Question

In a dihybrid cross, SsYy x SsYy, what fraction of the offspring will be homozygous for both traits?

Answer 1

A dihybrid cross is basically defined as the mating experiment between two individual organisms that are identically hybrid for any two traits. A hybrid organism is defined as the one that is heterozygous, which means that it should carry two different alleles at a particular genetic locus.

Complete answer:
The dihybrid cross which is clearly given in this question is:
SsYy X SsYy
According to the law of independent assortment, both the plants in dihybrid cross will be producing these 4 gametes:
SY, Sy, sY and sy
The genotypes of the offspring by the fusion of gametes produced by any two plants can easily be calculated by the method known as the checkerboard method.
There are a total 16 possible combinations. Out of these 16 possible outcomes, 4 combinations will have genotype homozygous for both the given traits, which does not depend on the dominant or recessive allele. These combinations are given below:
SSYY, SSyy, ssYY and ssyy. or can be written as SYSY, SySy, sYsY and sysy
Thus 1/4th fraction of the population will definitely be homozygous for both the given traits.
This fraction will always be approximate because the observed results are always closer to the calculated value as these are based on the law of probability.

Note:
Mendel was the one who laid down the basic groundwork in the field of genetics and eventually led to the proposal of the laws of inheritance. Law of Segregation, Law of Independent Assortment and Law of Dominance are the three laws of inheritance which were given by Gregor Mendel. These laws were proposed as a result of his experiments on the pea plant with different types of traits.