4 0 obj To compare ratios between linked and unlinked genes, we should first look at the chromosome segregation that occurs during meiosis.. For unlinked genes, two heterozygous parents, AaBb, where A and B are genes located on different chromosomes, will produce four types of gametes found in equal proportions (Fig. In such a case the test cross ratio should be 1:1 for parental phenotype: recombinants. Linked genes are carried on the same chromosome. The hypothesis that the two genes are unlinked predicts or unlinked that the offspring phenotypic ratio will be 1::1:. Genetic linkage. A testcross of the dihybrid for completely linked genes AaCc would result in a 1:1 . Linked genes sit closely together while unlinked genes sit farther apart. This is best illustrated by example. In criss-cross inheritance, an X-linked recessive gene is transmitted from P1 male parent (father) to F2 male progeny (grandsons) through its F1 heterozygous females (daughters), which are called carriers) and different F1 and F2 results (ratios) in the reciprocal crosses. Linked genes are the genes that are close to each other in the same chromosome. The genotypic array ratios for each gene is : Calculate and predict the genotypic and phenotypic ratios of offspring of dihybrid crosses involving unlinked autosomal genes. Science Biology Are the genes linked, unlinked, or incompletely linked? Can two genes not segregate independently? % The second law of Mendelian genetics discusses "independent assortment," which is typically how we think of genes behaving: flower petal color, plant height, pea size, etc. Phenotypic Ratios Linked Genes show unexpected phenotypic ratios. How do linked genes unlink? Closeness. Their patterns of inheritance cause genetic variation. Linked genes will tend to be inherited together and hence don't follow normal Mendelian inheritance for a dihybrid cross. If you scored the phenotypes of 20 offspring, and the A & C genes were unlinked, what phenotypes and in what ratios would you . The segregation of alleles into gametes can be influenced by linkage, in which genes that are located physically close to each . Genes 3 and 4 are linked. 2).The four combinations of gametes are AB, Ab, aB, ab . For clarity, it is worth repeating that the above table applies only to linked markers. View Homework Help - Homework 4-unlinked and linked genes-KEY.pdf from GEN GEN-604 at University of New Hampshire. They are especially easy to use for determining fit to various ratios: e.g., for a 1:1 ratio, the 2 formula becomes: 2 1 12 One such experiment was performed by Bateson and Punnett with sweet peas. Question 4. answer choices. <>/ExtGState<>/XObject<>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/Annots[ 10 0 R 13 0 R 14 0 R 15 0 R 16 0 R 17 0 R 18 0 R 19 0 R 20 0 R 21 0 R 22 0 R 23 0 R 24 0 R 25 0 R 26 0 R 27 0 R 33 0 R] /MediaBox[ 0 0 612 792] /Contents 4 0 R/Group<>/Tabs/S/StructParents 0>> Or, they can be so close together that they almost never separate. Instead the phenotypic ratio will be more closely aligned to a monohybrid cross as the two . compliment each other well. When the sister chromatids of the homologous chromosomes align together during the metaphase, the DNA strands of them can break and rejoin, swapping large parts of the chromosomes. 3. 7 How are linked genes expressed in the offspring? 2. 1. Getting back to linked markers, remember that single crossovers give rise to 100% T outcomes. Linked genes are "stuck together" like your sleeve is to your shirt: This 9:3:3:1 phenotypic ratio is the classic Mendelian ratio for a . The two dominant alleles are linked on one chromosome, and the two recessive . What is the ratio for unlinked genes? What are Unlinked Genes Definition, Location, Inheritance 3. To log in and use all the features of Khan Academy, please enable JavaScript in your browser. 1:01 4. no correct answer 5. At 50 cM the recombination rate is 50%, which means the expected 1:1:1:1 ratio for unlinked genes is observed. (1) "If two genes are linked, then the expected phenotypic ratio resulting from a testcross would be" 1. Email. What is the Difference Between Linked and Unlinked Genes Comparison of Key Differences, Chromosomes, Homologous Recombination, Inheritance, Linked Genes, Unlinked Genes. Phenotypic Ratios Linked Genes show unexpected phenotypic ratios. determine whether genes are unlinked or likely to be linked. . Thus, only unlinked genes follow Mendels second law. The main difference between linked and unlinked genes is that the linked genes sit close together in the chromosomewhereas the unlinked genes sit farther away from each other in the chromosome. Summary Linked vs Unlinked Genes. 1 0 obj Genes on separate chromosomes, such as Gene 5 and Gene 6, are never linked (bottom illustration). Genes with a recombination frequency of 50 % is considered to be linked. Linked Genes On The Same Chromosome Exhibit Distorted Mendelian Ratios. stream Pairs of alleles are inherited independently of one another if their gene loci are on separate chromosomes (these genes are unlinked). Genes, in this case, are not passed on independent of another gene. Heterozygous test cross of linked genes = 1 : 1 : 0.1 : 01 phenotypic ratio (uncommon phenotypes are recombinants). X-linked inheritance. 10. This is known as a genetic linkage. How are linked genes expressed in the offspring? Answer (1 of 4): It depends whether or not they are on the same chromosome. Bear in mind that when you're talking about linked genes, you must be talking about the relationships between two genes; it doesn't make sense to talk about a single gene being linked or unlinked. all based off of genetic linkage. Explain why linked genes do not assort independently. 3 0 obj If genes are close together, the chances of being recombined are higher than if they . Donate or volunteer today! Therefore, they have a higher chance to undergo homologous recombination, which allows the separation of the unlinked genes to different gametes. Whats the difference between linked and unlinked genes? Unlinked APK: Free Download the Latest Version (UPDATED 2022) Unlinked APK is a famous app downloading platform, and It was launched after the Filelinked App. {e]}\= Thus, in order to be separated by homologous recombination, a particular gene pair should be in a considerable distance in the chromosome. How to Market Your Business with Webinars? The area that crosses over and momentarily connects is called the chiasmata. Map units indicate relative distance and order, not precise locations of gene. Unlinked Genes. Pedigree for determining probability of exhibiting sex linked recessive trait, Inheritance of mitochondrial and chloroplast DNA, Biology is brought to you with support from the Amgen Foundation. A chromosome possesses many genes & all genes present in the chromosome are inherited together. At 50 cM the recombination rate is 50%, which means the expected 1:1:1:1 ratio for unlinked genes is observed. | EduRev NEET Question is disucussed on EduRev Study Group by 141 NEET Students. This can be used to analyze the results of test cross to determine the significance of any variation. Moreover, in linked genes, the chance of inheriting together is more than 50%. Linked and unlinked genes can be easily known from breeding experiments. Linked Genes.svg. the alleles for the linked genes do not segregate during the formation of gametes. Therefore, linked genes are more prone to be inherited together during the formation of gametes. they assort independently and are said to be unlinked. If a normal dihybrid cross results in an unexpected ratio, it indicates the . However, the chance of unlinked genes to be inherited together is 50%. Inheritance of X-Linked Recessive Genes. Generally, a single chromosome contains thousands of genes and some gene pairs are close to each other while the distance between the other gene pairs may be high. <>>> How do you know if the genes are linked? When genes are unlinked, they have a recombination frequency of 0.5, which means 50 percent of offspring are recombinants and the other 50 percent are parental types. The Expected Genotypic and Phenotypic Arrays of two unlinked genes considered jointly are the product of the separate Genotypic and Phenotypic Arrays. What is the dihybrid ratio of linked and unlinked genes? Unlinked genes appear to segregate and show independent assortment. Genes on different chromosomes assort independently giving a 1: 1: 1: 1 test cross ratio. The chromosomal basis of inheritance. Oct 16,2022 - Ratio of linked & unlinked genes in dihybrid.? Genetic Linkage.Learn.Genetics, University of Utah, 2 Dec. 2014,Available Here, 1. We are not permitting internet traffic to Byjus website from countries within European Union at this time. Therefore, the main difference between linked and unlinked genes is the distance and the patterns of inheritance. Genes which are located on different chromosomes or genes that are farther away from each other are known as unlinked genes. Refresh the page or contact the site owner to request access. In short, whenever two genes are linked because of their location on a chromosome, their alleles will not segregate independently during gamete formation. are on chromosomes close together. 30 seconds. Linked genes are found very closely on the same chromosome. The results in the datatable are from a simulated dihybrid of testros progeny in order to see whether two genes are linked testcross. After classifying each rRNA gene pair as linked or unlinked based on the distance between the 16S and 23S rRNA genes, we found that 3.65% of the genomes in our dataset had exclusively unlinked rRNA genes, 0.62% had mixed rRNA gene status (i.e. If genes are linked together, then Mendel's law of independent assortment does not apply. eeVwMdlSvZb~L~~-fm/9>~c[xL??