In experiments published in 1918 that sought to verify and expand the genetic linkage and recombination theory proposed by Morgan, Thomas Bregger studied potential genetic linkage in corn (Zea mays) for genes controlling kernel color (colored is dominant to colorless) and starch content (starchy is dominant to waxy). Bregger performed two crosses. In Cross 1, pure-breeding colored, starchy-kernel plants (C1 Wx/C1 Wx) were crossed to plants pure-breeding for colorless, waxy kernels (c1 wx/c1 wx). The F₁ of this cross were test-crossed to colorless, waxy plants. The test-cross progeny were as follows:

In Cross 2, plants pure-breeding for colored, waxy kernels (C1 wx/C1 wx) and colorless, starchy kernels (c1 Wx/c1 Wx) were mated, and their F₁ were test-crossed to colorless, waxy plants. The test-cross progeny were as follows:

Calculate the recombination frequency for each of the progeny groups.

Verified step by step guidance

1. Step 1: Understand the problem. The goal is to calculate the recombination frequency for each cross. Recombination frequency is calculated as the number of recombinant progeny divided by the total number of progeny, multiplied by 100 to express it as a percentage.
2. Step 2: Identify the parental and recombinant phenotypes. Parental phenotypes are the ones that match the original parental combinations, while recombinant phenotypes are the new combinations resulting from crossing over. For Cross 1, parental phenotypes are 'Colored, starchy' and 'Colorless, waxy,' while recombinant phenotypes are 'Colored, waxy' and 'Colorless, starchy.' Similarly, identify parental and recombinant phenotypes for Cross 2.
3. Step 3: Count the number of recombinant progeny. For Cross 1, add the numbers of 'Colored, waxy' and 'Colorless, starchy' progeny. For Cross 2, add the numbers of 'Colored, starchy' and 'Colorless, waxy' progeny.
4. Step 4: Calculate the total number of progeny for each cross. Add all the progeny numbers for Cross 1 and Cross 2 separately.
5. Step 5: Use the formula for recombination frequency: \( \text{Recombination Frequency} = \frac{\text{Number of Recombinant Progeny}}{\text{Total Number of Progeny}} \times 100 \). Perform this calculation for both Cross 1 and Cross 2 to determine the recombination frequencies.

Key Concepts

Genetic Linkage

Genetic linkage refers to the tendency of genes located close to each other on a chromosome to be inherited together during meiosis. This phenomenon occurs because linked genes are less likely to be separated by recombination events. Understanding genetic linkage is crucial for predicting the inheritance patterns of traits, as it affects the ratios of phenotypes observed in offspring.

Recombination Frequency

Recombination frequency is a measure of the likelihood that two genes will be separated during meiosis due to crossing over. It is calculated by dividing the number of recombinant offspring by the total number of offspring, then multiplying by 100 to express it as a percentage. This frequency helps in constructing genetic maps and understanding the distance between genes on a chromosome.

Test Cross

A test cross is a breeding experiment used to determine the genotype of an individual with a dominant phenotype. This is achieved by crossing the individual with a homozygous recessive individual. The phenotypic ratios of the offspring provide insights into whether the dominant individual is homozygous or heterozygous, which is essential for understanding inheritance patterns in genetic studies.