In order to solve the problem, trace the colorblind allele all the way to the grandparent's alleles. It is possible that the daughter is a carrier, but this is not a guarantee. Males can not be carriers, as they only have one X chromosome; they either have the allele or they do not. Finally, the maternal grandmother may be colorblind, but this is not guaranteed.

All that we know is that at least one of the maternal grandmother's alleles codes for colorblindness. The maternal grandmother passed this allele to the mother. The color blind son inherits his Y chromosome from his father, and his only X chromosome from his mother; thus, the mother must be a carrier to pass down a color blind X chromosome to the son.

If cell division occurs incorrectly, and the resulting cell contains an abnormal number of chromosomes, that cell is considered to be aneuploid. Polyploidy is the presence of an entire extra copy of the genome in a cell. Euploid (true ploid) refers to a cell with the correct number of chromosomes.

Linked genes are found on the same chromosome, and do not always separate according to independent assortment. Alleles are different versions of a gene. Codominance is a mode of inheritance in which both alleles, if present, are fully expressed.

Although X-linked dominant traits tend to be rare, it is certainly possible that the boy would inherit it from an affected mother. A father only gives a Y chromosome to his sons. This means that the boy could not inherit the X-linked dominant trait from his father.

Since the cell has a total of 23 chromosomes it must be a gamete. Recall that the diploid number for humas is 2n=46. The presence of a Y chromosome means that it corresponds to a male gamete so it must be a sperm cell.  

Autosomes are all the chromosomes that do not determine an individual's sex. X and Y chromosomes both determine sex, and are sex chromosomes. The other 22 pairs of chromosomes are autosomes. 

The union of two gametes is called fertilization, which results in a zygote. The zygote is a diploid cell that will grow into the entire organism.

A haploid cell has only one set of chromosomes as compared to the two sets normally found in diploid cells. In a haploid cell there are 22 autosomes and 1 sex chromosome for a total of 23 chromosomes.   

Haploid cells have 23 chromosomes each (22 autosomes and 1 sex chromosome) so when they fuse the resulting cell will have 46 chromosomes (44 autosomes and 2 sex chromosomes). This idea is demonstrated during fertilization, where two haploid cells (gametes) fuse to form the zygote, which is diploid.

A somatic cell is a diploid cell so it will have 22 pairs of autosomes and one pair of sex chromosomes for a total of 46 chromosomes.