-|YNe|67Y,Ece%ky)G~wOiH~Xo&y=>3M^(mbVB=^$\rzDy!MDwLFsu78_[=a.:c%g$fWoPj/mrJVT Linked genes can become unlinked during recombination; the probability of genes separating depends on their distance from each other. Furthermore, linked genes do not undergo homologous recombination while unlinked genes undergo homologous recombination. To determine whether the introduced genes were genet-ically linked or unlinked in the T1 progeny, T2 seeds from co-transformed rapeseed and tobacco lines were germi- . ncD%De#C8TPQvl\^f1-YDcDeyOW%Yues%qS&ZG SD}(=qJ9)AH`kqfRQOVa|paW:!0 G|Gf[v[ #Z@Y1 Y What is the difference between linked and unlinked genes? A testcross of the dihybrid for unlinked genes, AaBb, would result in a 1:1:1:1 phenotypic ratio. Genes that are located on separate, non-homologous chromosomes will always sort independently. 1 YyRr yellow, round seeds 1 Yyrr yellow, wrinkled seeds 1 yyRr green, round seed 1 yyrr green, wrinkled seeds If two genes are unlinked we expect to see 1:1:1:1 ratio in the progeny of the test cross (50% parental phenotype and 50% recombinant phenotype) Parental type Parental type . Home Science Biology Genetics What is the Difference Between Linked and Unlinked Genes. What is the ratio for unlinked genes? . Requested URL: byjus.com/biology/difference-between-linked-and-unlinked-genes/, User-Agent: Mozilla/5.0 (iPad; CPU OS 15_5 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) GSA/219.0.457350353 Mobile/15E148 Safari/604.1. are on the same chromosome. The genes which are located on the same chromosome and are likely to be inherited together are known as linked genes. Description. Genes are the specific DNA sequences in chromosomes. Linked Genes . Multiple crossovers can result if the loci are located on the same chromosome far from each other. Unlinked Genes follows expected ratios 9:3:3:1. Each gamete gets a single copy, determined at random, of each chromosome. Linkage: Study of inheritance of all genes present in a chromosome together.. All genes in a chromosome are together referred as linked genes & they form a linkage group. Google Classroom Facebook Twitter. Question 5. If you're seeing this message, it means we're having trouble loading external resources on our website. Linked Genes Definition. 11 Chi square test pinpoints the probability that ratios are evidence of linkage! Complete Linkage. . Linked genes occur on the same chromosome, therefore, tend to be inherited together (i.e., do not segregate independently). Unlinked Genes and Linked Genes. The null hypothesis specified that the genes are unlinked. We now have a gene unit measurement for two linked genes. . What are the Similarities Between Linked and Unlinked Genes Outline of Common Features 4. Hence, this process is called gene mapping. The unlinked genes are less likely to be inherited together. Answer: Dihybrid Cross A dihybrid cross determines the allele combinations of offspring for two particular genes that are unlinked (not on the same chromosome) Because there are two genes with two alleles per gene (multiple alleles not required), there can be up to four different gamete combina. Linked genes tend to be inherited together, like freckles and red hair, because they - - -. Usually linkage group as a whole passes into gamete during gametogenesis and are inherited together. The reason behind this type of inheritance is the inability of these genes to undergo homologous recombination. If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked. In this article, we propose an X-linked hypothesis of brain disorders that postulates a neuronal origin of those neurodegenerative and psychiatric disorders with a greater male prevalence. . What is the test cross ratio for unlinked genes? They can cause genetic variation through homologous recombination. X-linked gene: 4: F 2 cross - two unlinked autosomal genes: 5: F 2 cross - one autosomal - one X-linked gene: 6: Linkage - Coupling and Repulsion: 7: F 2 cross - two linked autosomal genes -coupling: 8 F 2 cross - two linked autosomal genes . Unlinked genes show independent assortment, a di-hybrid ratio of 9: 3: 3: 1 and the di-hybrid or double test cross ratio of 1: 1: 1: 1 with two parental and two recombinant types. Types of Linkage. 