Recombination frequency is a measure of the likelihood that a crossover will occur between two genes during meiosis, leading to the exchange of genetic material between homologous chromosomes. It is expressed as a percentage and is used to estimate the physical distance between genes on a chromosome. A recombination frequency of 1% corresponds to a genetic distance of 1 map unit (centimorgan, cM).

Example 1

Scenario: Suppose you are studying two linked genes, A and B, in fruit flies. 

You cross a fly with genotype AABB with a fly with genotype aabb. The resulting F1 generation is heterozygous AaBb. These F1 flies are then test crossed (crossed with aabb flies), and the following offspring are observed:

• • AB: 400

  • ab: 390

  • Ab: 50

  • aB: 60

Total Offspring: 400 + 390 + 50 + 60 = 900

"Now you need to calculate the recombination frequency to determine the likelihood that a crossover will occur between two genes?

Answer: There are different steps to Calculate Recombination Frequency

Step 1: Identify Parental and Recombinant Types:

1. • Parental types are the offspring that inherit the parental combinations of alleles and these are with maximum in number.

   • Recombinant types are the offspring that inherit new combinations of alleles due to crossover events and are minimum in number.

Step 2: Count the Number of Each Type:

1. • Determine the number of offspring displaying the parental phenotypes (400 + 390=790).

   • Determine the number of offspring displaying the recombinant phenotypes (50 + 60=110)

Step 3: Calculate the Recombination Frequency using the Formula:

Recombination Frequency (RF)= Total Number of Recombinant/Total Number of Individuals*100

RF= 50 + 60/900*100

RF= 110/900*100

RF= 0.12222*100

RF=12.22%

Thus, the recombination frequency between genes A and B is 12.22%, means that 12.22% chance that a crossover will separate these genes during meiosis 

Interpretation

A recombination frequency of 12.22% suggests that there is a 12.22% chance that a crossover event will occur between genes A and B during meiosis. This frequency helps in determining the genetic distance and constructing genetic maps to understand the layout of genes on chromosomes.

Example 2

Calculating Recombination Frequency

Scenario: You are studying two linked genes, D (dominant for dark eyes) and R (dominant for red wings), in a species of beetle. You want to determine the recombination frequency between these two genes to understand how closely they are linked on the chromosome.

1. Crossing the Beetles:

   • You cross a homozygous beetle with dark eyes and red wings (DDRR) with a homozygous beetle with light eyes and white wings (ddrr).

   • The F1 offspring are all heterozygous for both traits (DdRr).

2. Testcross:

   • You perform a testcross by mating the F1 heterozygous beetles (DdRr) with homozygous recessive beetles (ddrr).

3. Offspring Phenotypes:

   • You obtain the following phenotypes among the 800 offspring:

     • Dark eyes and red wings (Parental): 340

     • Light eyes and white wings (Parental): 330

     • Dark eyes and white wings (Recombinant): 70

     • Light eyes and red wings (Recombinant): 60

4. Calculate Recombination Frequency:

   • Identify parental and recombinant offspring.

   • Use the formula to find the recombination frequency.

Answer: 

Steps:

Step 1: Identify Parental and Recombinant Types:

1. • Parental Types: Dark eyes and red wings (DDRR), Light eyes and white wings (ddrr).

   • Recombinant Types: Dark eyes and white wings (D_rr), Light eyes and red wings (d_RR).

Step 2: Count the Number of Each Type:

1. • Parental Offspring:

     • Dark eyes and red wings: 340

     • Light eyes and white wings: 330

     • Total parental: 340+330=670 

   • Recombinant Offspring:

     • Dark eyes and white wings: 70

     • Light eyes and red wings: 60

     • Total recombinant: 70+60=130

Step 3: Total Number of Offspring:
Total Offspring=670 (Parental)+130 (Recombinant)=800

Step 4: Calculate Recombination Frequency: Recombination Frequency (RF)= Total Number of Recombinant/Total Number of Individuals*100

RF= 70+60/800*100

= 130/800*100

= 0.1625*100

RF =16.25%

The recombination frequency between the genes for dark eyes (D) and red wings (R) is 16.25%.

Interpretation: A recombination frequency of 16.25% indicates that there is a 16.25% chance that a crossover event will occur between the D and R genes during meiosis. This suggests that these genes are relatively close to each other on the chromosome, but not so close as to be completely linked.