Q15.3-1CC - Campbell Biology

Question

When two genes are located on the same chromosome, what is the physical basis for the production of recombinant offspring in a testcross between a dihybrid parent and a double-mutant (recessive) parent?

Step-by-Step Solution

Answer

Heterozygous parents produce the gametes with recombinant genotypes for the two genes. It takes place via crossing over in meiosis I. The recombinant phenotype is produced from the fertilization of the recombinant gamete from a double mutant parent.

Step 1: Description of chromosomes

The thread-like structure present in the cell nucleus with DNA wound in it is known as a chromosome. It is passed from the parent to the offspring. The genetic information is coded in it and passed to the offspring. 

Step 2: Description of recombinant offspring

The recombinant offspring are the offspring that possess different allele combinations compared to the parents. The recombination process produces recombinant offspring. The main aim of creating recombinant offspring is to increase genetic diversity.

Step 3: Physical basis for the production of recombinant offspring

Meiosis is the type of cell division that takes place in the germ cells. Crossing over occurs in meiosis I. The similar DNA sequences present in chromosomes cross over each other, resulting in the formation of recombinants.

The crossing-over process takes place in the heterozygous parent resulting in recombinant genotypes. Double mutant parent produces the offspring with the recombinant gametes via the process of fertilization. 

Hence, the crossing over is the mechanism that produces recombinant offspring.