Question

In a diploid species of plant, the genes for plant height and fruit shape are syntenic and separated by 18 m.u. Allele D produces tall plants and is dominant to d for short plants, and allele R produces round fruit and is dominant to r for oval fruit.
A plant with the genotype Dr/dR produces gametes. Identify gamete genotypes, label parental and recombinant gametes, and give the frequency of each gamete genotype.


A)Parental: 9\% DR, 9\% dr; recombinant: 41\% Dr, 41\% dR.

B)Parental: 41\% DR, 41\% dr; recombinant: 9\% Dr, 9\% dR.

C)Parental: 41\% Dr, 41\% dR; recombinant: 9\% DR, 9\% dr.

D)Parental: 9\% Dr, 9\% dR; recombinant: 41\% DR, 41\% dr.

Answer 1

Answer:

C)Parental: 41% Dr, 41% dR; recombinant: 9% DR, 9% dr.

Explanation:

The notation Dr/dR for genotypes means that one homologous chromosome has the alleles Dr and the other homologous chromosome has the alleles dR.

The heterozygous plant  Dr/dR will produce 4 types of gametes: two identical to the chromosmes the individual has in its somatic cells (called parental), and two gametes which will be a mix of the alleles in the homologous chromosomes (called recombinant).

• Dr: parental
• dR: parental
• DR: recombinant
• dr: recombinant

To calculate the frequency of each type of gamete, we must use the formula:

Distance (map units) / 100 = frequency of recombination.

18 mu / 100 = 0.18.

The total frequency of recombination between the genes D and R is 0.18, but every time crossing over happens, two recombinant gametes are generated. Therefore, each recombinant gamete will have a frequency of 0.18/2=0.09 = 9%.

The frequency of parental gametes will be:

1 - frequency of recombinant gametes

1 - 0.18 = 0.82

But there are 2 parental gametes, so each of them will have a frequency of 0.82/2=0.41 = 41%.