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Warm Up: For these Guinea pigs, tan hair is dominant over black. • 1. What are the genotypes for each individual? • 2. Who is homozygous and who is heterozygous? • ----------------------------- • • • • Dad Mom tt Tt tt What are the alleles? What are the genotypes/phenotypes? Baby Where did the ALL alleles come from? Predict the likelihood that this genotype/ phenotype would result. Key Ideas • How can a Punnett square be used in genetics? • How can mathematical probability be used in genetics? Objectives: Using Mendelian Genetics • Describe how a Punnett square is used in genetics. • List ways to express mathematical probability in genetics. Vocabulary • Punnett square • Probability • Pedigree • Genetic disorder What You Should Recall. We’re looking at this… • You know that Mendel gave us two important laws. • Independent assortment: Speaks to the fact that genes separate independent of one another • Segregation: Speaks to the fact that alleles of the same gene have equal probability of segregating into gametes. • Once the gametes are formed, “Mendelian genetics” also gives us an outline on how to figure out what the likelihood, the probability, of an offspring has to show particular traits, based upon dominant & recessive alleles. • Today you will learn how to figure out the probability of certain traits being inherited and shown, using Punnett Squares. Using Punnett Squares • How can you predict the chances an offspring will have a certain genotype, therefore phenotype? • A Punnett square is a model that predicts the probability of likely outcomes of a genetic cross. • Remember that a cross is “to mate or breed two individuals.” • A Punnett square shows all of the genotypes that could result from a given hybrid cross. • The important thing to remember is that this shows what could happen…not necessarily what always happens. • The simplest Punnett square consists of a square divided into four boxes. • This is a monohybrid cross… • The combination of letters in each box represents one possible genotype in the offspring. Meiosis EVERY CHILD BORN WOULD HAVE THE SAME CHANCES TO INHERIT ANY OF THE COMBINATIONS OF ALLELES! Fertilization Meiosis Probable zygotes that can be produced by one fertilization Using Punnett Squares Constructing a Simple Punnett square for Monohybrid Crosses 1. 2. 3. Draw a 2 x 2 chart. Conclude what the genotype of the parents’ gametes are based upon the description given. Write the GENOTYPE of the parents’ gametes on the top and sides of the chart. There is one letter per column & row. This represents the allele being donated by a gamete during fertilization. 4. Fill in the columns and rows corresponding with the heading allele. Y y y Y Yy Yy These are the possible allele combinations for Yythe offspring Yy Ratios and Punnett Squares • A Punnett square basically predicts: .. • all the possible combinations for alleles for each trait examined. • This can be use to predict the likelihood of traits of an offspring… the probability of things happening. • It also reveals the ratio of one type of offspring compared to the other types offspring. • The ratio can help compare genotypes to other genotypes or phenotypes to other phenotypes. • It ultimately shows how the possible offspring compare to the other offspring. Ratio Review • What is a ratio? • A ratio is an expression, of at least two numbers, that is used to compare values. • It is written separated by a colon. • Ex. If there are (normally) 5 fingers for every hand would be written as 5:1 ratio of fingers to hands. • It would be said as “a ratio of 5 fingers to one hand” • A ratio shows how many events happen compared to the events of others. Ratios of Fingers to Hands • There is a ratio of five fingers to every one hand. • Written: 5:1 1 2 3 4 5 1 Using Punnett Squares • Punnett squares give us genotypes probabilities to determine phenotypes. • In a monohybrid homozygous dominant