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Dihybrid cross is a cross between two individuals with two observed traits that are controlled by two distinct genes. If one of the parents is homozygous dominant for both genes and the other parent is homozygous recessive for both genes, then the offspring will be uniformly heterozygous for both genes and will display the dominant phenotype for both traits. Self-pollination or crossing of these individuals will result in predictable ratios of both genotype and phenotype in the F2 generation. The expected phenotypic ratio of crossing heterozygous parents would be 9:3:3:1^[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.

Article body

Mendelian History

Gregor Mendal was an Austrian monk who bred peas plants in his monastery garden and compared the offspring to figure out inheritance of traits^[1]. He first started looking at individual traits, but began to look at two distinct traits in the same plant. His first experiment looking at two distinct traits was found by looking at 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^[1]. From these experiments, he determined the phenotypic ratio (9:3:3:1) seen in dihybrid cross for a heterozygous cross^[2].

Through these experiments, he was able to determine the basic law of independent assortment. This law states that traits controlled by different genes are going to be inherited independently of each other^[2]. Mendel was able to figure this law out because with his crosses he was able to get all four possible phenotypes.

Expected genotype and phenotype ratios[edit]

The phenotypic ratio of the F2 offspring of the cross is 9:3:3:1, where 9/16 of the F2 individuals possess the dominant phenotype for both traits, and 1/16 are recessive for both traits^[1]. This phenotypic ratio only applies to Angiosperms or similar sexually reproducing organisms.

According to Mendel's statement, the relationship between alleles of both these loci is complete dominance, meaning if one dominant allele is inherited, the resulting phenotype for that gene will be the dominant phenotype^[3]. In the example pictured to the right, the cross of RRYY/rryy parents results in F₁ offspring that are heterozygous for both R and Y (RrYy). The following F2 generation results in the expected 9:3:3:1 phenotypic ratio.

Another example is listed in the table below and illustrates the process of dihybrid crosses between pea plants with multiple traits and their phenotypic ratio patterns. Dihybrid crosses are easily visualized using a Punnett square of dimensions 16. In these squares, the dominant traits are uppercase, and the recessive traits of the same characteristic are lowercase.

In the following case the example of pea plant seed is chosen. The two characteristics being compared are

Shape: round or wrinkled
colour: yellow or green

R (roundness) is dominant and Y (yellow colour of seed) is dominant. This implies that Rr will be a round seed and Yy will be a yellow seed. Only rr will be wrinkled seed and yy will be green seed. This exhibits the idea of complete dominance.

F₁Gametes F₁ Gametes	RY	Ry	rY	ry
RY	RRYY	RRYy	RrYY	RrYy
Ry	RRYy	RRyy	RrYy	Rryy
rY	RrYY	RrYy	rrYY	rrYy
ry	RrYy	Rryy	rrYy	rryy

The rules of meiosis, as they apply to the dihybrid, are stated in Mendel's first and second law, which are also known as the Law of Segregation and the Law of Independent Assortment, respectively^[2].

For genes on separate chromosomes, each allele pair showed independent segregation. If the F1 generation produces four identical offspring, the F2 generation, which occurs by crossing the members of the F1 generation, shows a phenotypic (appearance) ratio of 9:3:3:1, where:

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 Dihybrid phenotypic ratio= 9:3:3:1
The genotypic ratio are: RRYY 1: RRYy 2: RRyy 1: RrYY 2: RrYy 4: Rryy 2: rrYY 1: rrYy 2: rryy 1.

