The lineage of pea plants produced round seeds for four generations. The plants that fertilized these pea plants also produced round seeds. However, in the fifth generation, the plant produced to two plants with wrinkled seeds. Can that be possible? Explain your answer using your pedigree chart.

When two heter0zyg0us individuals are crossed -simple d0minant inheritance-, or a heter0zyg0us individual is crossed with a h0m0zyg0us recessive one, they can produce h0m0zyg0us recessive subjects among the progeny. Heter0zyg0us individuals among the fourth generation got crossed with another plant (h0m0zyg0us recessive or heter0zyg0us) and produced two h0m0zyg0us recessive plants expressing wrinkle seeds.

The first step is to understand the given information. So,

The first four generations produced round seeds

Plants that fertilized these plants also produced round seeds (see generation II)  

Among the fifth generation there are two plants with wrinkled seeds

Let us assume that a diallelic gene determines the shape of seeds.

D0minant allele R codes for round seeds

Recessive allele r codes for wrinkle seeds

Now, let us analyze the pedigree. According to the information provided here, we can tell that

black figures represent h0m0zyg0us d0minant individuals,

grey figures represent heter0zyg0us individuals

empty figures represent h0m0zyg0us recessive individuals

Remember that Generations are represented with roman numbers.

We will name the plants with numbers from 1 to 26.

According to the information in the statement and the information in the pedigree, we can say that grey individuals from the fourth generation are heter0zyg0us expressing round seeds. They can produce wrinkle seeds, if they are fertilized by another heter0zyg0us plant or a h0m0zygous recessive one.

Option 1:

Two heter0zyg0us plants are crossed, and their offspring have wrinkled seeds.

Option 2:

One heter0zyg0us plant is crossed with a h0m0zyg0us recessive one, and their offspring have wrinkled seeds. Let us see the cross

Look at the attached files for a better understanding      

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Explanation: