Obtaining Parental Lines - Sex-Linked ZZ-ZW
Mutant Allele is Completely Dominant
How do Geneticists Get a New Parental Line?
| In the following discussion, genotypes in black (A2A2 or A2W ) are associated with the wildtype phenotype. Genotypes in blue (A1A1 & A1A2 or A1W) are associated with the dominant mutant phenotype. |
If the mutation is an Z-linked dominant it is actually easier to fix the allele than if the allele was autosomal because the genotype of the female is always known. Furthermore, the phenotype of the females for an Z-linked trait depends entirely on the genotype of the father.
If the father is homozygous A1A1, then all of his daughters will have the genotype A1W.
If the fathers heterozygous A1A2, then 1/2 all of his daughters will have the genotype A1W and the other 1/2 of his daughters will have the genotype A2W.
As previously discussed
it is
possible to obtain a generation of organisms for a dominant trait where the
males have the single dominant phenotype but two genotypes A1A1
and A1A2. The females have a mutant
and a wildtype phenotype corresponding to the genotypes A1W
and A2W.
The A2W wildtype females are discarded and mutant A1W females are mated to individual males who may be either A1A1 or A1A2.
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| The mutant males are individually mated to their sisters.
These mating are of two different types: Cross 1a: This cross produces only mutant males and mutant females. These can be intermated to produce a homozygous parental line. Cross 1b: If a wildtype daughter occurs, the father was A1A2 and all of the progeny can be discarded. The mutant progeny females might be kept for additional breeding (always preserve the allele) but the wildtype A2W females would be discarded. If only mutant daughters occur, there is a good
possibility that the father was A1A1 and all of the
sons are homozygous. The mutant males can then be mated to their mutant
sisters to establish a pure-breeding line. This is fairly reliable method
if sufficient females are produced (seven or more). |
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In species with very low fecundity it might be impossible to get a homozygous line.
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Related Tools |
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| Parental Lines | 1 |
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How to Obtain a Parental Line a) Autosomal Trait b) Sex-linked XX-XY c) sex-linked ZZ-ZW |
2 |
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How to Obtain a Parental Line for a Dominant Allele a) Autosomal Trait b) Sex-linked XX-XY c) sex-linked ZZ-ZW |
3 |
| How to Breed a Homozygous Line for more than one gene | 4 |
| F1 cross | 5 |