References

^ ^a ^b ^c ^d Ahluwalia, Karvita B. (2009). Genetics (2nd ed ed.). New Delhi: New Age International. ISBN 978-81-224-2880-3. OCLC 430838253. {{cite book}}: |edition= has extra text (help)
^ ^a ^b ^c Klug, William S. (2015). Concepts of genetics. Michael R. Cummings, Charlotte A. Spencer, Michael Angelo Palladino (Eleventh edition ed.). Boston. ISBN 978-0-321-94891-5. OCLC 880404074. {{cite book}}: |edition= has extra text (help)CS1 maint: location missing publisher (link)
^ "The Dihybrid Cross" - Open Door Archived February 7, 2010, at the Wayback Machine

[:0-1] Ahluwalia, Karvita B. (2009). Genetics (2nd ed ed.). New Delhi: New Age International. ISBN 978-81-224-2880-3. OCLC 430838253. {{cite book}}: |edition= has extra text (help)

[:1-2] Klug, William S. (2015). Concepts of genetics. Michael R. Cummings, Charlotte A. Spencer, Michael Angelo Palladino (Eleventh edition ed.). Boston. ISBN 978-0-321-94891-5. OCLC 880404074. {{cite book}}: |edition= has extra text (help)CS1 maint: location missing publisher (link)

[3] "The Dihybrid Cross" - Open Door Archived February 7, 2010, at the Wayback Machine

[1]

[2]

[3]

