2. Assume you are performing a cross between a plant that is heterozygous for the dominant traits red flowers and wrinkled seeds, with a plant that is homozygous for the recessive traits white flowers and smooth seeds. Assume the alleles are R for red flowers, r for white flowers, W for wrinkled seeds, and w for smooth seeds. The offspring of this cross show the following phenotypes:
43 red flowers and wrinkled seeds
7 red flowers and smooth seeds
9 white flowers and wrinkled seeds
41 white flowers and smooth seeds
What are the traits of the recombinant offspring in terms of flower color and seed shape? Explain how you know that these offspring are recombinant. What alleles would you expect to see in the individual chromosomes of each parent before and after crossing-over takes place? What is the recombination frequency? What is the distance between the genes in map units?
I'm very confused on how I'm suposed to figure out how to answer it.
To determine the traits of the recombinant offspring, we need to understand the principles of Mendelian genetics and the concept of recombination. Let's break down the process step by step:
1. Determine the genotypes of each parent:
- Parent 1: Heterozygous for dominant traits (RrWw)
- Parent 2: Homozygous for recessive traits (rrww)
2. Determine the possible gametes produced by each parent:
- Parent 1: Can produce four types of gametes (RW, Rw, rW, rw)
- Parent 2: Can produce two types of gametes (rw)
3. Combine the gametes in a Punnett square:
| R | r |
____________________
W | RW | rW |
____________________
w | Rw | rw |
The Punnett square shows all possible combinations of gametes from each parent.
4. Analyze the phenotypes of the offspring:
- 43 red flowers and wrinkled seeds (RW)
- 7 red flowers and smooth seeds (Rw)
- 9 white flowers and wrinkled seeds (rW)
- 41 white flowers and smooth seeds (rw)
5. Determine the recombinant offspring:
Recombinant offspring occur when there is a combination of traits that is different from the parents. In this case, the recombinant offspring are those with different phenotypes from either parent.
In this case, the recombinant offspring are the 7 individuals with red flowers and smooth seeds (Rw).
6. Determine the alleles on the individual chromosomes of each parent before and after crossing-over:
Before crossing-over:
- Parent 1: Rr and Ww
- Parent 2: rr and ww
After crossing-over:
Crossing-over is a process in meiosis where genetic material is exchanged between homologous chromosomes. As a result, the allele combinations on individual chromosomes may change. In this case, the alleles on individual chromosomes would be:
- Parent 1: Rr and Ww (unchanged)
- Parent 2: rr and ww (unchanged)
7. Calculate the recombination frequency:
Recombination frequency is a measure of the likelihood of recombination occurring between two genes and is expressed as a percentage. It is calculated by dividing the number of recombinant offspring by the total number of offspring and multiplying by 100.
In this case, the recombination frequency is:
(Number of recombinant offspring / Total number of offspring) x 100
Recombination frequency = (7 / 100) x 100 = 7%
8. Determine the distance between the genes in map units:
The map unit, also known as a centimorgan (cM), is a unit of genetic distance. It represents a 1% recombination frequency. To determine the distance between the genes in map units, divide the recombination frequency by 1.
In this case, the distance between the genes in map units is 7 cM.
By following these steps, you should be able to answer the questions and understand the process of determining the traits of the recombinant offspring and calculating recombination frequency and genetic distances.