Final answer:
A polar body cell from a rat contains 21 chromosomes, which is the haploid number for rats. This is half the diploid number found in rat somatic cells, with oogenesis leading to the formation of haploid cells.
Step-by-step explanation:
The total number of chromosomes in a polar body cell from a rat is haploid, meaning it contains one set of chromosomes. During the process of oogenesis, the unequal cell division produces three polar bodies that typically degrade and one haploid ovum. It is critical to note that the number of chromosomes in a polar body must correspond to the species-specific haploid number. Rats (Rattus norvegicus), like humans, have a diploid number of 42 chromosomes in their somatic cells, meaning each haploid gamete or polar body would have 21 chromosomes.