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Genetics: Testing Hypotheses about Inheritance

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Genetics: Testing Hypotheses about Inheritance;Introduction;Fruit Fly Background and Life Cycle;In this exercise, you will perform reciprocal crosses to determine the inheritance pattern of various traits in Drosophila;melanogaster. This organism has been used in genetic experiments since 1910. Wild type or normal traits are red;eyes, wings longer than the body and smooth, and tan or brown body color. An enormous number of mutants;spontaneous and induced, have been discovered in Drosophila, including mutations that affect external anatomy (eye;color, body size, body color, and wing shape). The most interesting mutations are those that affect behavior. Mutants;have been found that go into shock at loud noises, forget recently learned things and show excessive libido.;Drosophila are useful for laboratory experiments, because they have a short generation time, produce many offspring;and require no special care or equipment. The life cycle of Drosophila (see Figure 1) is usually completed in 14 days if;incubated at 21C, or in 10 days at 24C. The life cycle includes four stages: egg, larva, pupa and adult. The eggs are 2;mm long, sausage-shaped, and white, bearing a pair of filaments at one end, which keep the eggs from sinking into the;soft food on which they are always laid. One day after being laid, the eggs hatch into first instar larvae (little white;maggots), which feed voraciously. After several days, the larvae molt and begin the second instar developing tracheae.;One more molt occurs to produce third instar larvae, which crawl onto a hard dry surface and transform into pupae in;small dark cocoons. Within the pupae, the third instar larvae go through metamorphosis and eventually emerge as;adult flies. A few hours after emergence, the adult is at first light in color with crumpled wings. Within a few hours, the;flies wings expand and harden, enabling them to fly.;Figure 1. Diagram of Drosophila life cycle.;How we talk about genetic information;Each cell in living organisms contains DNA, which is made of nucleotide subunits arranged in very long strands. By;winding around structural proteins, the strands become condensed into compact units called chromosomes. Regions;in the DNA, known as genes, carry specific instructions for making proteins. Genes represent unique combinations of;nucleotides that provide information for the genetically-based traits that organisms display.;While all humans have the same genes (that is, each human has a gene that codes for eye color, etc), humans are not;genetically identical. Think of all the variation in the human population. We have different colors of hair, eyes;different heights, different tendencies towards disease, etc. One reason for the variation we see is that organisms, like;humans, might have different forms of genes, which we term alleles. These alleles code for different proteins, and;therefore result in the expression of different phenotypes.;A dominant allele is expressed phenotypically when present on either a single chromosome or on both homologous;chromosomes (that is, when its present on either the chromosome inherited from the mother, or the father, or both).;A recessive allele is masked by a dominant allele and is expressed only when paired with another recessive allele on the;Summer 2013;1;Genetics: Testing Hypotheses about Inheritance;homologous chromosomethat is, it is only expressed when the chromosomes inherited from both parents have the;recessive allele. A pair of identical alleles (AA or aa) at a genes locus represents the homozygous condition. Two;different alleles (Aa) at a genes locus represent the heterozygous condition. For example, eye color in humans is;determined by a single gene locus (although other loci can modify its effects). If the alleles at that locus are;homozygous dominant (AA) or heterozygous (Aa), the eyes will be brown. If the alleles are homozygous recessive (aa);the eyes will be blue. Alleles for brown eyes are said to be dominant over alleles for blue eyes.;How is genetic material passed on from generation to generation?;Alleles are passed on from parents to their