Figure 12 shows some characteristics of pea plants - Edexcel - GCSE Biology - Question 6 - 2023 - Paper 1

The completed Punnett square for the cross between Rr (round seeds) and rr (wrinkled seeds) is as follows:

                |  r                |  r                
             -------------------
          R  |  Rr (round)      |  Rr (round)      
          r  |  rr (wrinkled)   |  rr (wrinkled)   

This shows that 50% of the offspring will produce round seeds.

The percentage of the offspring that will produce round seeds is 50%. This is derived from the Punnett square, where 2 out of the 4 combinations yield round seeds.

The ratio of offspring with purple flowers to white flowers is calculated as follows:

egin{align*} ext{Number of purple flowers} & : ext{Number of white flowers} \ 133 & : 46 \ ext{This simplifies to } rac{133}{46} ext{, which is approximately } 3:1. ext{Thus, rounded to the nearest whole number, the ratio is } 3:1. ext{Therefore, the final answer is } 3:1.

ewline ext{Hence,} ext{ratio: } 3:1.

It was possible for this cross to produce some offspring with white flowers because both parent plants were heterozygous (Pp), meaning they carried one allele for purple flowers and one for white flowers. Thus, when these plants crossed, there was a possibility of producing offspring with two recessive alleles (pp), resulting in white flowers.

Pea plant gametes have only seven chromosomes because they are produced by meiosis, a process that halves the chromosome number. Since the diploid cells of pea plants contain 14 chromosomes, the haploid gametes will each have half of that number, resulting in seven chromosomes.

At fertilisation, a male gamete (sperm) fuses with a female gamete (egg) to form a zygote. This fusion restores the diploid chromosome number, combining genetic material from both parents. The zygote then undergoes mitosis to develop into a new organism.