1:02:01 (2) The penetrance and expressivity of. Our mission is to provide a free, world-class education to anyone, anywhere. Genes with a recombination frequency of 50 % is considered to be linked. Given the large number of host proteins required for HIV-1 replication and the increasing understanding of how their . ; The total number of linkage group in an organism is equal to its haploid number of chromosomes. Linkage. Linked genes are always expressed together in an offspring since linked genes are not assorted independently during cell division. Where are unlinked genes located on a chromosome? These genes separate independently from each other during the formation of gametes. When genes are close together on the same chromosome, they are said to be linked. 2 What is the test cross ratio for unlinked genes? Key Difference - Linked vs Unlinked Genes . Besides, the dihybrid ratio of linked genes is 3:1 while the dihybrid ratio of unlinked genes is 9:3:3:1. However, that gives us two random points on a chromosome. Furthermore, linked genes have a chance to be inherited together while unlinked genes are more likely to separate during the formation of gametes in a process known as homologous recombination. e Iu1Z 6. Hence the ratio of 9:3:3:1 of phenotypes. Unlinked genes are the genes situated in different chromosomes or far away on the same chromosomes and are inherited independently. 3 What does a 3 1 ratio mean in genetics? They performed a typical dihybrid cross between one pure line with purple flowers and long . The last step is to use a third gene, look at the ratio between all of them. #3. However, if the genes are linked, this expected ratio changes due to the failure of independent assortment of alleles. On the other hand, unlinked genes occur farther apart in a particular chromosome or in different chromosomes. endobj endobj . A 3:1 Ratio is the relative fraction of phenotypes among progeny (offspring) results following mating between two heterozygotes, where each parent possesses one dominant allele (e.g., A) and one recessive allele (e.g., a) at the genetic locus in questionthe resulting progeny on average consist of one AA genotype (A . Science. Besides, the dihybrid ratio of linked genes is 3:1 while the dihybrid ratio of unlinked genes is 9:3:3:1. Hence, linked genes have a high chance to be inherited together. Whereas genes located on different chromosomes assort independently and have a recombination frequency of 50%, linked genes have a recombination frequency that is less than 50%. Linked genes areinherited together while unlinked genes have a less chance to be inherited together. However, each chromosome contains hundreds or thousands of genes, organized linearly on chromosomes like beads on a string. Also bear in mind that . AP is a registered trademark of the College Board, which has not reviewed this resource. What is the Difference Between Heterosis and What is the Difference Between Male and Man, What is the Difference Between Penicillin G and Penicillin V, What is the Difference Between Mezcal and Tequila, What is the Difference Between Lutein and Zeaxanthin, What is the Difference Between Effector and Memory Cells, What is the Difference Between LinkedIn and Twitter. Distinguish between: autosome = non-sex chromosomes; in humans, chromosomes 1 through 22. sex chromosomes = those chromosomes which help determine the sex of an individual; in humans, the X and Y chromosomes. No tracking or performance measurement cookies were served with this page. Occasionally during meiosis, the homologous chromosomes will cross-over and exchange information by their chromatids breaking up and reforming. This is the main difference between linked and unlinked genes. In contrast, in unlinked genes, the chance of inheriting together is less than or equal 50%. Linked and unlinked genes are the two types of genes in the genome. Both inherit to the gametes during the sexual reproduction. . Among the F2 progeny, there are more parental types than recombinant types. Genes with a recombination frequency of 50 % is considered to be linked. 5. English: Linked genes are not independently assorted and do not follow Mendelian dihybrid ratios. 1. If the two traits are unlinked and the F1-plants are self-fertilized, in the F2 generation plants we expect the 9:3:3:1 ratio of offspring: 9/16 tall plants with spherical seeds . 2 INHERITANCE Genes may be linked or unlinked and are inherited accordingly. Last Update: October 15, 2022. . Sex-linked genes are located on a sex chromosome, and X-linked genes are located on the X chromosome. nome relative to each other. In dihybrid crosses, departures from a 1:1:1:1 ratio of F1 gametes indicate that the two genes are on the same chromosome "Ex 1: For AaBb, four gametes = AB, Ab, aB, ab = 1:1:1:1 thus . Genetic linkage of these genes can be identified by test crosses and is measured by centimorgan (cM). Heterozygous test cross of unlinked genes = 1 : 1 : 1 : 1 phenotypic ratio. If two genes are inherited together more than the 50% of the time, then these two genes are linked genes. Heterozygous test cross of unlinked genes = 1 : 1 : 1 : 1 phenotypic ratio Heterozygous test cross of linked genes = 1 : 1 : 0.1 : 01 phenotypic ratio (uncommon phenotypes are recombinants) A dihybrid cross is a cross between two individuals that shows the inheritance of two different genes at the same time; usually involving unlinked autosomal . Unlinked Genes are independently assorted and will follow a dihybrid pattern. <> . This is also a difference between linked and unlinked genes. The further apart the chromosomes are located, the more likely. 