offspring through reproduction, specifically through gametes (via meiosis);and fertilization. Meiosis is the process of cell division that happens only in sex cells and is responsible for creating;gametes (sperm and egg). Sperm and egg cells are unique from other body (somatic) cells in that each sperm or egg cell;contains exactly half of the genetic material from each parent. Why do you think this is the case?;To learn more about meiosis, please visit the Cells Alive site (http://www.cellsalive.com/meiosis.htm). Watch the;animations for the cell and as you do, track the locations of the chromosomes as they move through the phases of;meiosis. In addition, compare the beginning cells to the end products of meiosis. How many cells does meiosis begin;with? How many cells does meiosis end with? Are the numbers and types of chromosomes the same in both cases?;Drosophila are eukaryotic and diploid, having corresponding sets of genes on paired chromosomes. During each cross;the chromosomes containing the genes are shuffled by meiosis and combined at fertilization. Different mechanisms of;inheriting a trait involve different patterns of chromosomal movement during reproduction. The key to studying;genetics is to be able to predict the chromosomal movements that would result from different models for how a trait;might be inherited.;It is important to know that female Drosophila can store and utilize sperm from one insemination for a large part of;their reproductive lives. Therefore, only virgin females should be used in making the initial parental crosses. Females of;this species can mate six hours after they have emerged from the pupal case. If all adult flies are emptied from the;culture vial and the vial is left for six hours, all females removed the second time should be virgin. Males of any age may;be used in the crosses.;Using experiments to test patterns of inheritance;Modern genetics began with the experiments of Gregor Mendel, an Austrian monk with an inquisitive mind. Mendel;performed crosses between garden pea plants and discovered that certain alleles can mask one another (i.e. dominant;alleles mask recessive ones described earlier). A monohybrid cross is one in which the pattern of inheritance of a single;trait (e.g., pea shape) with a pair of alleles (e.g., round or wrinkled peas) is studied. In contrast, a dihybrid cross;involves parents that are identical except for two independent traits (e.g., pea color and shape).;Morgan built upon Mendels findings through his discovery that traits may be sex-linked, meaning the gene is carried;on a sex-determining chromosome (X or Y). In Drosophila, the X-chromosome carries sex-linked genes. So in flies;females have two copies of the X chromosome, and therefore carry two alleles of sex-linked genes, one on each X;chromosome. Male Drosophila, however, only have one X chromosome and therefore only carry one allele of a sexlinked gene. This means that whatever allele is passed on to males through their single X chromosome will be;expressed regardless of whether it is dominant or recessive. Since female flies inherit two alleles for sex-linked genes;expression of the alleles follows the dominant/recessive pattern described above. Any genes that are present on the;other chromosomesthat is, not on X or Y chromosomesare said to be autosomal. For example, all of Mendels pea;plant traits are inherited on autosomal chromosomes.;Alleles that are naturally common in the wild (e.g., red eyes in fruit flies) are known as wild-type alleles. Less common;alleles (e.g., white eyes in fruit flies) are known as mutant alleles. These are derived from characteristics that are;expressed naturally in the wild. Its important to note that wild-type alleles are not always dominant, nor are mutant;alleles always recessive.;Reciprocal crosses were important to Morgans discovery about sex-linked genes. A reciprocal set of crosses is;composed of a forward cross (where the male parent has the mutant allele and the female parent has the wild-type;allele) and a reverse cross (where the female parent has the mutant allele and the male parent has the wild-type allele).;Summer 2013;2;Genetics: Testing Hypotheses about Inheritance;For example, Morgans forward cross was a red-eyed (wild-type) female with