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

The completed Punnett square is as follows:

        R      r
      __________
   R |   Rr   | Rr   |
      |________|______|
   r |   rr    | rr    |
      |________|______|

This shows the genetic combinations of the offspring from the cross.

From the completed Punnett square, we can see that there are 2 squares showing round seeds (Rr) out of 4 total squares. Therefore, the percentage of the offspring that will produce round seeds is 50%.

To find the ratio of offspring with purple flowers to those with white flowers, we can calculate:

• Number of purple flowered plants: 133
• Number of white flowered plants: 46

Thus, the ratio is:

$ext{Ratio} = \frac{133}{46} \approx 2.89 \text{ (rounded to whole number)} = 3:1$

This cross produced some offspring with white flowers because both parents were heterozygous (Pp). Each parent had one allele for purple flowers (P) and one allele for white flowers (p). Thus, some of the offspring could inherit the two recessive alleles (pp), resulting in white flowers.

Pea plants are diploid, meaning they have two sets of chromosomes (14 total). However, gametes are produced through meiosis, which reduces the chromosome number by half. As a result, pea plant gametes only have 7 chromosomes.

During fertilization, the male gamete (pollen) fuses with the female gamete (ovule) to form a zygote. This zygote will undergo division and develop into a new plant. Fertilization restores the diploid state by combining the genetic material from both gametes, resulting in a complete set of chromosomes.