes and 1/4 blue These are called the PhenotYPe fractions or ratios. Applying the Principles o{ Genetics 28 5. What are the fractions lor each genotype? 5. 114 BB, 1l2Bb, l14bb (These are called the genotypic ratios) 6. Determine the offspring for the following cross using the Punnett Square method: BbXbbPl 6.bb 'l "_1" | " ol un lon I 7. What are the phenotypic and genotypic ratios for the F1 offspring? . 7. Phenotypic ratios = 112 brown + 1/2 blue eyed Genotypic ratios =112 Bb + 1l2bb 8. Apply what you have learned to this next problem. ln pea plants, tall plants (T) are dominant over short plants {t). Cross the following to determine the F1 offspring: (Give the phenotypes, genotypes & lractions of each.) fixttP1 8. all Tt (100% tall) 9. Now cross the F1 with itself. (Tt X Tt ) This is called an F1 cross. (Give the phenotypes, genotypes & fractions of each for the F2.) Ch 33 Applying the Principles of Genetics 29 9.314 tall + 1/4 short 114Tl + 112 Tt + 1/4 tt 10. lf 40 seeds were planted from the above cross, how many tall plants would grow? How many short plants? 10. 30 tall and 10 short Plants 11. ln pea plants, round seeds are dominant over wrinkled seeds. Cross a heterozygous round seeded plant with wrinkled seeded plant. Assign the symbols and determine the genotype and phenotypes of the F1 offspring. 11. The cross would be: Br X rr The F1 offspring would be 112 round (Rr) and 1/2 wrinkled (rr) Ch 33 Applying the Principles of Genetics 30 33-4 A Review of Hybrid Cross Problems Objectlve You will be expected to apply the principles of solving hybrid crosses to the problems that follow. Work out the following problems on your own paper. Show all your work for each problem. Circle the final answer or answers. No late papers will be accepted after the answers have been given in class... 1. Usually, but not always, human eye color is inherited as if brown eyes were dominant and blue eyes were recessive. Assume that this is correct for this problem and any others in this unit. (B= brown, b=blue) A blue-eyed mother bb is married to a brown-eyed man (heterozygous Bb). What is the chance that their lirst child will be blue-eyed? Brown-eyed? (Use the Punnett square method you learned in topic 33-3) 2. A tall pea plant (Tt) is crossed with a short pea plant (tt). What fraction of their offspring would you expect to be tall? Note that tall is dominant and shortness is recessive. (Use the square method) 3. Cross a white guinea pig Ww with another white guinea pig Ww. Both parents carry a gene for blackness (w) which is not expressed. ln other words, both are heterozygous. Use the square method and answer the following: 3 a. What fraction of the F1 offspring will be white? What % white? 3 b. What fraction will be black? What %? 3 c. What fraction of each genotype will you get? What % of each genotype? 3 d. What fraction of each phenotype wilt you get? 4. ln shorthorn cattle, some are red, some are white and others are roan. Roan is close to pink in color. Neither red nor white is dominant. For this reason, the symbols used to represent these animals are generally different. Use the following genotypes to work out the problems that follow: Neither red nor white is dominant. Cross a red cow with a white bull. Give the fraction and each color of offspring possible from this mating. 5. Cross a roan bull with a white cow. Give the colors and fractions for all possible otfspring. Before handing in your work, re-read the instructions at the beginning of this topic and be sure you followed them exactly. Be sure you circled all of your answers. Ch 33 Applying the Principles of Genetics 31 33-5 Hybrid Cross Problem Set Objectlve You will be expected to apply the principles of solving hybrid crosses to the problems that follow. Answer the following on your own paper. Show your work or give an explanation for your answer. Present all work NEATLY. 1. Show all the possible genotypes from the following crosses: (indicate the fractions of each genotype) Gg XGg Gg xgg 2. lf G in the above problem is green apples and g is red apples, what would the fractions of each phenotype be in the two crosses in the above problem? 3. A brown-eyed mother and a blue-eyed father found that their first child was blueeyed. What is the genotype of the mother? (The exact genotype) 4. What is the 7" chance that the couple in problem #3 would have a second child that has brown eyes? 5. ln cats, assume that a spotted coat is dominant to a white coat. A white mother cat gives birth to two white kittens and two spotted kittens. What are the genotypes and phenotypes of the father cat? 6. A man with blue eyes marries a brown-eyed woman whose mother had blue eyes. What portion of the children would be expected to have blue eyes? Show the genotypes of all people involved. CIRCLE Ch 33 all answers on your paper. Applying the Principles of Genetics 32