The smooth feathers on the back of the neck in pigeons can be reversed by a mutation to produce a 'crested' appearance in which feathers form a distinctive spike at the back of the head. A pigeon breeder examined offspring produced by a single pair of non-crested birds and recorded the following: 22 non-crested and 7 crested. She then made a series of crosses using offspring from the first cross. When she crossed two of the crested birds, all 20 of the offspring were crested. When she crossed a non-crested bird with a crested bird, 7 offspring were non-crested and 6 were crested. For these three crosses, provide genotypes for parents and offspring that are consistent with these results.

Verified step by step guidance

1. Step 1: Determine the inheritance pattern. The data suggests that the crested trait is dominant because when two crested birds are crossed, all offspring are crested. This indicates that the crested phenotype (C) is dominant over the non-crested phenotype (c).
2. Step 2: Analyze the first cross (22 non-crested, 7 crested). Since both parents are non-crested and produce both crested and non-crested offspring, they must be heterozygous (Cc) to allow for the appearance of the dominant crested trait in their offspring.
3. Step 3: Assign genotypes to the offspring from the first cross. The ratio of non-crested to crested (approximately 3:1) suggests a Mendelian inheritance of a single gene. Therefore, the genotypes of the offspring are likely 1 CC (crested), 2 Cc (crested), and 1 cc (non-crested).
4. Step 4: Examine the second cross (two crested birds producing all crested offspring). Both parents are likely CC, as crossing two CC would result in 100% crested offspring (CC).
5. Step 5: Evaluate the third cross (7 non-crested, 6 crested from a non-crested and a crested parent). The non-crested parent must be cc, and the crested parent must be Cc, as this cross produces about a 1:1 ratio of non-crested to crested, consistent with a cross of cc x Cc.

Key Concepts

Genetics and Inheritance Patterns

Genetics is the study of heredity and the variation of inherited characteristics. In this context, understanding inheritance patterns, such as dominant and recessive traits, is crucial. The crested appearance in pigeons likely follows Mendelian inheritance, where one allele may dominate over another, influencing the phenotype of the offspring.

Phenotype and Genotype

The phenotype refers to the observable traits of an organism, such as feather appearance in pigeons, while the genotype is the genetic makeup that determines these traits. In this scenario, the non-crested and crested phenotypes suggest different genotypes, which can be represented using symbols to denote dominant and recessive alleles.

Punnett Squares and Genetic Crosses

Punnett squares are a tool used to predict the genotypes of offspring from genetic crosses. By analyzing the crosses described, one can set up Punnett squares to visualize the potential combinations of alleles from the parents, helping to determine the expected ratios of phenotypes in the offspring based on the genotypes of the parents.