The probability of a yellow-seed plant (YY) forming a Y gamete is % because the principle of segregation - one of each gene pair goes to a; it only has "Y" alleles.

The probability of a yellow-seed plant (YY) forming a Y gamete is 100% because the principle of segregation - one of allele each gene pair goes to a gamete; it only has "Y" alleles.

Explanation:

According to Mendel's principle of segregation, the alleles of a gene are segregated to different gametes during the process of gamete formation. It results in the fact that each gamete has only one allele for a particular gene. The genotype of the parent plant is "YY". This means that the plant is homozygous for the gene of seed color. All the gametes of this plant would have only one copy of the "Y" allele. Therefore, there are 100% chances that the given plant would produce all the gametes with the "Y" allele.