a white-eyed (mutant) male. For the;reverse cross, Morgan used different flies with opposite alleles, in this case, a white-eyed (mutant) female and a redeyed (wild-type) male. The patterns of alleles in the offspring of these reciprocal crosses were markedly different and;as a result, Morgan was able to determine that the white eye-color allele in fruit flies was sex-linked.;In both Mendels and Morgans (who did experiments with fruit flies) experiments, it was important to begin with;parents that are said to be true breeding. This means that the parents are homozygous for the alleles of interest for;the study. Because the genetic makeup is known for the starting organisms, it enables scientists to track the genotypes;(or the genetic makeup of the organisms) through generations;Genetics with Computer Flies;All concepts about genetic information, the process of meiosis and experiments used to test for different patterns of;inheritance are identical to what was presented in the Drosophila. It is important to remember that all parental virtual;flies are true breeding and that there is no co-dominance or epistasis for any alleles being studied.;There are several key differences between living Drosophila and what we will be doing with the computer simulation.;The first difference is using virtual flies instead of live ones. These virtual flies are a new species we are naming;Drosophila spartaniensis. This species was created at MSU. The vast majority of the wild type individuals in the;population are small ~3 mm long, with red eyes, two straight wings that extend beyond the abdomen, a tan body, and;non-feathery antennae (just like the live wild type flies we have previously studied). Male flies are readily distinguished;from females in D. spartaniensis by having sex combs on their forelegs and having short, blunt abdomens with three;bands, whereas females have long, pointed abdomens with four bands.;The second difference is the mutant traits being studied. Since we have created these flies then any traits we will be;studying will be inherited in a variety of ways which may be different than a counterpart mutant trait in Drosophila;melanogaster.;The third difference is the instant life cycle. Whenever you mate the virtual flies, their offspring come up immediately;on the screen, there is no waiting for 2-weeks to see them. Dont forget that you still need to keep track of which;generation you are observing (e.g., parental or F1 or F2).;The fourth difference is the simultaneous viewing of both the forward and reverse crosses. This makes it a lot faster to;use your logic trees to deductively select the mode of inheritance for each mutant trait being studied. The disadvantage;is that you have a lot of flies on the screen at one time, and you have to make sure you are not mixing up the two;crosses nor missing any offspring which may be further down on the problem page.;The fifth difference is the method used to view the virtual flies (no need for the ether or tile or dissecting microscope).;You still have to carefully sex and describe the fly phenotype and to record all the counts.;Hypotheses about Modes of Inheritance;What weve learned about meiosis and genetics allows us to examine various alternative hypotheses (modes) about;how a particular allele might be inherited, and we can test their associated predictions by making crosses and;examining their resulting offspring. If the crosses are designed correctly, then each mode of inheritance will lead to a;distinctive phenotypic ratio in the offspring. We can choose among the alternative hypotheses by making statistical;comparisons between the observed phenotypic ratios (the evidence) with the expected ratios that are predicted by;each mode.;Here are four common modes that explain the inheritance of a single allele;1. Autosomal dominant;2. Autosomal recessive;3. Sex-linked dominant, and;4. Sex-linked recessive.;Below are some common modes that explain the inheritance of two alleles that are assorting independent of one;another in a dihybrid cross analysis;1. Both alleles are autosomal dominant;2. Both alleles are autosomal recessive;3. First allele is autosomal dominant while the second allele is autosomal recessive;Summer 2013;3;Genetics: Testing Hypotheses about