3. Unlinked Genes are located on different chromosomes. Linked genes tend to be inherited together because they are located on the same chromosome. What are genes with linked loci? Due to their close proximity, they do not show independent assortment as mentioned in Mendels second law. Homework 4 - GEN 604 - DUE in lecture on Sept. 23, 2019 KEY Inheritance of Two . Chromosome Theory of Linkage. The main intention of developing this app is to facilitate users to download any app from one place. Based on the patterns of inheritance of genes, scientists can create maps of genes, revealing the relative distances between genes. two genes each segregating 3:1--->9:3:3:1--can be analyzed in exactly the same way. 1:1:1:1 3. If genes are located far enough apart on a chromosome, crossing over will occur often enough that the genes assort independently. Linked vs Unlinked Genes. t)~|5%.5e'E D8 bIbo Xv 6 What is the dihybrid ratio of linked and unlinked genes? Distinguish between linked genes and sex-linked genes. The key difference between linked and unlinked genes is that linked genes do not segregate independently while unlinked genes are able to assort independently during the cell division. Example: Consider two genes A and B each with two alleles - A 1 & A 2: B 1 & B 2. Degenerate bssA primers and inverse PCR were used to amplify two unlinked . Variations on Mendel's laws (overview) Thomas Hunt Morgan and fruit flies. The gene located in different chromosome are unlinked genes. This situation occurs in two instances: either when the genes are on completely different chromosomes, or when they are far enough apart on a single chromosome that the crossovers are so numerous that the alleles . Khan Academy is a 501(c)(3) nonprofit organization. There are 46 chromosomes in the human genome. Another important difference between linked and unlinked genes is that linked genes do not follow Mendels second law while unlinked genes follow Mendels second law. Genes may be unlinked if they are on separate chromosomes or are placed far on the same chromosome. Mendel's second law of genetics is the Law of Independent Assortment, which holds that two different genes will be independently sorted into gametes, . Understanding: A linkage group is a group of genes whose loci are on the same chromosome and hence don't independently assort. Special cases of the 2 formula for a family segregating into two classes are given by Mather. . Types of Linkage: Linkage is of two types, complete . Biology questions and answers. Di-hybrid ratio of two Linked genes. endobj What it means for genes to be linked. Linked and unlinked genes are the two types of genes in the genome. tend to be adaptations best suited for the environments of the organism. Consider two Drosophila genes linked to the X-chromosome, the eye color gene white and a body color gene yellow. When two heterozygotes are mated in a normal dihybrid cross with independent assortment of alleles, the expected ratio in the offspring is 9:3:3:1. . Explanation: If both parents are heterogeneous for both traits the ratio of phenotypes is the ratio of 9:3:3:1. There will be a random and even distribution of gamete types, and an RF of 0.50 is the expectation. When genes are close together on the same chromosome, . Linked genes are the genes that are situated closely on the same chromosome and are likely to be inherited together to offspring. Why do linked genes not assort independently? When two genes are close together on the same chromosome, they do not assort independently and are said to be linked. Multiple crossovers can result if the loci are located on . At 50 cM the recombination rate is 50%, which means the expected 1:1:1:1 ratio for unlinked genes is observed. In Drosophila, white eyes (w) and vestigial wings (vg) are recessive to red eyes and wildtype wings (w+ and vg+). Determining linkage through chi square analysis. . Conclusion Remember: Recombination frequency "maxes out" at 50% (meaning the genes being unlinked, or assorting . 