Reciprocal Cross

Information about Reciprocal Cross

In genetics, a reciprocal cross is a breeding experiment designed to test the role of parental sex on a given inheritance pattern^[1]. 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 gene 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.

Reciprocal cross in practice

Given that the trait of interest is either autosomal or sex-linked 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^[2] 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 squares:

( X(wt)Y x X(mut)X(mut))

Table 1. Wild-type Male x Mutant Female
	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(mut)Y x X(wt)X(wt) )

Table 2. Mutant Male x Wild-type Female
	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^[3].

References

1. ^ [1]
2. ^ Doncaster L and Raynor GH (1906). Breeding experiments with Lepidoptera. Proceedings of the Zoological Society London, 1:125–133.
3. ^ [2]

External links

Simple Medelian Genetics in Drosophila

Genetics is the science of heredity and variation in living organisms.^[1]^[2] Knowledge of the inheritance of characteristics has been implicitly used since prehistoric times for improving crop plants and animals through selective breeding.
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A true breeding organism, sometimes also called a pure-bred, is an organism having certain biological traits which are passed on to all subsequent generations when bred with another true breeding organism for the same traits.
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The term DNA sequencing encompasses biochemical methods for determining the order of the nucleotide bases, adenine, guanine, cytosine, and thymine, in a DNA oligonucleotide.
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Molecular genetics is the field of biology which 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.
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An autosome is a non-sex chromosome. It is an ordinarily pairedIn the case of higher ploidy levels than the usual diploid, there will be the same number of an autosome as the ploidy level itself. For example, in a pentaploid, there will be five copies of each autosome.
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Sex linkage is the phenotypic expression of an allele that is related to the gender of the individual and is found on the sex chromosomes. This mode of inheritance is in contrast to the inheritance of traits on autosomal chromosomes, where both sexes have the same probability of
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dominance relationship refers to how the alleles for a locus interact to produce a phenotype.

There are three main kinds of dominance relationships:

Simple dominance or complete dominance (simple Mendelian inheritance) over a recessive trait

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D. melanogaster

Binomial name
Drosophila melanogaster
Meigen, 1830^[1]

Drosophila melanogaster (from the Greek for black-bellied dew-lover
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The Punnett square is a diagram designed by Reginald Punnett and used by biologists to determine the probability of an offspring having a particular genotype. It is made by comparing all the possible combinations of alleles from the mother with those from the father.
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For people named Carrier, see .

Carrier has several very different meanings:

in Science (physics, electronics, biology, mathematics, chemistry and other sciences)