In chickens, feathered legs are produced by a dominant...

In chickens, feathered legs are produced by a dominant allele $F$. Another allele $f$ of the same gene produces featherless legs. The dominant allele $P$ of a gene at a different locus produces pea combs; a recessive allele $p$ of this gene causes single combs. A breeder makes the following crosses with birds $1,2,3,$ and $4 ;$ all parents have both feathered legs and pea combs: Cross Offspring $1 \times 2 \quad$ All feathered, pea comb $1 \times 3 \quad 3 / 4$ feathered; $1 / 4$ featherless, all pea comb $1 \times 4 \quad 9 / 16$ feathered, pea comb; $3 / 16$ featherless, pea comb $3 / 16$ feathered, single comb; $1 / 16$ featherless, single comb What are the genotypes of the four birds?

In chickens, feathered legs are produced by a dominant allele $F$. Another allele $f$ of the same gene produces featherless legs. The dominant allele $P$ of a gene at a different locus produces pea combs; a recessive allele $p$ of this gene causes single combs. A breeder makes the following crosses with birds $1,2,3,$ and $4 ;$ all parents have both feathered legs and pea combs:
Cross Offspring $1 \times 2 \quad$ All feathered, pea comb
$1 \times 3 \quad 3 / 4$ feathered; $1 / 4$ featherless, all pea comb
$1 \times 4 \quad 9 / 16$ feathered, pea comb; $3 / 16$ featherless, pea comb $3 / 16$ feathered, single comb; $1 / 16$ featherless, single comb
What are the genotypes of the four birds?

Key Concepts

Dihybrid Cross and Independent Assortment

A dihybrid cross involves individuals heterozygous for two traits and demonstrates the principle of independent assortment, where alleles for different traits segregate independently of one another. This cross typically yields a 9:3:3:1 ratio of phenotypic classes in the offspring when both traits exhibit complete dominance.

Genotype versus Phenotype

The genotype is the genetic make?up of an organism, while the phenotype is the observable expression of that genetic information. Understanding the difference is crucial, as the genotype may include carriers of recessive alleles that do not visibly affect the phenotype.

Punnett Square Analysis

Punnett squares are diagrammatic tools used to predict the probability of an offspring's genotype and phenotype from a cross between individuals. They help visually organize the segregation of alleles and determine the ratios of expected outcomes in genetic crosses.

Mendelian Inheritance

Mendelian inheritance involves the passing of traits from parents to offspring through discrete genes. These genes exist in different forms called alleles, and the traits follow predictable patterns of segregation and assortment according to Mendel’s laws.

Dominance and Recessiveness

In genetics, a dominant allele masks the phenotype of a recessive allele in a heterozygote. This concept explains why individuals with one dominant and one recessive allele display the trait associated with the dominant allele, while only individuals homozygous for the recessive allele exhibit the recessive phenotype.