If a pea plant has a genotype sstt, what are the possible genetic combinations that could be present in a single grain of pollen produced by the plant?

Pollen is essentially a male plant germ cell .

Like all germ cells it is produced in the process of meiosis. In this process, the diploid cells (cells that have two sets of chromosomes) divide into two haploid cells (cells that have one set of chromosomes).

In our example, the diploid mother cell has a SS Tt genotype. This essentially means that the cell has two alleles of the same gene on a different chromosome in the chromosome pair.

When the cell divides, it can give only one allele to the haploid cell.

For the S gene, this cell has two identical dominant alleles( SS genotype), therefore, it can only give the dominant allele to the haploid cell.

As for the T gene, this cell has two different alleles, one dominant and one recessive (Tt genotype) and therefore can give either the dominant (T) or the recessive (t) allele to the haploid germ cell (the pollen).

So, the possible genetic combinations are

ST if the dominant T allele is passed

St if the recessive t allele is passed

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the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.