Figure 8 shows some characteristics of pea plants - Edexcel - GCSE Biology Combined Science - Question 4 - 2023 - Paper 1

The completed Punnett square is:

   wrinkled seeds
       
       R | r  
   ----------- 
       R | Rr | Rr  
       r | rr | rr  

The combinations show that the offspring can be either round seeds (Rr) or wrinkled seeds (rr).

The percentage of the offspring that will produce round seeds is 50%, as indicated by the completed Punnett square.

To calculate the ratio, first find the total number of plants:

Total = 133 (purple) + 46 (white) = 179 plants.

Now, calculate the ratio:

Ratio = 133 : 46, which simplifies to approximately 3 : 1 when rounded to the nearest whole number.

This cross produced some offspring with white flowers because both parent plants are heterozygous (Pp). Each parent contributes one allele to the offspring, and if both contribute the recessive allele (p), the offspring will have white flowers.

Pea plant cells are diploid, meaning they have two sets of chromosomes, totaling 14 chromosomes. However, during the formation of gametes, meiosis occurs, reducing the chromosome number by half, resulting in gametes with only seven chromosomes.

During fertilization in pea plants, the male gamete (pollen) fuses with the female gamete (ovule). This fusion restores the diploid number of chromosomes, creating a zygote that will develop into a new plant. This process ensures genetic variation as the alleles from both parents combine.