Inheritance;There are also other modes that can be used to explain the inheritance of two alleles which are different than the ones;listed above;1. Both alleles are autosomal and located on the same chromosome (linked) [you still have to determine whether;each allele is dominant or recessive];2. One allele is autosomal while the other allele is sex-linked [you still have to determine whether each allele is;dominant or recessive];There are several ways to generate predictions from hypothesized modes of inheritance. We will use Punnett;rectangles because they are simple method and easy to remember. For the alleles we will study in lab, it is necessary to;predict the results both of parental crossesproducing the first (F1) generationand of F1 crossesproducing the;second (F2) generation. The predicted phenotypic ratios are converted to expected frequencies and will be used to;compare with the frequencies of real (or simulated) crosses to test your hypotheses.;Each mode of inheritance (i.e., alternative hypothesis) has a unique F2 generation prediction, and therefore the results;of experiments can be compared to the predicted value to determine how alleles are passed on from parents to;offspring. The best model will be the one whose predictions do not differ statistically from the actual cross values (do;not result in the null hypothesis being rejected). We will use the Chi-Square Goodness-of-Fit test to determine;whether or not our cross data actually matches our predictions.;What you will do;In todays lab, you will collect data to determine the mode of inheritance of traits in the virtual flies. You will observe;and record the parental flies phenotypes, then you will mate these flies to produce F1 offspring. Once these offspring;are phenotypically described and counted, then you will mate the F1s to generate the F2 offspring. As before, you will;record counts and phenotypes off the offspring (F2s). You will use the logic trees and Punnett rectangles to help you;select one mode of inheritance for the one trait being studied or for the two traits being studied. You will use the Chisquare goodness-of-fit statistical test to analyze the data and to arrive at the final conclusion for the inheritance pattern;for the trait(s) being studied.;Laboratory Objectives;As a result of participating in this exercise, you will;1. Make predictions for each mode of inheritance.;2. Practice using Punnett rectangles as predictive tools. Develop predictions for F2 offspring using Punnett;rectangles.;3. Mate, sex and describe virtual flies in LON-CAPA.;4. Perform reciprocal crosses using true breeding parents to generate F2 offspring.;5. Evaluate competing hypotheses about modes of inheritance using both virtual and real fly cross data.;6. Use the Chi-Square goodness-of fit test to evaluate support of the selected hypothesis(es).;7. Draw conclusions about modes of inheritance and hypothesis testing.;Methods;Engagement in Recitation;Part 1. Modeling Meiosis with Foam Cutouts of Chromosomes;Use the foam cutouts provided to model the action of chromosomes during the cell cycle of;1. Meiotic cells from Prophase 1 through Telophase 2;2. Filling in Punnett squares;Part 2. Developing a Logic Tree for Testing Hypotheses Involving One and Two Traits;Fill in before recitation, the sections in the appended section for Building Logic Tree a Single Trait. In groups, you;would work to create the logic tree for the single trait. At recitation, you will receive paperwork for Building a Logic;Tree for Determining Linkage.;Be sure to also find the appendix on-line which has more inheritance patterns Punnett rectangles to be used to derive;the predicted (expected) F2 phenotypic ratios which are needed for the Chi-square Goodness-of-Ft statistical testing.;Summer 2013;4;Genetics: Testing Hypotheses about Inheritance;Exploration during Lab;Part 3. Virtual Fly Problems in LON-CAPA;There will be one single practice problem page for each reciprocal cross (or experiment). In lab, you will be;expected to work in pairs. If you need to re-do the work at another time, you still have access to these pages, and;you can generate new data by clicking on the New Problem Variation button.;1.;Observe phenotypes, record data, perform each cross as indicated in the