Dihybrid cross: Difference between revisions
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A '''dihybrid cross''' is a cross between [[F1 hybrid|F1]] offspring (first generation offspring) of two [[individuals]] that differ in two [[traits]] of particular interest. For example: RRyy/rrYY or RRYY/rryy parents result in F1 offspring that are heterozygous for both R & Y. |
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== YOOOOOOOOOOUUUU SUUUUUUCKKKKKK == |
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A dihybrid cross is often used to test for dominant and recessive [[genes]] in two separate characteristics. Such a cross has a variety of uses in [[Mendelian inheritance|Mendelian genetics]]. |
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[[Meiosis]] is the cellular process of [[gamete]] creation, it is where sperm and eggs get the unique set of genetic information that will be used in the development and growth of the offspring of the mating. The rules of meiosis as they apply to the dihybrid are codified in [[Law of Segregation|Mendel's First Law]] and [[Law of Independent Assortment|Mendel's Second Law]] also called the [[Law of Segregation]] and the [[Law of Independent Assortment]]. |
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For genes on separate [[chromosomes]] each [[allele]] pair shows independent segregation. If the first filial generation (F1 generation) produces four offspring, the second filial generation, which occurs by crossing the members of the first filial generation, shows a [[phenotype|phenotypic]] (appearance) ratio of 9:3:3:1. |
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== Mendel's Dihybrid Cross == |
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Mendel crossed pure breeding plants with round seeds and yellow albumen to pure breeding plants with wrinkled seeds and green albumen. The F1 plants all had round seeds and yellow albumen and Mendel predicted that they would be heterozygous for both traits (RrYy). |
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He then did a self-cross of the F1 plants to produce the results shown as the F2. He predicted that the plants with round seeds and yellow albumen would be of four genotypes in the specific ratio of 1 RRYY : 2 RRYy : 2 RrYY : 4 RrYy. And he made similar predictions for the plants with round seeds and green albumen and the ones with wrinkled seeds and yellow albumen. |
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In order to test his prediction of more than one genotype within a phenotypic category in the F2, he allowed the F2 plants to self-cross and he recorded how many of the plants bred true or showed segregation for one or both of the characters. This is shown in the F3 data. The observed numbers of phentoypic types matches the predicted ratios. |
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== Punnett square for a Dihybrid Cross == |
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In the [[pea]] plant, two characteristics for the peas, shape and color, will be used to demonstrate an example of a dihybrid cross in a [[punnett square]]. '''R''' is the dominant gene for roundness for shape, with lower-case '''r''' to stand for the recessive wrinkled shape. '''Y''' stands for the dominant yellow pea, and lower-case '''y''' stands for the recessive green color. By using a punnett square (parents RrYy x RrYy; making the [[gametes]] are '''RY''', '''Ry''', '''rY''', and '''ry'''): |
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{| class="wikitable" width="40%" |
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|- |
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| width=12% align="center" | |
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| width=22% align="center" | '''RY''' |
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| width=22% align="center" | '''Ry''' |
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| width=22% align="center" | '''rY''' |
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| width=22% align="center" | '''ry''' |
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|- |
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| width=12% align="center" | '''RY''' |
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| width=22% align="center" bgcolor="yellow" | RRYY |
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| width=22% align="center" bgcolor="yellow" | RRYy |
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| width=22% align="center" bgcolor="yellow" | RrYY |
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| width=22% align="center" bgcolor="yellow" | RrYy |
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|- |
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| width=12% align="center" | '''Ry''' |
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| width=22% align="center" bgcolor="yellow" | RRYy |
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| width=22% align="center" bgcolor="green" | RRyy |
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| width=22% align="center" bgcolor="yellow" | RrYy |
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| width=22% align="center" bgcolor="green" | Rryy |
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|- |
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| width=12% align="center" | '''rY''' |
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| width=22% align="center" bgcolor="yellow" | RrYY |
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| width=22% align="center" bgcolor="yellow" | RrYy |
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| width=22% align="center" bgcolor="red" | rrYY |
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| width=22% align="center" bgcolor="red" | rrYy |
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|- |
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| width=12% align="center" | '''ry''' |
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| width=22% align="center" bgcolor="yellow" | RrYy |
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| width=22% align="center" bgcolor="green" | Rryy |
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| width=22% align="center" bgcolor="red" | rrYy |
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| width=22% align="center" bgcolor="blue" | rryy |
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|} |
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The result in this cross is a 9:3:3:1 phenotypic ratio, as shown by the colors, where yellow represents a round yellow (both dominant genes) phenotype, green representing a round green phenotype, red representing a wrinkled yellow phenotype, and blue representing a wrinkled green phenotype (both recessive genes). |
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== See also == |
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* [[Monohybrid cross]] |
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[[Category:Classical genetics]] |
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[[sr:Дихибридно укрштање]] |
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[[sv:Dihybrid klyvning]] |
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[[tr:Dihibrit çaprazlama]] |
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Revision as of 19:29, 2 January 2009
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