cross, all of the offspring will be homozygous. • The ratio of the genotypes will be 1 YY:0 [others], meaning all the offspring will be the same genotype for the alleles. • This is called the genotypic ratio. • The phenotypic ratio describes the comparison of all the traits displayed. • The phenotypic ratio here is all the dominant form… all dominant. Y Y YY Y YY Y YY YY Using Punnett Squares • In a monohybrid cross between a homozygous dominant and a homozygous recessive all the offspring will be heterozygous (ex. Yy). • What are the genotypic & phenotypic ratios here? • The genotypic ratio would again be • 1Yy:0 [others]. • Because there is no other alternative, there is no other thing to compare to. • Since there’s only 1 genotype, there can be only 1 phenotype. • As such, the phenotypes would be all the dominant form. Y y Yy Y Yy y Yy Yy Using Punnett Squares • In a monohybrid heterozygous cross the genotypic ratio will be 1 YY : 2 Yy : 1 yy. • This is what Mendel observed in his F2 generations! • What is the phenotypic ratio? Y Y YY y Yy y Yy yy • 3 yellow (dominant): 1 green (recessive) Using Punnett Squares • Phenotypes • Remember, genotype determines phenotype, but the ratio is not always the same between the two. • You need to think about the trait that will be shown depending upon the allele combination. • In a monohybrid cross between homozygotes all the offspring will be the same, therefore all the offspring will express the same trait. • However, in a monohybrid heterozygote cross, where the genotypic ratio is 1 : 2 : 1, • the phenotypic ratio will be 3 : 1. Punnett Squares Dihybrid Crosses Mendel noticed that alleles for one gene do not affect the inheritance of the alleles for another gene. = independent assortment • This makes predicting the probability of inheriting a combination of two non-linked genes more challenging but entirely possible. • What does nonlinked mean? Dihybrid Crosses. • In order to accomplish this you must consider all possible gametes for an individual, then perform the cross. • Let’s try crossing two heterozygotes for pea color and flower color. • PpYy x PpYy • Take a minute and figure out the possible gametes. Dihybrid Crosses. • In order to accomplish this you must consider all possible gametes for an individual, then perform the cross. • Let’s try crossing two heterozygotes for pea color and flower color. • PpYy x PpYy • Take a minute and figure out the possible gametes. PY Dihybrid Crosses. • In order to accomplish this you must consider all possible gametes for an individual, then perform the cross. • Let’s try crossing two heterozygotes for pea color and flower color. • PpYy x PpYy • Take a minute and figure out the possible gametes. PY pY Dihybrid Crosses. • In order to accomplish this you must consider all possible gametes for an individual, then perform the cross. • Let’s try crossing two heterozygotes for pea color and flower color. • PpYy x PpYy • Take a minute and figure out the possible gametes. PY pY Py Dihybrid Crosses. • In order to accomplish this you must consider all possible gametes for an individual, then perform the cross. • Let’s try crossing two heterozygotes for pea color and flower color. • PpYy x PpYy • Take a minute and figure out the possible gametes. PY pY Py py Dihybrid Crosses. • In order to accomplish this you must consider all possible gametes for an individual, then perform the cross. • Let’s try crossing two heterozygotes for pea color and flower color. • PpYy x PpYy… Conduct the cross, calculate probabilities. PY PY pY Py py pY Py py CW/HW • Complete both sides of the worksheet by next class (25pts). We will develop this and work on trihybrid crosses tomorrow. • Questions on HW. • Answers, then trihybrid. Trihybrid Crosses • We have over 30,000 genes. • Not all of them are “Mendelian” but many are. • How would you predict the chances an individual inherited this combination of Mendelian traits from two heterozygotes: • • • • • • Cleft