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25-460: The Punnett square is a square diagram that is used to predict the genotypes of a particular cross or breeding experiment. It is named after Reginald C. Punnett , who devised the approach in 1905. The diagram is used by biologists to determine the probability of an offspring having a particular genotype . The Punnett square is a tabular summary of possible combinations of maternal alleles with paternal alleles. These tables can be used to examine

50-439: A zygote , is seen when a combination of either two dominant or two recessive alleles code for the same trait. Recessive are always lowercase letters. For example, using 'A' as the representative character for each allele, a homozygous dominant pair's genotype would be depicted as 'AA', while homozygous recessive is shown as 'aa'. Heterozygosity, with hetero associated with different , can only be 'Aa' (the capital letter

75-493: A Punnett square, but the phenotype that may appear in the presence of a given genotype can in some instances be influenced by many other factors, as when polygenic inheritance and/or epigenetics are at work. Zygosity refers to the grade of similarity between the alleles that determine one specific trait in an organism . In its simplest form, a pair of alleles can be either homozygous or heterozygous . Homozygosity, with homo relating to same while zygous pertains to

100-402: A childhood bout of appendicitis, Punnett became acquainted with Jardine's Naturalist's Library and developed an interest in natural history. Punnett was educated at Clifton College . Attending Gonville and Caius College, Cambridge , Punnett earned a bachelor's degree in zoology in 1898 and a master's degree in 1901. Between these degrees he worked as a demonstrator and part-time lecturer at

125-699: A monograph, '"Mimicry" in Ceylon Butterflies, with a suggestion as to the nature of Polymorphism', in Spolia Zeylanica , the journal of the Colombo Museum, in which he voiced his opposition to gradualistic accounts of the evolution of mimicry which he later expanded on, in his 1915 book Mimicry in Butterflies . In 1910 Punnett became a professor of biology at Cambridge, and then the first Arthur Balfour Professor of Genetics when Bateson left in 1912. In

150-447: Is always presented first by convention). The phenotype of a homozygous dominant pair is 'A', or dominant , while the opposite is true for homozygous recessive . Heterozygous pairs always have a dominant phenotype. To a lesser degree, hemizygosity and nullizygosity can also be seen in gene pairs. "Mono-" means "one"; this cross indicates that the examination of a single trait. This could mean (for example) eye color. Each genetic locus

175-510: Is always represented by two letters. So in the case of eye color, say "B = Brown eyes" and "b = green eyes". In this example, both parents have the genotype Bb . For the example of eye color, this would mean they both have brown eyes. They can produce gametes that contain either the B or the b allele. (It is conventional in genetics to use capital letters to indicate dominant alleles and lower-case letters to indicate recessive alleles.) The probability of an individual offspring's having

200-487: Is now called the Punnett square , a square diagram that is used to predict the genotypes of a particular cross or breeding experiment, described for the first time in the 2nd edition of his book. In 1908, unable to explain how a dominant allele would not become fixed and ubiquitous in a population, Punnett introduced one of his problems to the mathematician G. H. Hardy , with whom he played cricket . Hardy went on to formulate

225-496: Is probably best remembered today as the creator of the Punnett square , a tool still used by biologists to predict the probability of possible genotypes of offspring. His Mendelism (1905) is sometimes said to have been the first textbook on genetics; it was probably the first popular science book to introduce genetics to the public. Reginald Punnett was born in 1875 in the town of Tonbridge in Kent, England. While recovering from

250-729: The Hardy–Weinberg principle , independently of the German Wilhelm Weinberg . Punnett was Superintendent of the Cambridge University Museum of Zoology from 1908 to 1909. In 1909 he went to Sri Lanka to meet Arthur Willey, FRS, then Director of the Colombo Museum and R H Lock , then Scientific Assistant at the Peradeniya Botanical Gardens and to catch butterflies. The following year, he published

275-498: The University of St. Andrews' Natural History Department. In October 1901, Punnett was back at Cambridge when he was elected to a Fellowship at Gonville and Caius College, working in zoology, primarily the study of worms, specifically nemerteans . It was during this time that he and William Bateson began a research collaboration, which lasted several years. When Punnett was an undergraduate, Gregor Mendel's work on inheritance

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300-488: The branching system) can also solve dihybrid and multi-hybrid crosses. A problem is converted to a series of monohybrid crosses, and the results are combined in a tree. However, a tree produces the same result as a Punnett square in less time and with more clarity. The example below assesses another double-heterozygote cross using RrYy x RrYy. As stated above, the phenotypic ratio is expected to be 9:3:3:1 if crossing unlinked genes from two double-heterozygotes. The genotypic ratio

325-515: The dominant allele for shape (round), while r represents the recessive allele (wrinkled). A represents the dominant allele for color (yellow), while a represents the recessive allele (green). If each plant has the genotype RrAa , and since the alleles for shape and color genes are independent, then they can produce four types of gametes with all possible combinations: RA , Ra , rA , and ra . Since dominant traits mask recessive traits (assuming no epistasis), there are nine combinations that have