instructions that follow.;a. Set up one table for each cross (forward and reverse) to collect the data from each generation;(parents, F1 and F2). Make sure you have room to collect data for counts and all phenotypes (sex;eye color, wing characteristic, body color or antennae [if this is visible]);b. Recall that the wild type phenotype is red eyes, normal straight wings (longer than the abdomen);tan body color and non-feathery antennae (when present). This is just like D. melanogaster.;c. Select an experiment (practice problem).;d. You will see the parents for the forward cross and reverse cross. Collect all the data for the forward;cross in its own table. Next, carefully collect the data for the reverse cross in its own table.;e. To create parent cross, scroll down the page and type the word mate into the box provided and;click on Submit Answer.;f. To see the F1 offspring for each cross, scroll down the page. Collect the appropriate data in each;appropriate table. Be very careful not to mix up the male and females nor to mix up progeny;between each cross.;g. To create the F1 cross, scroll down the page and type the word mate into the box provided and click;on Submit Answer.;h. To view the F2 offspring for each cross, be sure to scroll down the page again. Collect the;appropriate data in each appropriate table. Be very careful not to mix up the male and females nor;to mix up progeny between each cross.;i. You do not have to type in the word done in the last box.;Table 1. Typical phenotypes of Drosophila;Character;Sex;Eye Color;Description;Male (short body with sex combs);Female (long body without sex combs);Red (Wild Type), Purple, Dwarf Red Eye;Sepia, or White;Body Color;Brown (Wild Type), Yellow, or Blackish Grey;Wings;See Figure 2;Figure 2. Drosophila wing phenotypes.;Summer 2013;5;Genetics: Testing Hypotheses about Inheritance;2.;Keeping all generation of the virtual flies on the screen, use your data and the logic tree to eliminate;hypotheses. Choose the hypothesis for the mode of inheritance that best predicts your data. Also, use the;following questions to help you eliminate hypotheses.;a. Looking at the parental generation, which specific mutant trait(s) is(are) being studied? Is this a;monohybrid or dihybrid cross analysis? Are there any hypotheses that can be eliminated now?;b. Looking at the F1 offspring in both the forward and reverse crosses, is the mutant trait autosomal or;sex-linked? Which additional hypotheses can be eliminated now?;c. Looking at the F1 offspring, is the mutant trait dominant or recessive? Which hypotheses can be;eliminated?;3.;Test your hypothesis using the Logic Trees and Chi-Square Goodness-of-Fit when there are more than 2;types of F2 offspring.;Assuming the hypothesis you put forth is supported, what is the expected value (ratio) of the F 2 offspring resulting;from this hypothesis? Explain your answers by using the Punnett square(s) that would produce this F2 offspring;phenotypes and ratios. Use the pages which are appended in this handout to come up with the expected ratios and;values for the F2 offspring for each mode of inheritance.;Using the Chi-Square Goodness-of-Fit Test for F2 Offspring;Do Chi-Square Goodness-of Fit analyses for both F2 offspring (forward or reverse) from each reciprocal cross. To;accomplish this, use tables similar to Table 1 for each cross and the expected ratios determined from the;appropriate Punnett rectangles.;Table 1. Example for how you might organize;Phenotype;Observed (O);Count;Expected (E);Count;2;Stat;calculations in your lab notebook or in a spreadsheet;(O-E);2;(O-E);2;(O-E) /E;Sum ();4.;Draw conclusions from the Logic Trees and Chi-Square test based on not rejecting the null hypothesis for;both the forward and reverse crosses. This means that if you have to reject the null hypothesis for either;cross then you have selected the wrong hypothesis and need to re-think your logic to choose another;hypothesis.;5.;Now start over at step 1 with a new reciprocal cross (experiment).;Explanation;Discuss in your groups;1. Why are reciprocal crosses helpful when trying to determine patterns of inheritance?;2. What hypotheses did you pose to test using a Chi-Square?;3. What were your conclusions from your Chi-Square?;4. Why are studying patterns of