Dihybrid cross is a cross between two individuals with two observed traits that are controlled by two distinct

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

s. The idea of a dihybrid cross came from Gregor Mendel when he observed pea plants that were either yellow or green and either round or wrinkled. Crossing of two heterozygous individuals will result in predictable ratios for both genotype and

phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological pr ...

in the offspring. The expected phenotypic ratio of crossing heterozygous parents would be 9:3:3:1. Deviations from these expected ratios may indicate that the two traits are linked or that one or both traits has a non-Mendelian mode of inheritance.

Mendelian History

Gregor Mendel Gregor Johann Mendel, OSA (; cs, Řehoř Jan Mendel; 20 July 1822 – 6 January 1884) was a biologist, meteorologist, mathematician, Augustinian friar and abbot of St. Thomas' Abbey in Brünn (''Brno''), Margraviate of Moravia. Mendel was ...

was an Austrian monk who bred peas plants in his monastery garden and compared the offspring to figure out inheritance of traits form 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 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 Mendelian inheritance (also known as Mendelism) is a type of biological inheritance following the principles originally proposed by Gregor Mendel in 1865 and 1866, re-discovered in 1900 by Hugo de Vries and Carl Correns, and later populariz ...

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 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.

Expected genotype and phenotype ratios

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 the dominant phenotype for the other trait, and 1/16 are recessive for both traits. Valid only for

Angiosperms Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants ...

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: * the 9 represents the proportion of individuals displaying both dominant traits: 1 x RRYY + 2 x RRYy + 2 x RrYY + 4 x RrYy * the first 3 represents the individuals displaying the first dominant trait and the second recessive trait: 1 x RRyy + 2 x Rryy * the second 3 represents those displaying the first recessive trait and second dominant trait: 1 x rrYY + 2 x rrYy * the 1 represents the homozygous, displaying both recessive traits: 1 x rryy * The genotypic ratio are: RRYY 1: RRYy 2: RRyy 1: RrYY 2: RrYy 4: Rryy 2: rrYY 1: rrYy 2: rryy 1 In the example pictured to the right, RRYY/rryy parents result in F₁ offspring that are

heterozygous Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...

for both R and Y (RrYy)."The Dihybrid Cross" - Open Door
Figure 12 03 02

Another example is listed in the table below and illustrates the process of a dihybrid cross between pea plants with multiple traits and their phenotypic ratio patterns. Dihybrid crosses are easily visualized using a 4 x 4 Punnett square. In these squares, the dominant traits are

uppercase Letter case is the distinction between the letters that are in larger uppercase or capitals (or more formally ''majuscule'') and smaller lowercase (or more formally ''minuscule'') in the written representation of certain languages. The writing ...

, and the recessive traits of the same characteristic is

lowercase Letter case is the distinction between the letters that are in larger uppercase or capitals (or more formally ''majuscule'') and smaller lowercase (or more formally ''minuscule'') in the written representation of certain languages. The writing ...

. * In the following case the example of

pea plant The pea is most commonly the small spherical seed or the seed-pod of the flowering plant species ''Pisum sativum''. Each pod contains several peas, which can be green or yellow. Botanically, pea pods are fruit, since they contain seeds and d ...

seed is chosen. The two characteristics being compared are # Shape: round or wrinkled (Round (R) is dominant) # Color: yellow or green (Yellow (Y) is dominant) * This implies that Rr will be a round seed and Yy will be a yellow seed. Only rr will be a wrinkled seed and yy will be a green seed. * Pisum-dihybrid

References

External links

"Dihybrid cross" - The Mosby Medical Encyclopedia

{{DEFAULTSORT:Dihybrid Cross Classical genetics

Mendelian History

Expected genotype and phenotype ratios

See also

References

External links