chin (d) No dimples (r) A widows peak (d) Attached ear lobes (r) Hitchhikers thumbs (r) & freckles? (d) .75 .75x.25 .75x.25x.75 .75x.25x.75x.25 .75x.25x.75x.25x.25 .75x.25x.75x.25x.25x.75 = 0.66% (7 out of 1000) • The more variables you consider the higher the degree of difficulty is inherent. • We’ll stop at three different, non-linked genes but considering these will help you appreciate just how unique you are! • The probabilities of another person inheriting the exact same combination of alleles you did is nearly impossible. Trihybrid Crosses • Consider crossing heterozygotes for flower color, pea color, & pea shape. • PpYyRr x PpYyRr • What should you do? • First identify all the gametes that could form from each parent (independent assortment & segregation assumed). • PYR – PYr – PyR – Pyr – pYR – pYr – pyR – pyr • Then set up your 8 x 8 grid and distribute the gametes. 2nd: Distribute gametes PYR – PYr – PyR – Pyr – pYR – pYr – pyR – pyr PYR PYr PYR PYr PyR Pyr pYR pYr pyR pyr PyR Pyr pYR pYr pyR pyr Combine gametes and analyze. What is the: - Genotypic ratio? Phenotypic ratio? PYR PYr PyR Pyr pYR pYr pyR pyr PYR PPYYRR PPYYRr PPYyRR PPYyRr PpYYRR PpYYRr PpYyRR PpYyRr PYr PPYYRr PPYYrr PPYyRr PPYyrr PpYYRr PpYYrr PpYyRr PpYyrr PyR PPYyRR PPYyRr PPyyRR PPyyRr PpYyRR PpYyRr PpyyRR PpyyRr Pyr PPYyRr PPYyrr PPyyRr PPyyrr PpYyRr PpYyrr PpyyRr Ppyyrr pYR PpYYRR PpYYRr PpYyRR PpYyRr ppYYRR ppYYRr ppYyRR ppYyRr pYr PpYYRr PpYYrr PpYyRr PpYyrr ppYYRr ppYYrr ppYyRr ppYyrr pyR PpYyRR PpYyRr PpyyRR PpyyRr ppYyRR ppYyRr ppyyRR ppyyRr pyr PpYyRr PpYyrr PpyyRr Ppyyrr ppYyRr ppYyrr ppyyRr ppyyrr What is the: - Genotypic ratio? Phenotypic ratio? GR=1PPYYRR:2PPYYRr:2PPYyRR:1PPYYrr:4PPYyRr:2PPYyrr:1PPyyRR:2PPyyRr:1PPyyrr: 2PpYYRR:4PpYYRr:2PpYYrr:4PpYyRR:8PpYyRr:4PpYyrr:2PpyyRR:4PpyyRr:2Ppyyrr:1ppYYRR: 2ppYYRr: 1ppYYrr:2ppYyRR:4ppYyRr:2ppYyrr:1ppyyRR:2ppyyRr:1ppyyrr PR=27PYR:9PYw:9PgR:3Pgw:9wYR:3wgR:3wYw:1wgw PYR PYr PyR Pyr pYR pYr pyR pyr PYR PPYYRR PPYYRr PPYyRR PPYyRr PpYYRR PpYYRr PpYyRR PpYyRr PYr PPYYRr PPYYrr PPYyRr PPYyrr PpYYRr PpYYrr PpYyRr PpYyrr PyR PPYyRR PPYyRr PPyyRR PPyyRr PpYyRR PpYyRr PpyyRR PpyyRr Pyr PPYyRr PPYyrr PPyyRr PPyyrr PpYyRr PpYyrr PpyyRr Ppyyrr pYR PpYYRR PpYYRr PpYyRR PpYyRr ppYYRR ppYYRr ppYyRR ppYyRr pYr PpYYRr PpYYrr PpYyRr PpYyrr ppYYRr ppYYrr ppYyRr ppYyrr pyR PpYyRR PpYyRr PpyyRR PpyyRr ppYyRR ppYyRr ppyyRR ppyyRr pyr PpYyRr PpYyrr PpyyRr Ppyyrr ppYyRr ppYyrr ppyyRr ppyyrr How many (out of 64) will be: - Purple flowers, Yellow peas, Round peas? What is the: - Genotypic ratio? - Phenotypic ratio? 1PPYYRR:2PPYYRr:2PPYyRR:1PPYYrr:4PPYyRr:2PPYyrr:1PPyyRR: 2PPyyRr:1PPyyrr:2PpYYRR:4PpYYRr:2PpYYrr:4PpYyRR:8PpYyRr: 4PpYyrr:2PpyyRR:4PpyyRr:2Ppyyrr:1ppYYRR:2ppYYRr: 1ppYYrr:2ppYyRR:4ppYyRr:2ppYyrr:1ppyyRR:2ppyyRr:1ppyyrr 27PYR:9PYw:9PgR:3Pgw:9wYR:3wgR:3wYw:1wgw - white flowers, green peas, wrinkled peas? Purple flowers, green peas, Round peas? white flowers, Yellow peas, Round peas? Purple flowers, green peas, wrinkled peas? Heterozygous for all three traits? 27 of 64 PYR PYr PyR Pyr pYR pYr pyR pyr PYR PPYYRR PPYYRr PPYyRR PPYyRr PpYYRR PpYYRr PpYyRR PpYyRr PYr PPYYRr PPYYrr PPYyRr PPYyrr PpYYRr PpYYrr PpYyRr PpYyrr PyR PPYyRR PPYyRr PPyyRR PPyyRr PpYyRR PpYyRr PpyyRR PpyyRr Pyr PPYyRr PPYyrr PPyyRr PPyyrr PpYyRr PpYyrr PpyyRr Ppyyrr pYR PpYYRR PpYYRr PpYyRR PpYyRr ppYYRR ppYYRr ppYyRR ppYyRr pYr PpYYRr PpYYrr PpYyRr PpYyrr ppYYRr ppYYrr ppYyRr ppYyrr pyR PpYyRR PpYyRr PpyyRR PpyyRr ppYyRR ppYyRr ppyyRR ppyyRr pyr PpYyRr PpYyrr PpyyRr Ppyyrr ppYyRr ppYyrr ppyyRr ppyyrr How many (out of 64) will be: What is the: - Genotypic ratio? - Phenotypic ratio? 1PPYYRR:2PPYYRr:2PPYyRR:1PPYYrr:4PPYyRr:2PPYyrr:1PPyyRR: 2PPyyRr:1PPyyrr:2PpYYRR:4PpYYRr:2PpYYrr:4PpYyRR:8PpYyRr: 4PpYyrr:2PpyyRR:4PpyyRr:2Ppyyrr:1ppYYRR:2ppYYRr: 1ppYYrr:2ppYyRR:4ppYyRr:2ppYyrr:1ppyyRR:2ppyyRr:1ppyyrr 27PYR:9PYw:9PgR:3Pgw:9wYR:3wgR:3wYw:1wgw - Purple flowers, Yellow peas, Round peas? - white flowers, green peas, wrinkled peas? - Purple flowers, green peas, Round peas? white flowers, Yellow peas, Round peas? Purple flowers, green peas, wrinkled peas? Heterozygous for all three traits? 1 of 64 PYR PYr PyR Pyr pYR pYr pyR pyr PYR PPYYRR PPYYRr PPYyRR PPYyRr PpYYRR PpYYRr PpYyRR PpYyRr PYr PPYYRr PPYYrr PPYyRr PPYyrr PpYYRr PpYYrr PpYyRr PpYyrr PyR PPYyRR PPYyRr PPyyRR PPyyRr PpYyRR PpYyRr PpyyRR PpyyRr Pyr PPYyRr PPYyrr PPyyRr PPyyrr PpYyRr PpYyrr PpyyRr Ppyyrr pYR PpYYRR PpYYRr PpYyRR PpYyRr ppYYRR ppYYRr ppYyRR ppYyRr pYr PpYYRr PpYYrr PpYyRr PpYyrr ppYYRr ppYYrr ppYyRr ppYyrr pyR PpYyRR PpYyRr PpyyRR PpyyRr ppYyRR ppYyRr ppyyRR ppyyRr pyr PpYyRr PpYyrr PpyyRr Ppyyrr ppYyRr ppYyrr ppyyRr ppyyrr How many (out of 64) will be: What is the: - Genotypic ratio? - Phenotypic ratio? 1PPYYRR:2PPYYRr:2PPYyRR:1PPYYrr:4PPYyRr:2PPYyrr:1PPyyRR: 2PPyyRr:1PPyyrr:2PpYYRR:4PpYYRr:2PpYYrr:4PpYyRR:8PpYyRr: 4PpYyrr:2PpyyRR:4PpyyRr:2Ppyyrr:1ppYYRR:2ppYYRr: 1ppYYrr:2ppYyRR:4ppYyRr:2ppYyrr:1ppyyRR:2ppyyRr:1ppyyrr 27PYR:9PYw:9PgR:3Pgw:9wYR:3wgR:3wYw:1wgw - Purple flowers, Yellow peas, Round peas? white flowers, green peas, wrinkled peas? - Purple flowers, green peas, Round peas? - white flowers, Yellow peas, Round peas? Purple flowers, green peas, wrinkled peas? Heterozygous for all three traits? 9 of 64 PYR PYr PyR Pyr pYR pYr pyR pyr PYR PPYYRR PPYYRr PPYyRR PPYyRr PpYYRR PpYYRr PpYyRR PpYyRr PYr PPYYRr PPYYrr PPYyRr PPYyrr PpYYRr PpYYrr PpYyRr PpYyrr PyR PPYyRR PPYyRr PPyyRR PPyyRr PpYyRR PpYyRr PpyyRR PpyyRr Pyr PPYyRr PPYyrr PPyyRr PPyyrr PpYyRr PpYyrr PpyyRr Ppyyrr pYR PpYYRR PpYYRr PpYyRR PpYyRr ppYYRR ppYYRr ppYyRR ppYyRr pYr PpYYRr PpYYrr PpYyRr PpYyrr ppYYRr ppYYrr ppYyRr ppYyrr pyR PpYyRR PpYyRr PpyyRR PpyyRr ppYyRR ppYyRr ppyyRR ppyyRr pyr PpYyRr PpYyrr PpyyRr Ppyyrr ppYyRr ppYyrr ppyyRr ppyyrr How many (out of 64) will be: What is the: - Genotypic ratio? - Phenotypic ratio? 1PPYYRR:2PPYYRr:2PPYyRR:1PPYYrr:4PPYyRr:2PPYyrr:1PPyyRR: 2PPyyRr:1PPyyrr:2PpYYRR:4PpYYRr:2PpYYrr:4PpYyRR:8PpYyRr: 4PpYyrr:2PpyyRR:4PpyyRr:2Ppyyrr:1ppYYRR:2ppYYRr: 1ppYYrr:2ppYyRR:4ppYyRr:2ppYyrr:1ppyyRR:2ppyyRr:1ppyyrr 27PYR:9PYw:9PgR:3Pgw:9wYR:3wgR:3wYw:1wgw - Purple flowers, Yellow peas, Round peas? white flowers, green peas, wrinkled peas? Purple flowers, green peas, Round peas? - white flowers, Yellow peas, Round peas? - Purple flowers, green peas, wrinkled peas? Heterozygous for all three traits? 9 of 64 PYR PYr PyR Pyr pYR pYr pyR pyr PYR PPYYRR PPYYRr PPYyRR PPYyRr PpYYRR PpYYRr PpYyRR PpYyRr PYr PPYYRr PPYYrr PPYyRr PPYyrr PpYYRr PpYYrr PpYyRr PpYyrr PyR PPYyRR PPYyRr PPyyRR PPyyRr PpYyRR PpYyRr PpyyRR PpyyRr Pyr PPYyRr PPYyrr PPyyRr PPyyrr PpYyRr PpYyrr PpyyRr Ppyyrr pYR PpYYRR PpYYRr PpYyRR PpYyRr ppYYRR ppYYRr ppYyRR ppYyRr pYr PpYYRr PpYYrr PpYyRr PpYyrr ppYYRr ppYYrr ppYyRr ppYyrr pyR PpYyRR PpYyRr PpyyRR PpyyRr ppYyRR ppYyRr ppyyRR ppyyRr pyr PpYyRr PpYyrr PpyyRr Ppyyrr ppYyRr ppYyrr ppyyRr ppyyrr What is the: - Genotypic ratio? - Phenotypic ratio? How many (out of 64) will be: - Purple flowers, Yellow peas, Round peas? white flowers, green peas, wrinkled peas? Purple flowers, green peas, Round peas? white flowers, Yellow peas, Round peas? 1PPYYRR:2PPYYRr:2PPYyRR:1PPYYrr:4PPYyRr:2PPYyrr:1PPyyRR: 2PPyyRr:1PPyyrr:2PpYYRR:4PpYYRr:2PpYYrr:4PpYyRR:8PpYyRr: 4PpYyrr:2PpyyRR:4PpyyRr:2Ppyyrr:1ppYYRR:2ppYYRr: 1ppYYrr:2ppYyRR:4ppYyRr:2ppYyrr:1ppyyRR:2ppyyRr:1ppyyrr 27PYR:9PYw:9PgR:3Pgw:9wYR:3wgR:3wYw:1wgw - Purple flowers, green peas, wrinkled peas? - Heterozygous for all three traits? 3 of 64 PYR PYr PyR Pyr pYR pYr pyR pyr PYR PPYYRR PPYYRr PPYyRR PPYyRr PpYYRR PpYYRr PpYyRR PpYyRr PYr PPYYRr PPYYrr PPYyRr PPYyrr PpYYRr PpYYrr PpYyRr PpYyrr PyR PPYyRR PPYyRr PPyyRR PPyyRr PpYyRR PpYyRr PpyyRR PpyyRr Pyr PPYyRr PPYyrr PPyyRr PPyyrr PpYyRr PpYyrr PpyyRr Ppyyrr pYR PpYYRR PpYYRr PpYyRR PpYyRr ppYYRR ppYYRr ppYyRR ppYyRr pYr PpYYRr PpYYrr PpYyRr PpYyrr ppYYRr ppYYrr ppYyRr ppYyrr pyR PpYyRR PpYyRr PpyyRR PpyyRr ppYyRR ppYyRr ppyyRR ppyyRr pyr PpYyRr PpYyrr PpyyRr Ppyyrr ppYyRr ppYyrr ppyyRr ppyyrr How many (out of 64) will be: What is the: - Genotypic ratio? - Phenotypic ratio? 