Question

Predict the \(F_{1}\) and \(F_{2}\) results of crossing a male fowl that is cock- feathered with a true-breeding hen-feathered female fowl. Recall that these traits are sex limited.

Short answer

Answer: If the male fowl is homozygous dominant (CC), then all offspring will be cock-feathered. If the male fowl is heterozygous (CH), then 50% of the offspring will be cock-feathered, and 50% of the offspring will be hen-feathered.

Step-by-step solution

Determine the genotypes of the parents

Use the abbreviations C (cock-feathered allele) and H (hen-feathered allele). Since the male is cock-feathered, he has either the CC or CH genotype. Since the female is true-breeding hen-feathered, she must have the HH genotype. Case 1: Male is CC (homozygous dominant) Father: CC Mother: HH Case 2: Male is CH (heterozygous) Father: CH Mother: HH

Set up Punnett squares for both cases

Now, let's set up two Punnett squares, one for each case. Case 1: | C | C | H| | | H| | | Case 2: | C | H | H| | | H| | |

Fill in the Punnett squares

Fill in the Punnett squares with the possible offspring genotypes resulting from the given parental genotypes. Case 1: | C | C | H| CH | CH | H| CH | CH | Case 2: | C | H | H| CH | HH | H| CH | HH |

Determine the phenotypes of offspring

Based on the genotypes in the Punnett squares, determine the phenotypes of the offspring for each case. Case 1: All offspring have the CH genotype, which means that all offspring will have cock-feathering. Case 2: Since cock-feathering is dominant, any offspring with the CH genotype (50% of the offspring) will be cock-feathered. The other 50% of the offspring, with the HH genotype, will display hen-feathering.

Predict the F1 and F2 results based on the two cases

Finally, let's predict the offspring for each case. If the male fowl is CC, then all offspring will be cock-feathered (F1). In the second case, if the male fowl is CH, then 50% of the offspring will be cock-feathered (F1), and 50% of the offspring will be hen-feathered (F2).

Key concepts

Punnett square

A Punnett square is a valuable tool used in genetics to predict the potential genotypes of offspring from a particular cross or breeding event. It's essentially a grid used to map out all possible combinations of parental alleles.

To create a Punnett square, list one parent's alleles across the top and the other's down the side. Each box within the grid represents a potential genotype for an offspring, formed by combining one allele from each parent.

This method helps visualize how dominant and recessive alleles can combine and thereby determine the likelihood of various genetic traits appearing in the offspring.

Genotype

In genetics, a genotype refers to the actual genetic makeup of an organism concerning a specific trait. It is represented by letters, where each allele is a variant of a gene. For example, the alleles for feather types in fowls might be represented as "C" for cock-feathered and "H" for hen-feathered.

A genotype can be homozygous, where both alleles are the same (CC or HH), or heterozygous, where the alleles are different (CH). This combination of alleles determines the organism’s phenotype, or its observable traits.

Phenotype

The phenotype of an organism is the set of its observable characteristics or traits, such as color, shape, and type of feathers in fowls. These traits are the result of interactions between its genotype and the environment.

In the provided exercise, the phenotypes for feathering types depend on the genetic makeup of the fowls. Cock-feathered and hen-feathered phenotypes result from different genotypes (e.g., CH and HH, respectively). The dominance of alleles plays a significant role in determining the phenotype.

Sex-limited traits

Sex-limited traits are those traits that are expressed in one sex but not the other, even though both sexes carry the genes for these traits. These traits are not found on the sex chromosomes, but their expression is influenced by the hormonal differences between males and females.

In fowls, cock-feathering is an example of a sex-limited trait, as it is typically expressed in males due to higher levels of certain hormones. Understanding these traits involves looking at how genotypes interact with sex-specific conditions to produce distinct phenotypes.