Which role do gametes play in reproduction? a. they reorder the offspring’s genes. b. they increase the number of chromosomes in the offspring. c. they carry half of each parent’s chromosomes. d. they are formed by the joining of two zygotes.

C. Gametes are the sex cells, and each (sperm and ovum) contain half of the parent's genetic material. These cells will fuse to produce a zygote, which will usually contain the full number of genes required by an organism to live. If there is a chromosomal abnormality, such as a gamete with an extra chromosome, the offspring can either die in development or sometimes be born with physiological and/or developmental difficulties. An example of this phenomenon is trisomy 21, also known as Down Syndrome, in which the 21st chromosome bears 3 copies instead of the regular 2.