1PPYYRR:2PPYYRr:2PPYyRR:1PPYYrr:4PPYyRr:2PPYyrr:1PPyyRR: 2PPyyRr:1PPyyrr:2PpYYRR:4PpYYRr:2PpYYrr:4PpYyRR:8PpYyRr: 4PpYyrr:2PpyyRR:4PpyyRr:2Ppyyrr:1ppYYRR:2ppYYRr: 1ppYYrr:2ppYyRR:4ppYyRr:2ppYyrr:1ppyyRR:2ppyyRr:1ppyyrr 27PYR:9PYw:9PgR:3Pgw:9wYR:3wgR:3wYw:1wgw - Purple flowers, Yellow peas, Round peas? white flowers, green peas, wrinkled peas? Purple flowers, green peas, Round peas? white flowers, Yellow peas, Round peas? Purple flowers, green peas, wrinkled peas? - Heterozygous for all three traits? 8 of 64 PYR PYr PyR Pyr pYR pYr pyR pyr PYR PPYYRR PPYYRr PPYyRR PPYyRr PpYYRR PpYYRr PpYyRR PpYyRr PYr PPYYRr PPYYrr PPYyRr PPYyrr PpYYRr PpYYrr PpYyRr PpYyrr PyR PPYyRR PPYyRr PPyyRR PPyyRr PpYyRR PpYyRr PpyyRR PpyyRr Pyr PPYyRr PPYyrr PPyyRr PPyyrr PpYyRr PpYyrr PpyyRr Ppyyrr pYR PpYYRR PpYYRr PpYyRR PpYyRr ppYYRR ppYYRr ppYyRR ppYyRr pYr PpYYRr PpYYrr PpYyRr PpYyrr ppYYRr ppYYrr ppYyRr ppYyrr pyR PpYyRR PpYyRr PpyyRR PpyyRr ppYyRR ppYyRr ppyyRR ppyyRr pyr PpYyRr PpYyrr PpyyRr Ppyyrr ppYyRr ppYyrr ppyyRr ppyyrr Punnett Square Practice/Homework Complete the worksheet. Check the website for the answers. - Ask questions if you don’t understand. - Pay attention to the process so you can get it right. Wednesday February 6, 2013 Copy onto your ‘Quizzie’ paper the following question. Answer it and save it to turn in. If you don’t know an answer, get a book and find it or review with a friend. Blanks will count against you and wrong answers don’t help you. • Quizzie • Q1: If a mom that’s homozygous recessive for hair color (she’s blonde) and a dad is heterozygous for hair color (he has black hair), what will be the possible genotypes of any children they have? Show this with a Punnett Square. • Q2: What chance do the children have to get blonde hair? • Q3: What are the ratios for the genotypes and phenotypes? 50% chance • ----------------------------of getting blonde hair b b • Agenda: • Check Punnett Squares • Discussion: Test Crosses. • QL: Test Crosses B Bb Bb GR: 1:1 b bb bb PR: 1:1 Punnett Squares: Answers P PP PP #3 100%PP Phenotypic Ratio: 1Purple:0(all);100%Purple GR: 1Yy:0 PR: 1Yellow:0 100% Yy 100%yellow #2 #4 P P PP p Pp p Pp pp #1 P P PP P PP Genotypic Ratio: 1PP:0 (all) G g Gg g gg g Gg gg GR: 1Gg:1gg 50%Gg, 50%gg PR: 1green: 1yellow; 50%green, 50%yellow Y Y y Yy Yy y Yy Yy GR: 1PP:2Pp:1pp; 25%PP, 50% Pp, 25%pp PR: 3purple: 1white; 75%purple, 25%white Thursday February 7, 2013 Copy onto your ‘Quizzie’ paper the following question. Answer it and save it to turn in. If you don’t know an answer, get a book and find it or review with a friend. Blanks will count against you and wrong answers don’t help you. • Quizzie #3: Imagine you are a farmer and wanted to start selling green sweet peas (what Mendel produced and studied). You buy a pea plant that is sold to you as a true-breeding green pea plant for nice round peas. You are skeptical because the guy who sold it to you seemed shady. You are intending to plant several acres with this plant’s seeds and have a lucrative business. • Q1: What specific technique could you perform to find out exactly what the genotype of your plant is? • Q2: What phenotype would you want all the offspring from this technique to be? • Q3: If the offspring of a test cross all have the dominant trait, is the genotype of the individual being tested heterozygous or homozygous? -------------------• Agenda: • Discussion: Probabilities • Penny Genetics Lab • Hand in Testcross MiniLab Using Probability • A Punnett square shows the possible outcomes of a cross, but it also is used to calculate the probability of each outcome. • Probability is the likelihood that a specific event will occur out of the total number of events. • Probability can be calculated and expressed in many ways. • Probability can be expressed in words, as a decimal, as a percentage, or as a fraction. Using