Question

In the garden pea, tall vine (D) is dominant over dwarf (d), green pod (Y) is dominant over yellow (y) and round seed (W) is dominant over wrinkled (w). A tall, yellow, round plant is crossed to a dwarf, green, round one. The following ratios occurred in the F1 generation: 3/8 tall, green, round; 3/8 dwarf, green round; 1/8 tall, green, wrinkled; and 1/8 dwarf, green, wrinkled. What is the genotype of the two parental plants?

Answer 1

Answer:

3/8 tall, green, round

3/8 dwarf, green, round

Explanation:

The progeny which are in highest ratio represent parental plants.

Here in the given question, 3 out of 8 progeny are tall, green, round and 3 out of 8 progeny are dwarf, green, round which are the highest in number so they represent parental plants. The reason behind this is that during crossing over only two non-sister chromatids undergo crossing over while two other parental chromosomes remain intact. Out of the 4 chromosome types, 2 remain the same which will result in the same type of genotype of off-springs as of parents. So even if there is 100% chance of crossing over between non sister chromatids still only 50% will be recombinants rest of the 50% will represent parental type.

Another case may be when two genes are very near to each other then it is quite possible that the genes may not undergo crossing over at all in that case there will be no recombinants at all.

So, it simply means that parentals > recombinants or the progeny which are highest in number represent parentals.

In case of unlinked genes, parentals = recombinants.  But, recombinants can never be greater than parentals.