6. Cross of Andalusian Fowls
In the given scenario, black (B) and white (b) are the alleles for feather color in Andalusian fowls. The black individuals are homozygous (BB), and the white individuals are homozygous (bb). The cross is as follows:
Cross:
- Parent 1: Homozygous Black (BB)
- Parent 2: Homozygous White (bb)
When these two are crossed, all offspring (F1 generation) will have the genotype Bb (heterozygous) and will express the bluish-grey phenotype.
Punnett Square:
B B
--------------
b | Bb | Bb |
--------------
b | Bb | Bb |
--------------
Genotypic Ratio:
- Bb : 100% (4 Bb)
Phenotypic Ratio:
- Bluish-grey : 100% (4 bluish-grey)
7. Punnett Square for Black-and-White Speckled Chickens
In this scenario, we are dealing with two black-and-white speckled chickens (BW), where B represents the black allele and W represents the white allele. When two BW individuals are bred, we can set up a Punnett square to determine the genotypes and phenotypes of the offspring.
Punnett Square:
B W
----------------
B | BB | BW |
----------------
W | BW | WW |
----------------
Offspring Genotypes:
- BB: 1
- BW: 2
- WW: 1
Genotypic Ratio:
- BB : 1
- BW : 2
- WW : 1
- Ratio: 1 : 2 : 1
Offspring Phenotypes:
- Black-feathered (BB): 1
- Black-and-white speckled (BW): 2
- White-feathered (WW): 1
Phenotypic Ratio:
- Black : 1
- Speckled : 2
- White : 1
- Ratio: 1 : 2 : 1
Inheritance Pattern
The inheritance pattern displayed in this chicken breeding example is known as codominance. In codominance, both alleles in a heterozygous individual contribute to the phenotype, resulting in a distinct expression that is not a mix or blend of the two traits. In this case, the presence of both black (B) and white (W) alleles results in speckled feathers (BW) in the heterozygous condition (BW). Neither allele is recessive, and both traits are fully expressed in the phenotype.