Reciprocal cross
Encyclopedia
In genetics
, a reciprocal cross is a breeding experiment designed to test the role of parental sex on a given inheritance pattern. All parent organisms must be true breeding to properly carry out such an experiment. In one cross, a male expressing the trait of interest will be crossed with a female not expressing the trait. In the other, a female expressing the trait of interest will be crossed with a male not expressing the trait.
For example, suppose a biologist wished to identify whether a hypothetical allele Z, a variant of some gene A, is on the male or female sex chromosome. He might first cross a Z-trait female with an A-trait male and observe the offspring. Next, he would cross an A-trait female with a Z-trait male and observe the offspring. Via principles of dominant and recessive alleles, he could then (perhaps after cross-breeding the offspring as well) make an inference as to which sex chromosome contains the gene Z, if either in fact did.
Such types of experiments are unlikely to actually be carried out in the contemporary era of DNA sequencing
and molecular genetics
.
and follows by either complete dominance or incomplete dominance, a reciprocal cross following two generations will determine the mode of inheritance of the trait.
White-eye mutation in Drosophila melanogaster
Sex linkage
was first reported by Doncaster and Raynor in 1906 who studied the white-eye mutation in Drosophila melanogaster
. They found that a white-eyed male crossed with a red-eyed female produced only red-eyed offspring. However, when they crossed a red-eyed male with a white-eyed female, the male offspring had white eyes while the female offspring had red eyes. The reason was that the white eye allele is sex-linked (more specifically, on the X chromosome) and recessive.
The analysis can be more easily shown with Punnett square
s:
As shown in Table 1, the male offspring are white-eyed and the female offspring are red-eyed. The female offspring are carrying the mutant white-eye allele X(mut), but do not express it phenotypically because it is recessive. Although the males carry only one mutant allele like the females, the X-chromosome takes precedence over the Y and the recessive phenotype is shown.
As shown in Table 2, all offspring are Red-eyed. The males are free of the mutation. The females however, are carriers
.
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
, a reciprocal cross is a breeding experiment designed to test the role of parental sex on a given inheritance pattern. All parent organisms must be true breeding to properly carry out such an experiment. In one cross, a male expressing the trait of interest will be crossed with a female not expressing the trait. In the other, a female expressing the trait of interest will be crossed with a male not expressing the trait.
For example, suppose a biologist wished to identify whether a hypothetical allele Z, a variant of some gene A, is on the male or female sex chromosome. He might first cross a Z-trait female with an A-trait male and observe the offspring. Next, he would cross an A-trait female with a Z-trait male and observe the offspring. Via principles of dominant and recessive alleles, he could then (perhaps after cross-breeding the offspring as well) make an inference as to which sex chromosome contains the gene Z, if either in fact did.
Such types of experiments are unlikely to actually be carried out in the contemporary era of DNA sequencing
DNA sequencing
DNA sequencing includes several methods and technologies that are used for determining the order of the nucleotide bases—adenine, guanine, cytosine, and thymine—in a molecule of DNA....
and molecular genetics
Molecular genetics
Molecular genetics is the field of biology and genetics that studies the structure and function of genes at a molecular level. The field studies how the genes are transferred from generation to generation. Molecular genetics employs the methods of genetics and molecular biology...
.
Reciprocal cross in practice
Given that the trait of interest is either autosomal or sex-linkedSex linkage
Sex linkage is the phenotypic expression of an allele related to the chromosomal sex of the individual. This mode of inheritance is in contrast to the inheritance of traits on autosomal chromosomes, where both sexes have the same probability of inheritance...
and follows by either complete dominance or incomplete dominance, a reciprocal cross following two generations will determine the mode of inheritance of the trait.
White-eye mutation in Drosophila melanogasterDrosophila melanogasterDrosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...
Sex linkageSex linkage
Sex linkage is the phenotypic expression of an allele related to the chromosomal sex of the individual. This mode of inheritance is in contrast to the inheritance of traits on autosomal chromosomes, where both sexes have the same probability of inheritance...
was first reported by Doncaster and Raynor in 1906 who studied the white-eye mutation in Drosophila melanogaster
Drosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...
. They found that a white-eyed male crossed with a red-eyed female produced only red-eyed offspring. However, when they crossed a red-eyed male with a white-eyed female, the male offspring had white eyes while the female offspring had red eyes. The reason was that the white eye allele is sex-linked (more specifically, on the X chromosome) and recessive.
The analysis can be more easily shown with Punnett square
Punnett square
The Punnett square is a diagram that is used to predict an outcome of a particular cross or breeding experiment. It is named after Reginald C. Punnett, who devised the approach, and is used by biologists to determine the probability of an offspring's having a particular genotype...
s:
| X (mut) | X (mut) | |
|---|---|---|
| X (wt) | X (mut) X (wt) Red eye Female |
X (mut) X (wt) Red eye Female |
| Y | X (mut) Y White eye Male |
X (mut) Y White eye Male |
| X (wt) | X (wt) | |
|---|---|---|
| X (mut) | X (mut) X (wt) Red eye Female |
X (mut) X (wt) Red eye Female |
| Y | X (wt) Y Red eye Male |
X (wt) Y Red eye Male |
As shown in Table 1, the male offspring are white-eyed and the female offspring are red-eyed. The female offspring are carrying the mutant white-eye allele X(mut), but do not express it phenotypically because it is recessive. Although the males carry only one mutant allele like the females, the X-chromosome takes precedence over the Y and the recessive phenotype is shown.
As shown in Table 2, all offspring are Red-eyed. The males are free of the mutation. The females however, are carriers
Genetic carrier
A genetic carrier , is a person or other organism that has inherited a genetic trait or mutation, but who does not display that trait or show symptoms of the disease. They are, however, able to pass the gene onto their offspring, who may then express the gene...
.