Probability, continued • Probability formulas can be used to predict the probabilities that specific alleles will be passed on to offspring. • Probabilities are usually expressed as decimals or as percentages although fractions are okay. • 2/4 = ½ • ¼ • ¾ = 0.5 = 0.25 = 0.75 = 50% = 25% = 75% • The possible results of a heterozygous cross (which is trying to predict the genotypes of offspring from the mating of two heterozygotes) are similar to those of flipping two coins at once. • This is where we will begin our testing. Using Probability • Punnet Squares are nice tools to use but the real question remains… • How can you be sure that the Punnet squares accurately show how genetics really works? • The solution will hopefully be revealed in the next exercise… • Penny Genetics Penny Genetics Lab Testing the validity of Punnett Squares. • Get into groups of two (max). Get one packet per pair. • In groups of two you will perform an investigation into whether Punnett Squares can be used to predict randomness of nature. • For the next 5 minutes… Completely read the lab intro & skim the rest. I’ll answer questions then. • A Punnett Square makes a prediction but does it match the randomness in nature? Perform a Punnett Square and then flip coins to see if they match. • Part I: First: Figure out the PHENOTYPES based upon the description. Second: Predict if the PUNNETT SQUARE will match the COIN FLIPS Third: Complete the PUNNETT SQUARE (this is the prediction) Fourth: Flip the COINS 100x. Fifth: COMPARE the two. • You may write on the lab, but don’t lose it or you’ll have to hand write it or print it off the website. • Your objective is to get through all of Part I & Part II if everything goes good so work diligently! Complete everything today to save yourself homework. • This Lab is worth 125 points. Due Friday. Monday February 11, 2013 Copy onto your ‘Quizzie’ paper the following question. Answer it and save it to turn in. If you don’t know an answer, get a book and find it or review with a friend. Blanks will count against you and wrong answers don’t help you. • Quizzie #4: In pea plants, tallness (T) is dominant to shortness (t). Crosses between plants with these traits can be analyzed using a Punnett square similar to the one shown below. T t T 1 2 t 3 4 • Q1: Complete this Punnett Square. • Q2: Box 2 and box ____________________ in the Punnett square represent plants that would be heterozygous for the trait for tallness. • Q3: The phenotype of the plant that would be represented in box 4 of the Punnett square would be ____________________. -------------------------------------------------------------------------------------------------------------------------------- • Agenda: • Discussion: Pedigrees • In-class/ HW Activity Pedigree Analysis • Penny Genetics DUE. Turn these in to the inbox. Applications of Mendelian Genetics • Families can sometimes be surprised when recessive traits “pop up” out of seemingly nowhere. • Not knowing how genetics works can stress people out unnecessarily. • If a child expresses, shows, a recessive trait but the parents express the dominant trait what are the genotypes of the parents & how can you figure this out? The point of using a Punnett Square • Punnett squares are useful when predicting the ratios of offspring. • For example, is you want to know the probability of how many siblings in your family can have the phenotype of black hair your can calculate that if you know the genotypes of your parents. • But what if you don’t know their genotypes? • The 1st option is using a test cross. Test Cross Mini Lab • If you aren’t sure what the genotype of a parent showing a dominant trait is you perform a test cross. • In a test cross, you always cross the unknown with a homozygous recessive individual. • The difference is in the “?” allele. • What does it mean if half of the offspring show the recessive trait? B ? b Bb b? b Bb b? Test Cross • The test-cross mating can have two possible