genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar wor ...

, 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 Purebreds are "cultivated varieties" of an animal species achieved through the process of selective breeding. When the lineage of a purebred animal is recorded, that animal is said to be "pedigreed". Purebreds breed true-to-type which means the p ...

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. It is the cross that could be made either way or independent of the sex of the parents. 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. They might first cross a Z-trait female with an A-trait male and observe the offspring. Next, they would cross an A-trait female with a Z-trait male and observe the offspring. Via principles of dominant and recessive alleles, they 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.

Reciprocal cross in practice

Given that the trait of interest is either

autosomal An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosome, allosomal (sex chromosome) pairs, which may have different structures. The DNA in au ...

sex-linked Sex linked describes the sex-specific patterns of inheritance and presentation when a gene mutation (allele) is present on a sex chromosome (allosome) rather than a non-sex chromosome ( autosome). In humans, these are termed X-linked recessive, ...

and follows by either

complete dominance In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...

incomplete dominance In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and ...

, a reciprocal cross following two generations will determine the mode of inheritance of the trait.

White-eye mutation in ''Drosophila melanogaster''

Sex linkage Sex linked describes the sex-specific patterns of inheritance and presentation when a gene mutation (allele) is present on a sex chromosome (allosome) rather than a non-sex chromosome (autosome). In humans, these are termed X-linked recessive, ...

was first reported by Doncaster and Raynor in 1906 who studied the inheritance of a colour mutation in a moth, ''Abraxas grossulariata''.

Thomas Hunt Morgan Thomas Hunt Morgan (September 25, 1866 – December 4, 1945) was an American evolutionary biologist, geneticist, embryologist, and science author who won the Nobel Prize in Physiology or Medicine in 1933 for discoveries elucidating the role tha ...

later showed that a new white-eye mutation in

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly" or "pomace fly". Starting with Ch ...

was also sex-linked. He 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 squares: {, class="wikitable" , + Table 2. Mutant Male x Wild-type Female ( X(mut)Y x X(wt)X(wt) ) ! ! 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.Fruit Fly Genetics
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References

External links

Classical genetics