Genetic Variations. F1 Generation. Mechanisms of Genetics W W. STAAR Biology: Assessment Activities

Transcription

1 male parent female parent sperm cells egg cells F1 Generation Mechanisms of Genetics 181

2 182

3 Mechanisms of Genetics Teacher Pages Purpose The purpose of this activity is to reinforce students understanding of the significance of genetics; the possible outcomes of monohybrid, X-linked, and dihybrid genetic crosses; and the limitations of models. Correlations to the Texas Essential Knoledge and Skills Note: Text ith a line through it indicates this part of the TEKS is not being addressed in this activity. Some TEKS statements printed here end ith a semicolon or the ord and ith nothing thereafter this indicates that further TEKS statements follo but are not included here. (6) Science concepts. The student knos the mechanisms of genetics, including the role of nucleic acids and the principles of Mendelian Genetics. The student is expected to: (F) predict possible outcomes of various genetic combinations such as monohybrid crosses, dihybrid crosses and non-mendelian inheritance; (Readiness standard) (2) Scientific processes. The student uses scientific methods and equipment during laboratory and field investigations. The student is expected to: (G) (H) analyze, evaluate, make inferences, and predict trends from data; and (Incorporated) communicate valid conclusions supported by the data through methods such as lab reports, labeled draings, graphic organizers, journals, summaries, oral reports, and technology-based reports. (Incorporated) (3) Scientific processes. The student uses critical thinking, scientific reasoning, and problem solving to make informed decisions ithin and outside the classroom. The student is expected to: (E) evaluate models according to their limitations in representing biological objects or events; and (Incorporated) Materials Chenille sticks (12 black, 3 gray, 17 bron) Beads sized to slip snugly onto the chenille sticks (3 purple, 10 black, 10 blue, 2 yello, 2 bron, 2 hite, 1 red, 1 clear) Glue Resealable plastic bags (3) Note: The colors specified for the chenille sticks and beads are simply suggestions; you do not need to find these specific colors. You just need three different colors of chenille sticks and eight different colors of beads. Teacher Pages 183

4 STAAR Biology: Assessment Activities The folloing materials are included in the blackline masters for this station, hich are available in color on the enclosed DVD. Station Information sheet Student Pages Supplementary Resources Basic Principles of Genetics: Exceptions to Simple Inheritance. Retrieved on May 18, 2011 from the ebsite of the Behavioral Sciences Department at Palomar College: palomar.edu/mendel/mendel_3.htm. Advance Preparation 1. Print one copy of all the blackline masters for this station from the enclosed DVD using a color printer color is essential to the station activities. Make one copy of the Student Pages (including the glossary) for each student. 2. In this activity, chenille sticks of different colors and lengths are used to represent chromosomes. Different colored beads are placed on the chenille sticks to represent genes that signal specific traits. 3. Begin by preparing the chenille sticks. Use the table belo to guide you in cutting the various lengths. Chenille Stick Cutting Guide color length number needed black 24 cm 4 black 12 cm 4 black 8 cm 4 gray 20 cm 3 bron 10 cm 1 bron 12 cm total 4. Once the sticks are cut to the correct lengths, bend each chenille stick in half and tist the ends together, as shon belo. This better represents the tisting appearance of chromosomes. Doubled and tisted chenille stick 184 Teacher Pages

5 5. Next add the beads to the chenille sticks. You may need to partially untist the sticks to put the beads in the proper place. The beads should fit snugly onto the sticks, but they should be secured in the proper place ith glue. Use the chart belo to guide you in placing the beads on the chenille sticks. Bead Placement Guide chenille stick number of sticks bead color bead placement 24-cm black 2 black 10 cm from one end 24-cm black 2 blue 10 cm from one end 8-cm black 3 purple middle 8-cm black 1 clear middle 12-cm black 2 yello middle 12-cm black 2 bron middle 20-cm gray 2 hite 8 cm from one end 20-cm gray 1 red 8 cm from one end 10-cm bron 1 no bead cm bron 8 blue 3 cm from one end 12-cm bron 8 black 3 cm from one end 6. Take one of the plastic bags and label it Female Chromosomes. Put the folloing eight chenille sticks in it: 24-cm black stick ith black bead (1) 24-cm black stick ith blue bead (1) 12-cm black stick ith yello bead (1) 12-cm black stick ith bron bead (1) 8-cm black stick ith purple bead (1) 8-cm black stick ith clear bead (1) 20-cm gray sticks ith hite beads (2) Teacher Pages 185

6 STAAR Biology: Assessment Activities 7. Label the second plastic bag Male Chromosomes. Put the folloing eight chenille sticks in it: 24-cm black stick ith black bead (1) 24-cm black stick ith blue bead (1) 12-cm black stick ith yello bead (1) 12-cm black stick ith bron bead (1) 8-cm black stick ith purple bead (2) 20-cm gray stick ith red bead (1) 5-cm bron stick, no bead (1) 8. Label the third plastic bag ing Type Chromosomes. Put the folloing 16 chenille sticks in it: Station Setup 12-cm bron stick ith blue bead (8) 12-cm bron stick ith black bead (8) 1. Laminate a copy of the Station Information sheet and tape it onto the station table. Students ill use this to confirm that the station is set up correctly. 2. Place the three plastic bags containing the beaded chenille sticks at the station table. Procedures 1. Tell students to check the station setup against the Station Information sheet hen they arrive at the table. If anything is missing or out of place, they should notify you. 2. Pass out a copy of the Student Pages to each student. Instruct students to ork through the procedures and anser the questions ith their teammate(s). 3. As students ork through the station activity, circulate around the room, checking their ork and responding to questions. 186 Teacher Pages

7 Guide to Student Responses Note: The suggested student responses presented belo in italics represent the best possible ansers to the student questions; actual student responses may vary. Essential Question Hemophilia is a sex-linked trait that is carried on the X chromosome. hy is there a higher probability that males ill exhibit the characteristics of hemophilia than females? Hemophilia is a disease, carried only on the X chromosome in humans, that prevents blood from clotting properly. Males have one X and one Y sex chromosome, so the hemophilia gene can appear on only one chromosome in males but males need only one hemophilia gene to exhibit the characteristics of the disease. Females have to X chromosomes and thus have an increased chance of carrying the gene on one of the chromosomes. Hoever, the gene must be present on both X chromosomes in order for females to exhibit the characteristics of hemophilia. Therefore, males are more likely than females to exhibit the characteristics of hemophilia. Activities and Questions 1. Identify the genotype and phenotype for each pair of alleles on the male chromosomes. Male Homologous Chromosomes Genotype Y X R B B Y y Phenotype red eyes normal ings normal bristles yello body color Teacher Pages 187

8 STAAR Biology: Assessment Activities 2. Identify the genotype and phenotype for each pair of alleles on the female chromosomes. Female Homologous Chromosomes Genotype X r X r B b Y y Phenotype hite eyes normal ings normal bristles yello body color 3. From the diagram belo, select the to male chromosomes that represent a parent ho is heterozygous for normal ings. Next, select the to female chromosomes that represent a parent ho is heterozygous for normal ings. A or C or B or D or 188 Teacher Pages

9 hich set of sex cells (A or B) ould best represent the female traits? hich set of sex cells (C or D) ould best represent the male traits? The correct anser is A for females and D for males. The egg cell A and the sperm cell D each contain to chromosomes, one ith the dominant gene () represented by the blue bead and the other ith the recessive gene () represented by the black bead. This condition is heterozygous () for normal ings. 4. Locate the Genetic Cross Flochart and the plastic bag labeled ing Type Chromosome. Carefully remove the chromosomes from the envelope and arrange them on the flochart to represent ho the chromosomes ould appear in the cross from Question 3. Genetic Cross Flochart male parent female parent sperm cells egg cells F 1 Generation Teacher Pages 189

10 STAAR Biology: Assessment Activities Indicate the letter of the trait on each chromosome on the flochart belo. Use arros to indicate hich sperm cell and egg cell come together to produce an offspring. Genetic Cross Flochart male parent female parent sperm cells egg cells F 1 Generation Note that this model does not accurately represent the randomness that determines hich sperm cell may combine ith an egg cell to form an offspring. The example shos to sperm cells, but in reality a male parent produces hundreds of thousands of sperm cells. The example also shos only one order in hich the male and female sex cells could occur hen fertilization takes place. Make sure that students understand that the model presents a simplified vie of the process that occurs hen the to parents create offspring. 5. hat is the phenotypic ratio of the F 1 generation resulting from the previous cross? Support your anser ith data from the genetic cross. The phenotypic ratio is 3 to 1: 75% of the offspring ill have normal ings (), and 25% of the offspring ill be ingless (). Remind students that fruit flies hose genotype is or have normal ings, since in both cases they carry the dominant gene for normal ings. Only flies ith are ingless, since both genes are recessive and call for a ingless condition. 190 Teacher Pages

11 6. Eye color in fruit flies is an X linked (sex-linked) trait and is carried on the X chromosome only. A cross beteen to fruit flies results in 100 fruit fly offspring of hich: ¼ of the offspring are hite-eyed males ¼ of the offspring are red-eyed males ¼ of the offspring are hite-eyed females ¼ of the offspring are red-eyed females. hat must the parent genotypes be to produce this F 1 generation? Sho your ork in the Punnett Square belo to support the results of the cross. Female genotype = X r X R ; male genotype = X r Y. X r Y X r X r X r X r Y X R X R X r X R Y Note that the Punnett Square may lead students to develop the misconception that in all monohybrid crosses, four offspring are alays produced each time organisms reproduce. Teacher Pages 191

12 STAAR Biology: Assessment Activities 7. Complete the folloing cross to sho the genotypes of the missing offspring. bx R by BX R BY bx r bx r bx R bbx R X r bbx r Y BbX R X r BbX r Y bbx R X r bbx r Y BbX R X r BbX r Y bbx R X R bbx R Y BbX R X R BbX R Y Key to the Traits X R = Red eyes X r = hite eyes Y = Male chromosome B = Normal ings b = ingless bx R bbx R X R bbx R Y BbX R X R BbX R Y 8. Given the results from the dihybrid cross above, predict ho many of the offspring ill be male fruit flies ith red eyes and ingless bodies. hat are the phenotypes of the female offspring? The dihybrid cross indicates that to of the offspring ill be red-eyed ingless males. The female phenotypes are red eyes ith normal ings (4) and red eyes ithout ings (4). 9. The chenille sticks ith colored beads represent the four fruit fly chromosomes. hat are some limitations of these models? These models do not sho much detail. For example, the models don t sho hat an actual gene looks like, the tisting of the chromosome, and the actual location of the gene on the chromosome. In addition, non-mendelian traits are controlled by more than one gene, and these models don t represent such traits. 192 Teacher Pages

13 I need to be able to... Analyze and make inferences about dominant and recessive traits. Interpret and make predictions about genotypes and phenotypes. Determine and interpret phenotypic ratios. Understand the difference beteen Mendelian and non-mendelian traits. Use Punnett squares and other models to predict the results of genetic crosses involving X-linked traits. Interpret results and make predictions from monohybrid and dihybrid crosses. Evaluate the limitations of biological models. Teacher Pages 193

14 STAAR Biology: Assessment Activities 194 Teacher Pages

15 Mechanisms of Genetics Blackline Masters Contents Station Information sheet Genetic Cross Flochart Student Pages Blackline Masters 195

16 STAAR Biology: Assessment Activities KEY for Fruit Fly Traits Station Information: Genes (colored beads) blue = normal ings gene (colored bead) black = ingless X r X R B hite = hite eyes red = red eyes purple = normal bristles chromosome (chenille stick) Female b Y clear = fe short bristles yello = yello body color Autosome Sex chromosomes Y X y bron = bron body color (black) (bron) (gray) Genetic Cross Flochart Male male parent female parent Fruit Fly Chromosomes sperm cells egg cells F 1 Generation ing Type Chromosomes KEY = ingless = normal ings 196 Blackline Masters

17 Genetic Cross Flochart male parent female parent sperm cells egg cells F 1 Generation KEY = normal ings = ingless Blackline Masters 197

18 STAAR Biology: Assessment Activities 198 Blackline Masters

19 Mechanisms of Genetics Student Pages Purpose The purpose of this station is to reinforce your understanding of the significance of genetics; the possible outcomes of monohybrid, X-linked, and dihybrid genetic crosses; and the limitations of models. Before You Begin... Check to see that all the items are present and organized according to the Station Information sheet. If you notice a problem, notify the teacher immediately. Materials Station Information sheet Plastic bags (3), labeled Female Chromosomes, Male Chromosomes, and ing Type Chromosomes Genetic Cross Flochart Activities and Questions Essential Question Hemophilia is a sex-linked trait that is carried on the X chromosome. hy is there a higher probability that males ill exhibit the characteristics of hemophilia than females? Discuss the essential question ith your teammate(s) and record your anser in the space belo. Student Pages 199

20 STAAR Biology: Assessment Activities Locate the plastic bag labeled Male Chromosomes and the bag labeled Female Chromosomes. The chenille sticks in these bags represent male and female fruit fly chromosomes. Male Female Carefully remove the contents of each bag, taking care to keep the contents of each bag separate. Use the key belo to determine hich trait is expressed by the alleles found on the homologous chromosomes. KEY X r X R Genes (colored beads) blue = normal ings black = ingless hite = hite eyes red = red eyes chromosome (chenille stick) gene (colored bead) B purple = normal bristles b Y clear = fe short bristles yello = yello body color Autosome Sex chromosomes Y X y bron = bron body color (black) (bron) (gray) 200 Student Pages

21 1. Identify the genotype and phenotype for each pair of alleles on the male chromosomes. Male Homologous Chromosomes Genotype Phenotype body color bristles ings eye color 2. Identify the genotype and phenotype for each pair of alleles on the female chromosomes. Female Homologous Chromosomes Genotype Phenotype body color bristles ings eye color Student Pages 201

22 STAAR Biology: Assessment Activities 3. From the diagram belo, select the to male chromosomes that represent a parent ho is heterozygous for normal ings. Next, select the to female chromosomes that represent a parent ho is heterozygous for normal ings. hich set of sex cells (A or B) ould best represent the female traits? hich set of sex cells (C or D) ould best represent the male traits? A or C or B or D or Return the chromosomes to their envelopes, being careful to keep the male and female chromosomes separate. 202 Student Pages

23 4. Locate the Genetic Cross Flochart and the plastic bag labeled ing Type Chromosomes. Carefully remove the chromosomes from the envelope and arrange them on the flochart to represent ho the chromosomes ould appear in the cross from Question 3. Indicate on the flochart belo the letter of the trait on each chromosome. Use arros to indicate hich sperm cell and egg cell come together to produce an offspring. Genetic Cross Flochart male parent female parent sperm cells egg cells F 1 Generation KEY = normal ings = ingless Student Pages 203

24 STAAR Biology: Assessment Activities 5. hat is the phenotypic ratio of the F 1 generation resulting from the previous cross? Support your anser ith data from the genetic cross. 6. Eye color in fruit flies is an X linked (sex-linked) trait and is carried on the X chromosome only. A cross beteen to fruit flies results in 100 fruit fly offspring of hich: ¼ of the offspring are hite-eyed males ¼ of the offspring are red-eyed males ¼ of the offspring are hite-eyed females ¼ of the offspring are red-eyed females. hat must the parent genotypes be to produce this F 1 generation? Sho your ork in the Punnett Square belo to support the results of the cross. 204 Student Pages

25 7. Complete the folloing cross to sho the genotypes of the missing offspring. bx R by BX R BY bx r bbx R X r bbx r Y BbX R X r bx r bx R bbx R X r bbx r Y BbX r Y bbx R X R BbX R X R BbX R Y Key to the Traits X R = Red eyes X r = hite eyes Y = B = b = Male chromosome Normal ings ingless bx R bbx R Y BbX R X R BbX R Y 8. Given the results from the dihybrid cross above, predict ho many of the offspring ill be male fruit flies ith red eyes and ingless bodies. hat are the phenotypes of the female offspring? 9. The chenille sticks ith colored beads represent the four fruit fly chromosomes. hat are some limitations of these models? Student Pages 205

26 STAAR Biology: Assessment Activities 10. No that you have completed these questions, return to the essential question. ould you like to modify or change your anser? rite any modifications to your anser belo. Note: Because other students are going to do the activity after you, be sure to put all the materials at the station back as you found them. Sometimes there ill be materials that need to be reneed or replaced. If you need assistance or have any questions, ask your teacher. 206 Student Pages

27 I Need to Be Able to... Complete this part after class discussion of this station. I need to be able to... Student Pages 207

28 STAAR Biology: Assessment Activities Glossary Gene Genes are the parts of a chromosome that determine a specific trait of an organism. Allele An allele is a specific form of a gene. For example, a particular gene may control an organism s height tall or short. The allele is the form of the gene that specifically determines one of these conditions that its, one allele for the height gene determines that the organism ill be short. The other allele determines that the organism ill be tall. Likeise, an allele of the gene for eye color determines bron eyes. Dominant An allele is considered dominant hen it hides or masks other alleles. Recessive An allele is considered recessive hen it can be expressed only if no other allele for that trait is present. Homologous chromosome Homologous chromosomes are pairs of chromosomes of the same length ith genes for the same characteristics at corresponding loci. One homologous chromosome is inherited from the female parent, the other from the male parent. Genotype The genotype for an organism is represented by the actual alleles of a trait for example, Bb. Phenotype The phenotype of an organism is the actual physical expression of the alleles for example, bron hair. Monohybrid cross A monohybrid cross involves determining trait inheritance by orking ith only one trait at a time. 208 Student Pages

29 Dihybrid cross A dihybrid cross involves determining trait inheritance by orking ith to traits at a time. Mendelian trait Mendelian traits have to alleles for a single trait. Only one gene determines the trait, and the gene has to alleles. One allele is dominant, and the other is recessive. The environment does not affect either of the alleles. Non-Mendelian trait A non-mendelian trait is controlled by more than one gene and has many alleles. There is no true dominance or recessiveness among the many alleles. For example, hair color in humans is controlled by more than one gene and many alleles. Some alleles may be affected by environmental conditions. For example, the fur of arctic rabbits turns hite in cold temperatures and bron in arm temperatures. X-linked trait or sex-linked trait An X-linked trait is found only on the X chromosome. Hemophilia, a blood abnormality in humans, is an example of a trait found only on the X chromosome. Student Pages 209

30 STAAR Biology: Assessment Activities 210 Student Pages