@@ Line 4: / Line 4: @@
 === Lead ===
-'''Dihybrid cross''' is a cross between two individuals with two observed [[Phenotypic trait|traits]] that are controlled by two distinct [[Gene|genes]]. If one of the parents is [[homozygous]] dominant for both genes and the other parent is homozygous recessive for both genes, then the offspring will be uniformly [[heterozygous]] for both genes and will display the [[Dominance (genetics)|dominant]] phenotype for both traits. Self-pollination or crossing of these individuals will result in predictable ratios of both [[genotype]] and [[phenotype]] in the [[F1 hybrid|F2]] generation. 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 [[Genetic linkage|linked]] or that one or both traits has a [[Non-Mendelian inheritance|non-Mendelian]] mode of inheritance.
+'''Dihybrid cross''' is a cross between two individuals with two observed [[Phenotypic trait|traits]] that are controlled by two distinct [[Gene|genes]]. If one of the parents is [[homozygous]] dominant for both genes and the other parent is homozygous recessive for both genes, then the offspring will be uniformly [[heterozygous]] for both genes and will display the [[Dominance (genetics)|dominant]] phenotype for both traits. Self-pollination or crossing of these individuals will result in predictable ratios of both [[genotype]] and [[phenotype]] in the [[F1 hybrid|F2]] generation. The expected phenotypic ratio of crossing heterozygous parents would be 9:3:3:1<ref name=":0" />. Deviations from these expected ratios may indicate that the two traits are [[Genetic linkage|linked]] or that one or both traits has a [[Non-Mendelian inheritance|non-Mendelian]] mode of inheritance.
 === Article body ===
 == Mendelian History ==
-Gregor Mendal was an Austrian monk who bred peas plants in his monastery garden and compared the offspring to figure out inheritance of traits<ref name=":0">{{Cite book |last=Ahluwalia |first=Karvita B. |url=https://www.worldcat.org/oclc/430838253 |title=Genetics |date=2009 |publisher=New Age International |isbn=978-81-224-2880-3 |edition=2nd ed |location=New Delhi |oclc=430838253}}</ref>. He first started looking at individual traits, but began to look at two distinct traits in the same plant. His first experiment looking at two distinct traits was found by looking at 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<ref name=":0" />. From these experiments, he determined the phenotypic ratio (9:3:3:1) seen in dihybrid cross for a heterozygous cross<ref>{{Cite book |last=Klug |first=William S. |url=https://www.worldcat.org/oclc/880404074 |title=Concepts of genetics |date=2015 |others=Michael R. Cummings, Charlotte A. Spencer, Michael Angelo Palladino |isbn=978-0-321-94891-5 |edition=Eleventh edition |location=Boston |oclc=880404074}}</ref>.
+Gregor Mendal was an Austrian monk who bred peas plants in his monastery garden and compared the offspring to figure out inheritance of traits<ref name=":0">{{Cite book |last=Ahluwalia |first=Karvita B. |url=https://www.worldcat.org/oclc/430838253 |title=Genetics |date=2009 |publisher=New Age International |isbn=978-81-224-2880-3 |edition=2nd ed |location=New Delhi |oclc=430838253}}</ref>. He first started looking at individual traits, but began to look at two distinct traits in the same plant. His first experiment looking at two distinct traits was found by looking at 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<ref name=":0" />. From these experiments, he determined the phenotypic ratio (9:3:3:1) seen in dihybrid cross for a heterozygous cross<ref name=":1">{{Cite book |last=Klug |first=William S. |url=https://www.worldcat.org/oclc/880404074 |title=Concepts of genetics |date=2015 |others=Michael R. Cummings, Charlotte A. Spencer, Michael Angelo Palladino |isbn=978-0-321-94891-5 |edition=Eleventh edition |location=Boston |oclc=880404074}}</ref>.
-Through these experiments, he was able to determine the basic law of independent assortment. This law states that traits controlled by different genes are going to be inherited independently of each other. Mendel was able to figure this law out because with his crosses he was able to get all four possible phenotypes.
+Through these experiments, he was able to determine the basic law of independent assortment. This law states that traits controlled by different genes are going to be inherited independently of each other<ref name=":1" />. Mendel was able to figure this law out because with his crosses he was able to get all four possible phenotypes.
 == Expected genotype and phenotype ratios[edit] ==
-The phenotypic ratio of the F2 offspring of the cross is 9:3:3:1, where 9/16 of the F2 individuals possess the dominant phenotype for both traits, and 1/16 are recessive for both traits. This phenotypic ratio only applies to [[Flowering plant|Angiosperms]] or similar sexually reproducing organisms.
+The phenotypic ratio of the F2 offspring of the cross is 9:3:3:1, where 9/16 of the F2 individuals possess the dominant phenotype for both traits, and 1/16 are recessive for both traits<ref name=":0" />. This phenotypic ratio only applies to [[Flowering plant|Angiosperms]] or similar sexually reproducing organisms.
-According to Mendel's statement, the relationship between [[Allele|alleles]] of both these loci is complete dominance, meaning if one dominant allele is inherited, the resulting phenotype for that gene will be the dominant phenotype. In the example pictured to the right, the cross of RRYY/rryy parents results in F<sub>1</sub> offspring that are [[heterozygous]] for both R and Y (RrYy). The following F2 generation results in the expected 9:3:3:1 phenotypic ratio.
+According to Mendel's statement, the relationship between [[Allele|alleles]] of both these loci is complete dominance, meaning if one dominant allele is inherited, the resulting phenotype for that gene will be the dominant phenotype<ref>"The Dihybrid Cross" - Open Door Archived February 7, 2010, at the [[Wayback Machine]]</ref>. In the example pictured to the right, the cross of RRYY/rryy parents results in F<sub>1</sub> offspring that are [[heterozygous]] for both R and Y (RrYy). The following F2 generation results in the expected 9:3:3:1 phenotypic ratio.
 Another example is listed in the table below and illustrates the process of dihybrid crosses between pea plants with multiple traits and their phenotypic ratio patterns. Dihybrid crosses are easily visualized using a [[Punnett square]] of dimensions 16. In these squares, the [[Dominance (genetics)|dominant traits]] are [[UPPERCASE|uppercase]], and the [[Dominance (genetics)|recessive traits]] of the same characteristic are [[lowercase]].
@@ Line 60: / Line 60: @@
 |rryy
 |}
-The rules of [[meiosis]], as they apply to the dihybrid, are stated in [[Law of Segregation|Mendel's first]] and [[Law of Independent Assortment|second law]], which are also known as the [[Law of Segregation]] and the [[Law of Independent Assortment]], respectively.
+The rules of [[meiosis]], as they apply to the dihybrid, are stated in [[Law of Segregation|Mendel's first]] and [[Law of Independent Assortment|second law]], which are also known as the [[Law of Segregation]] and the [[Law of Independent Assortment]], respectively<ref name=":1" />.
 For genes on separate [[Chromosome|chromosomes]], each [[allele]] pair showed independent segregation. If the F1 generation produces four identical offspring, the F2 generation, which occurs by crossing the members of the F1 generation, shows a [[Phenotype|phenotypic]] (appearance) ratio of 9:3:3:1, where: