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Punnett Squares

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elmira mccomb

on 31 May 2011

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Transcript of Punnett Squares

Punnett Square : a mathematical tool used by genecticists to show allelic combinations of genetics to predict offspring ratios. What is a Punnett Square B b b b Bb bb Bb bb Genotype: 2Bb; 2bb Phenotype: 50% Brown eyes
50% Blue eyes In humans, brown eyes (B) are dominant over blue (b). A brown-eyed man marries a blue-eyed woman and they have three children, two of whom are brown-eyed and one of whom is blue-eyed. Draw the Punnett square that illustrates this marriage. What is the genotype and phenotype? Parts of a Punnett Square Ex. Genotype: The Genotype is determined at the results of the punnet square. A genotype is the actual physical material made up of DNA that was passed to the organism by its parent. For example if your punnet square has X's to represent the different traits on the actual square, then you count up the number of similar pairs of X's and you mark those your genotypes. Phenotype: The phenotype is the description of the physical and behavioral charateristics of the organism. This can be found usually beneath the genotype; the phenotype is shown in percentage instead of numbers and has the clear name of the trait that the lettering in the genotype it represents.
Ex. 50% brown eyes; 50% blue eyes Complete Dominance: This is the kind of dominant gene that completely masks effect of the reccessive in heterzygous condition. So the result creates a dominant trait because it has a dominant allele
Ex. Tt; Bb Incomplete Dominance: This is when there are two heterozygouse traits put together, but the end result is neither the reccessive or dominant trait. This produces a hibrid of both the dominant and reccessive trait.
Ex. A homozygous white Snapdragon flower crossed with a homozygous red Snapdragon flower, but the offspring is a pink Snapdragon flower. How to Create a Punnett Square Click play Your Turn Directions: Fill in the punnet square with, using option box on the right on a seperate sheet of paper. When finshed click the circle in each box to check your answer. A. D B. d C. d D. d E. dd F. Dd G. dd H. Dd Opitions: A. D B. d D. d C. d E. dd F. Dd G. dd H. Dd Ex. One cat carries heterozygous, long-haired traits (Dd), and its partner carries homozygous short-haired traits (dd). Use a Punnett square to determine the probability of one of their offspring having long hair. Long hair cat Short hair cat History of the Punnett Square This is one of the founder of the punnet square, his name is Reginald Crundall Punnett. Encyclopedia
Professor Reginald Crundall Punnett FRS (20 June 1875 – 3 January 1967) was a British geneticist who co-founded, with William Bateson, the Journal of Genetics in 1910. Punnett 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.
Life and work

Reginald Punnett was born in 1875 in the town of Tonbridge in Kent, England
. While recovering from 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 at the University of Cambridge, Punnett earned a degree in zoology in 1898, and a masters in 1902. Between these degrees he worked as a demonstrator and part-time lecturer at the University of St. Andrew's Natural History Department. However, by 1902 Punnett was back at Cambridge 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 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 established the new science of genetics at Cambridge. He and Bateson co-discovered genetic linkage through experiments with chickens and pea plants.

In 1908, unable to explain how a dominant gene 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 the Hardy-Weinberg principle, independently of the German Wilhelm Weinberg.

In 1910 Punnett became professor of biology at Cambridge, and then the first Arthur Balfour Professor of Genetics when Bateson left in 1912. In 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 gender 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 was summarized in Heredity in Poultry (1923).

Reginald Punnett retired in 1940, and died at the age of 91 in 1967 in Bilbrook, Somerset. Link to website This the second founder of the punnet square and his name is William Bateson. Codominance: This occurs when both alleles for a gene are expressed in a heterozygous offspring. Ex. Dihybrid Cross: This is a cross in which two characteristics are tracked. The offspring of a dihybrid cross are called dihybrids. Ex. This is a chart of a dihybrid cross heterozygous dominance in eye color.
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