A certain plant homozygous for yellow seeds and red flowers was crossed with a plant homozygous for green seeds and white flowers. The F1 plants had yellow seeds and pink flowers. The F1 plants were selfed to get F2 progeny. Assuming independent assortment of the two characters, how many phenotypic categories are expected for these characters in the F2 generation?
Parent generation (P) : One parent is homozygous for yellow seeds (dominant trait, represented by 'YY') and red flowers (dominant trait, represented by 'RR'). Therefore, this parent's genotype is YYRR. The other parent is homozygous for green seeds (recessive trait, represented by 'yy') and white flowers (recessive trait, represented by 'rr'). Therefore, this parent's genotype is yyrr. First filial generation (F1) : When these two parents cross, all of the offspring in the F1 generation will inherit one allele from each parent for both traits, leading to a genotype of YyRr. This genotype results in a phenotype of yellow seeds and pink flowers (as red is incompletely dominant over white, resulting in pink when both are present). Second filial generation (F2) : Now, when these F1 generation plants self-fertilize, we can get a range of genotypes. This is due to the law of independent assortment which states that the alleles for yellow/green seeds and the alleles for red/pink/white flowers will sort independently of each other into the gametes. For each trait, the F1 parent can produce four types of gametes (YR, Yr,yR,yr). The Punnett square method can be used to find out the different combinations of these gametes. However, many of these combinations will lead to the same phenotypes due to the dominance of certain traits. If we only look at the different phenotypes (physical appearances), we get: Yellow seeds and red flowers Yellow seeds and pink flowers Yellow seeds and white flowers Green seeds and red flowers Green seeds and pink flowers Green seeds and white flowers These are the 6 different phenotypes expected in the F2 generation.