inheritance important?;Expand;Discuss in your group;1. How does meiosis link with what you did in lab today?;2. What are the limitations of meiosis? Advantages?;3. How does meiosis differ from mitosis? (link back to mitosis exercise);4. How does meiosis and what youve done today help explain why two siblings are never genetically identical;(unless they are identical twins)?;Summer 2013;6;Building a Logic Tree for a Single Trait;If the allele is autosomal dominant;Parental genotypes;Forward Cross;Male A / A Female + / +;Parental phenotypes;male mutant A and female wild type;Reverse Cross;Male + / + Female A / A;male wild type and female mutant A;Sperm genotypes;A;+;Ova genotypes;+;A;Punnett rectangle to generate F1 offspring;Ova Genotype;Ova Genotype;+;A;Sperm;Genotype;Sperm;Genotype;A;+;F1 offspring;F1 genotypes;F1 phenotypes;If the allele is autosomal recessive;Parental genotypes;Parental phenotypes;Forward Cross;Male a / a Female + / +;male mutant a and female wild type;Reverse Cross;Male + / + Female a / a;male wild type and female mutant a;Sperm genotypes;a;+;Ova genotypes;+;a;Punnett rectangle to generate F1 offspring;Ova Genotype;Ova Genotype;+;a;Sperm;Genotype;Sperm;Genotype;a;+;F1 offspring;F1 genotypes;F1 phenotypes;7;Building a Logic Tree for a Single Trait, continued;If the allele is sex-linked (X-linked) dominant;Forward Cross;Parental genotype;Male A / Y Female + / +;Parental phenotypes;Sperm genotypes;Reverse Cross;Male + / Y Female A / A;male mutant A and female wild type;male wild type and female mutant A;A and Y;Ova genotypes;+ and Y;+;A;Punnett rectangle to generate F1 offspring;Ova;Genotype;Ova;Genotype;+;A;Sperm;Genotypes;Sperm;Genotypes;A;Y;+;Y;F1 offspring;F1 genotypes;F1 phenotypes;If the allele is sex-linked (X-linked) recessive;Parental genotypes;Parental phenotypes;Sperm genotypes;Forward Cross;Male a / Y Female + / +;male mutant a and female wild type;Reverse Cross;Male + / Y Female a / a;male wild type and female mutant a;a and Y;+ and Y;+;a;Ova genotypes;Punnett rectangle to generate F1 offspring;Y;a;Sperm;Genotypes;a;Ova;Genotype;+;Sperm;Genotypes;Ova;Genotype;+;Y;F1 offspring;F1 genotypes;F1 phenotypes;8;Building a Logic Tree for a Single Trait, continued;How can you tell from looking at the F1 offspring whether or not a trait is autosomal or sex-linked?;If its autosomal, how can you tell from the F1 offspring whether the trait is dominant or recessive?;If its sex-linked (X-linked), how can you tell from the F 1 offspring whether the trait is dominant or recessive?;Write an efficient flowchart that shows logic (based on the work you did not theory) for deciding among the possible;modes of inheritance.;9;If both alleles are autosomal recessive and not linked;Forward Cross;Parental genotypes: Male a / a + / + Female + / + b / b;Reverse Cross;Male + / + b / b Female a / a + / +;Parental phenotypes: male mutant a and wild type;male wild type and mutant b;Female wild type and mutant b;Sperm genotypes;only a +;Ova genotypes;female mutant a and wild type;only + b;only + b;only a +;Punnett rectangle to generate F1 offspring;a;F1 offspring;F1 genotypes;Ova;Genotype;a +;Sperm;Genotype;s;Sperm;Genotype;s;Ova;Genotype;+ b;+;+ b;F1 male + / a b / +;F1 female + / a b / +;F1 phenotypes;Punnett rectangle to generate F2 offspring;Ova Genotype;a;+;+;+;a;b;Ova Genotype;+ b;a;+;+;a;b;a;a;a;b;+ b;b;+;+;+;+;Sperm Genotype;+;+;+ b;a;Sperm Genotype;+ b;+;F2 offspring;F2 genotypes;F2 phenotypes and ratio for each;10;If both alleles are autosomal recessive and linked;Forward Cross;Parental genotypes: Male a b / a b Female + + / + +;Reverse Cross;Male + + / + + Female a b / a b;Parental phenotypes: male mutant a and mutant b;male wild type and wild type;female wild type and wild type;female mutant a and mutant b;Sperm genotypes;a b only;+ + only;Ova genotypes;+ + only;a b only;Punnett rectangle to generate F1 offspring;ab;Sperm;Genotypes;Ova Genotype;++;Sperm;Genotypes;Ova Genotype;ab;++;F1 offspring;F1 genotypes;F1 male a b / + +;F1 female a b / + +;F1 phenotypes;Punnett rectangle to generate F2 offspring;Ova Genotype;ab;++;++;ab;Sperm;Genotype;Sperm;Genotype;ab;Ova Genotype;++;ab;++;F2 offspring;F2 genotypes;F2 phenotypes and ratio for each;11;Can you tell by looking at the parental generation will