In a male individual with Down's syndrome (trisomy 21), how many chromosomes would be visible at metaphase I of spermatogenesis?

In a male individual with Down's syndrome, also known as trisomy 21, there is an extra copy of chromosome 21, leading to a total of 47 chromosomes in somatic cells. During spermatogenesis, particularly at the metaphase I stage of meiosis, the cells are still diploid, meaning they contain two copies of each chromosome, except for the one involved in the trisomy.

At metaphase I, homologous chromosomes pair up and align at the metaphase plate. In the case of this individual with Down's syndrome, there will be pairs of chromosomes for each of the 22 autosomes plus an additional chromosome from the anomalous pair involving chromosome 21, which results in one of those pairs having an extra chromosome.

Therefore, during metaphase I of spermatogenesis for this individual, a total of 47 chromosomes would be visible. This includes 46 chromosomes from the standard diploid configuration, plus the additional chromosome resulting from the trisomy. This is why 47 chromosomes would be visible at this stage of spermatogenesis.