phenotype outcomes. • All dominant offspring • What would the “?” have to be? B ? b Bb b? b Bb b? Test Cross • The test-cross mating can have two possible phenotype outcomes. • Half recessive offspring. • What would the “?” have to be? B ? b Bb b? b Bb b? Genes Linked Within Chromosomes • Many traits do not follow Mendel’s laws because he studied the simplest kinds of heredity where characters are determined by independent genes. • Genes that are close together, as well as the traits they determine, are said to be linked. • During meiosis, genes that are linked (close together) on the same chromosome are less likely to be separated than genes that are far apart. • We discussed this in Punnett Squares when we challenged independent assortment. • Linked genes tend to be inherited together. • Sex-linked genes are those genes inherited together based upon gender chromosomes. Not-Linked Not-Linked Linked Linked Linked v Non-linked What is Sex-Linked? How does it happen? X Y STANDARD GENDER DISTRIBUTION PROBABILITY = 50% MALE - 50% FEMALE X XX XY X XX XY X Y STANDARDCGENDER DISTRIBUTION PROBABILITY = 50/50 BUT ADD INTO THE MIX COLOR-BLINDNESS, C XCXC XCY WHICH IS ONLY FOUND ON THE ‘X’ CHROMOSOME c XCXc XcY X X A Sex-Linked Trait Red-Green Color Blindness Can you see the numbers? Trace from x to x… there’s a line there. X X Sex-Linked Gene Inheritance Notice the distribution of the alleles. In this case you must take two things into account. Sex & the allele. XC Xc XC XC XCXC Y XC XcY Test Crosses & Linkage Exercises • Complete the worksheet for homework. Show the cross of a man who has hemophilia with a woman who is a carrier along with the genotypic/phenotypic ratios for the possible offspring. GR: 1XHXh:1XhXh:1XHY:1XhY PR: 2 F Norm: 1 M Norm: 1 M Hemophilia XH Xh Xh XHXh XhXh Y XHY XhY The Royal Disease • European Royalty in the 19th & 20th centuries came with a price. • Although many were spared the horrible tragedy of bleeding to death, some were not so lucky due to the pervasive recessive X-linked trait hemophilia. Hemophilia in History: Study in pedigree. The most famous example. Men who died of Hemophilia in Order of Death Name Death Relation to Queen Victoria Prince Friedrich of Hesse and by Rhine 29-May-1873 grandson The Prince Leopold, Duke of Albany 28-Mar-1884 son Prince Heinrich Friedrich of Prussia 26-Feb-1904 great grandson Lord Leopold Mountbatten 23-Apr-1922 grandson Prince Rupert of Teck 15-Apr-1928 great grandson Infante Gonzalo of Spain 13-Aug-1934 great grandson Alfonso, Prince of Asturias 6-Sep-1938 great grandson Prince Waldemar of Prussia 2-May-1945 great grandson Pedigrees. Genetics Tool • Now: • Karyotyping: Detect obvious chromosome abnormalities • Genetic testing: Detect hidden mutations in DNA • Some disabilities aren’t fatal • Red-green color blindness • Albinism • But others are: • Hemophilia • Duchene muscular dystrophy • Do you think it’s important to study these diseases and how they are passed through families? Pedigrees • Other than determining the probabilities of Mendelian traits being inherited and displayed in a monohybrid cross (aka Punnett Square), geneticists use another tool, called a pedigree, to identify patterns of inheritance in multiple generations. http://www.youtube.com/watch?v= W7x1ETPkZsk Using a Pedigree • • • Mendel observed several generations of pea plants to help identify some trends in heredity. His observation of inheritance is a good example of performing an isolated family history study to see how a trait is inherited. A pedigree is a similar study, except over many generations. • A pedigree is a diagram that shows several generations of a family and the occurrence of certain genetic characteristics. • A primary reason a pedigree is used is to help a family understand a genetic disorder and how it’s passed on. • A genetic disorder is a disease or disorder that can be inherited. Using a Pedigree • A pedigree can help answer questions about three aspects