Dihybrid cross is a cross between two individuals with two observed traits that are controlled by two distinct genes. 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 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 was an Austrian-Czech monk who bred peas plants in his monastery garden and compared 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 the phenotypic ratio (9:3:3:1) seen in dihybrid cross for a heterozygous cross.

thumb|This is a dihybrid cross of two heterozygous parents. The traits observed in this cross are the same traits that Mendel was observing for his experiments. This cross results in the expected phenotypic ratio of 9:3:3:1.

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, and the recessive traits of the same characteristic is lowercase.

  • In the following case the example of pea plant seed is chosen. The two characteristics being compared are
  1. Shape: round or wrinkled (Round (R) is dominant)
  2. 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.

{| class="wikitable" style="text-align:center; width:50%"

|-

!

! RY !! Ry !! rY !! ry

|-

! RY

| RRYY || RRYy || RrYY || RrYy

|-

! Ry

| RRYy || RRyy || RrYy || Rryy

|-

! rY

| RrYY || RrYy || rrYY || rrYy

|-

! ry

| RrYy || Rryy || rrYy || rryy

|}

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See also

  • Gregor Mendel
  • William Bateson
  • Mendelian inheritance
  • Law of dominance
  • Law of segregation
  • Law of independent assortment
  • Monohybrid cross

References

  • "Dihybrid cross" - The Mosby Medical Encyclopedia
  • "Dihybrid Cross - A Genetics Definition" - About:Biology