Crossing homozygous dominant and homozygous recessive organisms will only produce heterozygous offspring, while crossing heterozygous organisms will produce both heterozygous and homozygous offspring. This is due to the principle of independent assortment. The principle of independent assortment states that during meiosis, each pair of genes segregates independently of one another. This means that the alleles of one gene pair have no effect on the alleles of another gene pair being passed down to the offspring.

Example of a Cross That Will Only Produce Heterozygous Offspring

Consider a cross between an organism with the genotype BB (homozygous dominant) and an organism with the genotype bb (homozygous recessive). All of the offspring of this cross will be Bb, which is heterozygous for the trait. This is because the B allele (the dominant allele) will be passed down in all instances and the b allele (the recessive allele) will be passed down in all instances. The combination of both alleles in the same organism is what results in the heterozygous genotype.

Example of a Cross That Will Produce Heterozygous and Homozygous Offspring

Now consider a cross between an organism with the genotype Bb (heterozygous) and another organism of the same genotype. In this case, the offspring could be BB (homozygous dominant), Bb (heterozygous) or bb (homozygous recessive). This is because some of the gametes produced by the heterozygous parents will carry the B allele (the dominant allele) and some will carry the b allele (the recessive allele). When these gametes are combined, the combination of alleles in the offspring can be homozygous or heterozygous.

Conclusion

In summary, crossing homozygous dominant and homozygous recessive organisms will only produce heterozygous offspring, while crossing heterozygous organisms will produce both heterozygous and homozygous offspring. This is due to the principle of independent assortment, which states that during meiosis, each pair of genes segregates independently of one another.