2 = (O-E)2 / E. Then, these rearranged homologous chromosomes separate into gametes. In addition, most organisms are diploid and they contain two chromosomes with the same arrangement of genes, the homologous chromosomes. The hypo. But, two genes can be really far apart on the same chromosome, and they get split apart so often by chance that they assort almost independently. Linked genes occur in close proximity on a particular chromosome. <> Middle school Earth and space science - NGSS, World History Project - Origins to the Present, World History Project - 1750 to the Present. What are Linked Genes Definition, Location, Inheritance 2. Linked genes sit . genomes with multiple rRNA copies that had at least one set of unlinked rRNA genes and at least one . Genes may be unlinked if they are on separate chromosomes or are placed far on the same chromosome. Biology. Hence, this explains the fundamental difference between linked and unlinked genes. Compensatory variation in related genes may have arisen evolutionarily, such that a deleterious variant in one gene may show significant association with an unlinked compensatory variant in a functionally related gene 61. Linked genes are genes that are likely to be inherited together because they are physically close to one another on the same chromosome. It was not long from the time that Mendel's work was rediscovered that new anomalous ratio began appearing. by random chance, two unlinked genes will be inherited . When genes are perfectly linked, they have a recombination frequency of 0. Also, both their patterns of inheritance cause genetic variation. During the formation of gametes, DNA replicates and the centromere holds the sister chromatids of each chromosome. In addition, the test cross ratio of linked in genes in a dihybrid cross is 1:1 while the test cross ratio of unlinked genes in a dihybrid cross is 1:1:1:1. The. We use cookies to ensure that we give you the best experience on our website. Fuel analysis revealed that the ULSDs differed based on the ratio of low to high molecular weight (LMW/HMW) n-alkanes. Unlinked Genes follows expected ratios 9:3:3:1 Summary - Linked vs Unlinked Genes Linked genes are found very closely on the same chromosome. Gene Linkage For unlinked genes, any combination of traits can potentially occur in offspring This is due to the independent assortment of chromosomes during meiosis For linked genes, only parental phenotypes commonly occur in the offspring Recombinant phenotypes can occur, but only when crossing over occurs Hence, phenotypic ratios of offspring can be used to determine if genes are . LaurenMCAT said: Simply: they do NOT sort independently. DCOs, as stated above, give rise to P:N:T in a 1:1:2 ratio. Therefore, Unlinked APK has gained popularity as an essential app to get all apps and . These genes cannot be assorted independently during the meiosis. Chromosome Linked Genes are located on the same chromosome. Using this ratio How These Experiments Are Done if genes are unlinked and calculate the . Drosophila Gene Linkage Map By Twaanders17 Own work (CC BY-SA 4.0) via Commons Wikimedia2. Measuring gene map with linked genes. This is due to the ability of these genes to undergo homologous recombination. How are linked genes expressed in the offspring? An Insight into Coupons and a Secret Bonus, Organic Hacks to Tweak Audio Recording for Videos Production, Bring Back Life to Your Graphic Images- Used Best Graphic Design Software, New Google Update and Future of Interstitial Ads. Between a heterozygote X homozygote parent if a normal dihybrid cross between one pure line with purple flowers and.. Ratio should be in a 1:1:1:1 phenotypic ratio will resemble a monohybrid cross as the two types complete. Genes sit farther apart the segregation of alleles into gametes, that gives us two points. T follow normal Mendelian inheritance for a pair of genes the chromosome are unlinked unlinked Among progeny suggest one gene is involved in the genome rearranged homologous.. 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Two classes are given by Mather filter, please make sure that the genes situated in chromosome. Give you the best experience on our website pair of genes in eukaryotes meaning! Bssa primers and inverse PCR were used to analyze the results of test to ; Question: Genetic linkage 1 of Utah, 2 Dec. 2014, Available Here, 1 besides! Than 50 linked and unlinked genes ratios main intention of developing this app is to use this site we assume. If genes are genes that are Driving the Vehicle Industry Forward > Solved linkage Assorted and do not separate during the formation of gametes are AB AB! Located in different chromosomes ratio will be 1: 1 phenotypic ratio will be more closely aligned to monohybrid. Gene is involved in the phenotype which would involve a cross between one line Genes AaCc would result in a 1:1:1:1 phenotypic ratio is the classic Mendelian ratio for activity of the genes! 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