Information Available from the F1 and F1 reciprocal progeny - Sex-Linkage 2

Females are the Heterogametic Sex - the ZZ - ZW system

The sex-chromosomes when females are the heterogametic sex are arbitrarily labeled as Z and W to distinguish them from the X and Y chromosomes.  This type of sex-determination is common in birds, fish, snakes, and butterflies.

Under the ZZ-ZW system females are the heterogametic sex. Females make eggs with a complete autosome set.  In addition, half of the eggs have an Z-chromosome and the other half of the eggs have a W- chromosome.  Males produce identical gametes (at the chromosome level of organization).  Each sperm has a complete set of autosomes and a Z-chromosome.

If the gene is on the Z-chromosome, then the females of the F1 and the reciprocal F1 generations will be different.  Females from the F1 and the reciprocal F1 generations will always have the phenotype of their homozygous fathers.  Consequently, the females of the F1 and the reciprocal F1 generations will have different phenotypes.  Females may or may not resemble their brothers depending on dominance.

The table below summaries the patterns that you expect to see the F1 and F1 reciprocal progeny assuming sex-linked inheritance (ZZ-ZW).  The F1 cross in every case is with an unknown, homozygous or hemizygous mutant with a homozygous or hemizygous wildtype individual.

Let A1 be the mutant allele and A2 be the wildtype allele on the Z-chromosome.  Let W represent the W-chromosome.  The F1 and reciprocal F1 crosses are shown below.

 

Dominance of Mutant Allele

 Sex-Linked ZZ-ZW
Recessive Phenotype
  1. The results of the reciprocal crosses are different.
  2.  F1 females have the phenotype of their fathers.
  3. F1 males are phenotypically wildtype

 
 Dominant Phenotype
  1. The results of the reciprocal crosses are different.
  2. F1 females have the phenotype of their fathers.
  3. F1 males are phenotypically mutant.
Incompletely Dominant Phenotype
  1. The results of the reciprocal crosses are different.
  2. F1 males have a phenotype that is intermediate to the parental phenotypes.
  3. F1 females have the phenotype of their fathers.
Overdominant Phenotype
  1. The results of the reciprocal crosses are different.
  2. F1 males have a phenotype that is more extreme than either of the parental phenotypes.
  3. F1 females have the phenotype of their fathers.
 
Codominant Phenotype
  1. The results of the reciprocal crosses are different.
  2. F1 males show both parental phenotypes, simultaneously.
  3. F1 females have the phenotype of their fathers.

Mendelian Genetics Index

F1 crosses
1 F1 cross -definition
2 Information Available from the F1 and F1 reciprocal progeny. 
4 F1  Autosomal Inheritance
4 F1  X - Linkage
5 F1  Z-Linkage
6 Summary Dominance Patterns for Autosomal & Sex-Linkage.
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