If there is crossing over between two gene loci A and C occurs in 20% of the tetrads and between C and B in 10% of an individual of genotype ACB/acb, what would be the percentage of gametes of double cross over types (AcB/aCb) ?
To determine the percentage of gametes of double crossover types (AcB/aCb), we need to understand the concept of crossing over and how it affects gamete formation.
Crossing over is a genetic phenomenon that occurs during meiosis, specifically in the process of chromosome exchange between homologous chromosomes. It leads to the shuffling of genetic material between chromosome pairs, creating new combinations of alleles.
In your question, we are given the crossing over frequencies between two gene loci: A and C (20%) and C and B (10%). Given that the genotype of the individual is ACB/acb, we can break it down into two gene pairs: A and C and C and B.
To calculate the percentage of gametes with double crossover types (AcB/aCb), you need to consider the crossing over between A and C and C and B independently, and then multiply those individual probabilities together.
Let's calculate it step by step:
1. Calculate the probability of crossover between A and C (20%):
- Since the crossover frequency is 20%, it means that in 20% of the tetrads (group of four chromatids), crossing over occurs between A and C.
- This implies that there is a 20% chance of recombination between these two gene loci.
- Therefore, the probability of a single crossover between A and C is 0.20.
2. Calculate the probability of crossover between C and B (10%):
- Similarly, since the crossover frequency is 10%, there is a 10% chance of recombination between C and B.
- Therefore, the probability of a single crossover between C and B is 0.10.
3. Multiply the probabilities of single crossovers together to get the probability of a double crossover between A, C, and B:
- P(AcB/aCb) = P(A-C) * P(C-B)
- P(AcB/aCb) = 0.20 * 0.10
- P(AcB/aCb) = 0.02 or 2%
Hence, the percentage of gametes with double crossover types (AcB/aCb) is 2%.