According to Mendel, the selfing of a dihybrid (A/a.B/b) will result in four groups of phenotypically different offspring (9/16 dominant-dominant; 3/15 dominant-recessive; 3/16 recessive-dominant; 1/16 recessive-recessive for the two aits involved). In additional to experimental errors, please list 2 different reasons at make one unable to observe the 9:3:3:1 ratio. Solution (1) For each of the seven pairs of characters examined, it was observed that one allelomorph dominated over the other, so that F1 exhibits one or the other alternative phenotypes represented in the parents. However, soon after rediscovery of Mendel\'s laws, experiments were available to show tha tin some cases the F1 individual showed the phenotype which was intermediate between the two parents. For instance in four-o\'clock plant (Mirabilis jalapa) it was found that when plants wiht red flowers were crossed with those having white flowers, plants with pint flowers were obtained in F1 generation. This would then give rise to red, pink and white flowered plants in 1:2:1 ratio in the F2 generation. Similarly in Snapdragon, plants with broad leaves and plants with narrow leaves give reise to plants with intermediate leaves in F1 generation. Likewise, plants plants with red flowers and plants with white flowers give rise to those with pink flowers. If a dihybrid cross is made using broad leaves and red flowers in one parent (BBRR) and narrow leaves and white flowers in the other parent (bbrr), F1 individuals (BbRr) will have intermediate leaves with pink flowers. In the F2 generation nine phenotypes corresponding to nine genotypes will be observed. (2) According to the Law of Independent Assortment, any two or more than two pairs of characters assort independently of each other. Exception to this phenomenon were discovered due to linkage and the associated phenomenon of crossing over. (3) In each of the seven pairs of characters studied by Mendel, there were only tow laternative forms for each character. This meant that only two alleles were present for each character. This also led to a belief that for each character there were two alternative forms, one dominant over the other. Later work showed that for a character there can be several phenotypes e.g. for rabbits the body can be of four or more types. Therefore, concept of alternative allelomorphs had to be modified by the concept of multiple allelism..

1. According to Mendel, the selfing of a dihybrid (A/a.B/b) will result in four groups of
phenotypically different offspring (9/16 dominant-dominant; 3/15 dominant-recessive; 3/16
recessive-dominant; 1/16 recessive-recessive for the two aits involved). In additional to
experimental errors, please list 2 different reasons at make one unable to observe the 9:3:3:1
ratio.
Solution
(1) For each of the seven pairs of characters examined, it was observed that one allelomorph
dominated over the other, so that F1 exhibits one or the other alternative phenotypes represented
in the parents. However, soon after rediscovery of Mendel's laws, experiments were available to
show tha tin some cases the F1 individual showed the phenotype which was intermediate
between the two parents. For instance in four-o'clock plant (Mirabilis jalapa) it was found that
when plants wiht red flowers were crossed with those having white flowers, plants with pint
flowers were obtained in F1 generation. This would then give rise to red, pink and white
flowered plants in 1:2:1 ratio in the F2 generation. Similarly in Snapdragon, plants with broad
leaves and plants with narrow leaves give reise to plants with intermediate leaves in F1
generation. Likewise, plants plants with red flowers and plants with white flowers give rise to
those with pink flowers. If a dihybrid cross is made using broad leaves and red flowers in one
parent (BBRR) and narrow leaves and white flowers in the other parent (bbrr), F1 individuals
(BbRr) will have intermediate leaves with pink flowers. In the F2 generation nine phenotypes
corresponding to nine genotypes will be observed.
(2) According to the Law of Independent Assortment, any two or more than two pairs of
characters assort independently of each other. Exception to this phenomenon were discovered
due to linkage and the associated phenomenon of crossing over.
(3) In each of the seven pairs of characters studied by Mendel, there were only tow laternative
forms for each character. This meant that only two alleles were present for each character. This
also led to a belief that for each character there were two alternative forms, one dominant over
the other. Later work showed that for a character there can be several phenotypes e.g. for rabbits
the body can be of four or more types. Therefore, concept of alternative allelomorphs had to be
modified by the concept of multiple allelism.