350-429: The dominant phenotype for the other trait, and 1/16 are recessive for both traits. Valid only for Angiosperms or similar sexually reproducing organisms. This is assuming that Mendel's laws are followed. The expected phenotypic ratio of 9:3:3:1 can be broken down into: In the example pictured to the right, RRYY/rryy parents result in F 1 offspring that are heterozygous for both R and Y (RrYy). Another example

375-410: The genes are independent of each other, which means that having a particular allele of gene "A" does not alter the probability of possessing an allele of gene "B". This is equivalent to stating that the genes are not linked , so that the two genes do not tend to sort together during meiosis. The following example illustrates a dihybrid cross between two double-heterozygote pea plants. R represents

400-706: The genotype BB is 25%, Bb is 50%, and bb is 25%. The ratio of the phenotypes is 3:1, typical for a monohybrid cross . When assessing phenotype from this, "3" of the offspring have "Brown" eyes and only one offspring has "green" eyes. (3 are "B?" and 1 is "bb") The way in which the B and b alleles interact with each other to affect the appearance of the offspring depends on how the gene products ( proteins ) interact (see Mendelian inheritance ). This can include lethal effects and epistasis (where one allele masks another, regardless of dominant or recessive status). More complicated crosses can be made by looking at two or more genes. The Punnett square works, however, only if

425-502: The genotypical outcome probabilities of the offspring of a single trait (allele), or when crossing multiple traits from the parents. The Punnett square is a visual representation of Mendelian inheritance , a fundamental concept in genetics discovered by Gregor Mendel . For multiple traits, using the "forked-line method" is typically much easier than the Punnett square. Phenotypes may be predicted with at least better-than-chance accuracy using

450-420: The offspring to figure out inheritance of traits from 1856-1863. He first started looking at individual traits, but began to look at two distinct traits in the same plant. In his first experiment, he looked at the two distinct traits of pea color (yellow or green) and pea shape (round or wrinkled). He applied the same rules of a monohybrid cross to create the dihybrid cross. From these experiments, he determined

475-404: The phenotype round yellow, three that are round green, three that are wrinkled yellow, and one that is wrinkled green. The ratio 9:3:3:1 is the expected outcome when crossing two double-heterozygous parents with unlinked genes. Any other ratio indicates that something else has occurred (such as lethal alleles, epistasis, linked genes, etc.). The forked-line method (also known as the tree method and

500-408: The phenotypic ratio (9:3:3:1) seen in dihybrid cross for a heterozygous cross. Through these experiments, he was able to determine the basic law of independent assortment and law of dominance . The law of independent assortment states that traits controlled by different genes are going to be inherited independently of each other. Mendel was able to determine this law out because in his crosses he

525-598: The same year, Punnett was elected a Fellow of the Royal Society . He received the society's Darwin Medal in 1922. During World War I, Punnett successfully applied his expertise to the problem of the early determination of sex in chickens . Since only females were used for egg-production, early identification of male chicks, which were destroyed or separated for fattening, meant that limited animal-feed and other resources could be used more efficiently. Punnett's work in this area

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550-414: Was able to get all four possible phenotypes. The law of dominance states that if one dominant allele is inherited then the dominant phenotype will be expressed. The phenotypic ratio of a cross between two heterozygotes is 9:3:3:1, where 9/16 of the individuals possess the dominant phenotype for both traits, 3/16 of the individuals possess the dominant phenotype for one trait, 3/16 of the individuals possess

575-525: Was largely unknown and unappreciated by scientists. However, in 1900, Mendel's work was rediscovered by Carl Correns , Erich Tschermak von Seysenegg and Hugo de Vries . William Bateson became a proponent of Mendelian genetics and had Mendel's work translated into English. It was with Bateson that Reginald Punnett helped establish the new science of genetics at Cambridge. He, Bateson and Saunders co-discovered genetic linkage through experiments with chickens and sweet peas. In 1905 Punnett devised what

600-449: Was obtained in the diagram below, this diagram will have more branches than if only analyzing for phenotypic ratio. [REDACTED] [REDACTED] Reginald Punnett Reginald Crundall Punnett FRS ( / ˈ p ʌ n ɪ t / ; 20 June 1875 – 3 January 1967) was a British geneticist who co-founded, with William Bateson , the Journal of Genetics in 1910. Punnett

625-760: Was summarized in Heredity in Poultry (1923). With Michael Pease as his assistant, he created the first auto-sexing chicken breed, the Cambar, by transferring the barring gene of the Barred Rock to the Golden Campine . Reginald Punnett retired in 1940, and died at the age of 91 in 1967 in Bilbrook , Somerset . Dihybrid cross Gregor Mendel was an Austrian-Czech monk who bred peas plants in his monastery garden and compared

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