If a human has an extra copy of one pair of homologous
chromosomes, how many chromosomes will she have in total?

48 chromosomes

Explanation:

The genetic condition described in the question is referred to as ANEUPLOIDY, which is a chromosomal disorder. ANEUPLOIDY occurs when there is an extra or missing copy of a chromosome in the normal set of chromosomes. It occurs mainly due to the fusion of an abnormal gamete.

A karyotype shows that human cell consists of 46 chromosomes in total I.e. 22 pairs of body and 1 pair of sex chromosomes. A human is a diploid organism I.e. contains two set of chromosomes. This means that one set of chromosomes (haploid, 23 chromosomes) is contributed by one parent.

Therefore, in a case whereby, an extra copy of a pair of homologous chromosomes is contained in the genome of a human. Hence, this will be 2n + 2 which means 46 chromosomes plus two extra chromosomes = 48 chromosomes. This ANEUPLOIDY likely resulted from the fusion of two abnormal gametes that are n+1 each.