you be studying one or two mutant traits?;How can you tell from looking at the F1 offspring whether or not two autosomal traits are linked?;How can you tell from looking at the F2 offspring whether or not two autosomal traits are linked?;If two traits are sex-linked (X-linked) how can you tell whether they are linked to each other?;Write an efficient flowchart that shows logic for deciding among the possible linkage models.;12;If one allele is sex-linked recessive while the second allele is autosomal recessive and they are not linked;Forward Cross;Reverse Cross;Parental genotypes: Male a / Y + / + Female + / + b / b;Male + / Y b / b Female a / a + / +;Parental phenotypes: male mutant a and wild type;male wild type and mutant b;Female wild type and mutant b;Sperm genotypes;female mutant a and wild type;a + and Y +;+ b and Y b;only + b;only a +;Ova genotypes;Punnett rectangle to generate F1 offspring;a +;+;a;b;+;Y +;+;Y;b;+;Ova;Genotype;a +;+ b;F1 genotypes: female + / a b / +;Male + / Y b / +;F1 phenotypes: all females wild type and wild type;All males wild type and wild type;a;+;+;b;Y b;Sperm;Genotypes;Sperm;Genotypes;Ova;Genotype;+ b;a;Y;+;b;females a / + + / b;Male a / Y + / b;all females wild type and wild type;all males mutant a and wild type;Punnett rectangle to generate F2 offspring;Ova Genotype;Ova Genotype;+ +;+ b;a +;+ b;a b;+ b;+ +;+ b;+ b;+ b;+ +;a +;+ +;a b;+ +;+ +;+ +;+ b;+ +;Y +;a +;Y +;a b;Y +;+ +;Y +;+ b;Y +;Y b;a +;Y b;a b;Y b;+ +;Y b;+ b;Y b;F2 genotypes;see Punnett;F2 phenotypes and ratio for each;6 female wild type and wild type;2 females wild type and mutant b;3 males wild type and wild type;1 male wild type and mutant b;3 males mutant a and wild type;1 male mutant a and mutant b;a +;a b;+ +;+ b;a +;Sperm Genotype;a b;+ b;Sperm Genotype;a +;a +;a +;a b;a +;+ +;a +;+ b;a +;a b;a +;a b;a b;a b;+ +;a b;+ b;a b;Y +;a +;Y +;a b;Y +;+ +;Y +;+ b;Y +;Y b;a +;Y b;a b;Y b;+ +;Y b;+ b;Y b;see Punnett;F2 phenotypes and ratio for each;3 females wild type and wild type;1 female wild type and mutant b;3 females mutant a and wild type;1 female mutant a and mutant b;3 males wild type and wild type;1 male wild type and mutant b;3 males mutant a and wild type;1 male mutant a and mutant b;13;If both alleles are sex-linked (linked on the X-chromosome) and both recessive;Forward Cross;Reverse Cross;Parental genotypes;Male a b / Y Female + + / + +;Male + + / Y Female a b / a b;Parental phenotypes: male mutant a and mutant b;male wild type and wild type;Female wild type and wild type;Sperm genotypes;female mutant a and mutant b;a b and Y;only + +;Ova genotypes;+ + and Y;only a b;Punnett rectangle to generate F1 offspring;a b;Y;Ova;Genotype;a b;Sperm;Genotypes;Sperm;Genotypes;Ova;Genotype;+ +;+ +;Y;F1 genotypes;F1 phenotypes;Punnett rectangle to generate F2 offspring;Ova Genotype;Sperm Genotype;Sperm Genotype;Ova Genotype;F2 offspring;F2 genotypes;F2 phenotypes and ratio for each;14;Genetics Notation (materials adapted from Dr. Charles Elzinga;Genetics Terms 1;Phenotype;What allele(s) is(are);e.g.;Genotype;What alleles are;e.g., might have both round and wrinkled seed alleles;Homozygous;Same allele on;Heterozygous;Different alleles on;Hemizygous;1 allele on X, other chromosome is;r/Y, has r;Dominant allele;The allele expressed in;If Rr;Recessive allele;The allele hidden in;If Rr, r is;Sex Chromosome;Sex-determining;Mammals & fruit flies;Autosomal chromosomes;Chromosomes not involved in;HumansFruit fliesGenetics Terms 2;Autosomal Trait;Allele that is on;Sex-linked Trait;Allele that is on;Linked Traits;Alleles that are on the same chromosome and/or;Non-linked Traits;Alleles that are on different chromosomes or;Combining the Terms;Homozygous recessive?;Autosomal dominant trait?;Sex-linked recessive trait?;Using Drosophila Notation- Basics;The wildtype condition: Round eyes, red eyes, gray body, full-sized wings, small antennae;Each is symbolized with;Common mutations;Rod-shaped eyes, white eyes, brown eyes, black body, wingless, leg-like antennae;If mutation is dominant to wildtype, then symbolized with;If mutation is recessive to wildtype, then use;Drosophila Notation- Sex-linked Traits;Homozygous wild type female prune male;Notation;Male A;Y;x;female +;+

 

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