of inheritance: 1.Sex linkage - To identify which deleterious genes are located on the X chromosome (deleterious = BAD) 2.Dominance - Identify the dominant or recessive alleles 3.Heterozygosity (aka a Carriers for a disease) - Help determine the genotype of parents. Hemophilia High blood pressure DMD Congenital night blindness • The sex chromosomes, X and Y, carry genes for many characters other than gender. Using a Pedigree: Sex Linked Genes • A sex-linked gene is located on either an X or a Y chromosome. • Traits that are not expressed equally in both sexes are commonly sex-linked traits. • Examples: • Colorblindness: a sex-linked trait that is expressed more in males than in females. • Baldness: expressed more in males • Any other ones?... Using a Pedigree: Dominance, Carriers • Dominance: If a person has a trait that is autosomal (meaning what?) and dominant and has even one dominant allele, he or she will show the trait. • Dominant traits have a tendency to show up more often than not. • They do follow Mendelian probabilities though. • Heterozygosity: If a person is either heterozygous or homozygous dominant for an autosomal gene, his or her phenotype will show the dominant trait. • If a person heterozygous for a recessive trait he or she will not show the trait but can and may pass it on. • Why would the trait not be passed on? • There is a 50/50 chance of passing it on. • Persons carrying the recessive allele but not displaying the trait are called carriers. Pedigree Basic Symbols Horizontal lines show relationships that produced offspring The character key: Vertical lines show offspring from the pair A female A male A female with trait A male with trait Carrier (ex. Male) Group Questions. Using alleles A, a, you have 5 minutes to discuss with your group and answer. 1. What is the sex of individual #3? 2. Who shows the trait? 3. Is this trait dominant or recessive? Why? 4. What is the genotype of individual #3? 5. What are the genotypes of Mom & Dad? 6. Who can you not determine the genotype for? 7. BONUS: Is this trait sex-linked? How do you know? 1. Female 2. Female #3 3. Recessive or mom & dad would have it. 4. aa 5. Aa, Aa 6. Siblings 1, 2, & 4 7. No, otherwise dad would have the trait too. One of the X’s for #3 would have to come from dad. Using a Pedigree: Strategy Remember… • If a person is homozygous recessive, his or her phenotype will show the recessive trait. • A recessive trait in a child shows that both parents were heterozygous carriers of that recessive allele. • Dominant traits show up more often than recessive. • Look for the people displaying the trait! Using logic you can determine the parent’s genotypes then the siblings. 1. Pedigree Analysis Practice. (CW/HW: 25pts) 1. Example 1 has 2 unknowns, not 9. 2. Pedigree Mini-Lab exercise. (HW) You may work in groups of two and you can write on the worksheet. Problems should be worked out today and this is due tomorrow. It is worth 25 pts (1/4 lab). Summary • A Punnett square shows all of the genotypes that could result from a given cross. • Probability formulas can be used to predict the probabilities that specific alleles will be passed on to offspring. • A pedigree can help answer questions about three aspects of inheritance: sex linkage, dominance, and heterozygosity. Genotypes Allele combo FF Ff Phenotypes Trait Ff f f Aa Aa aa Aa ?? aa ?? Aa ?? ?? Aa ?? Aa Aa aa ?? aa ?? ?? Aa aa Aa Aa ?? aa ?? Aa Section 12.1-12.3 Quiz • • • • • • • • • The quiz says “12. & 12.2” but it’s for sections 12.1-12.3. Write all answers on a separate sheet of paper. Do not write on the quiz. If you write on the quiz you will get a zero. You may use books. Correct answers are worth 1 pt. ea. You do not need to write complete sentences. Double check your work before you turn them in. Turn in your answers to the test/quiz tray in the back. ________ ________ ________ ________ ________ ________ ________ 2 otype _____ ______ ______ ______ ______ ______ ______
