The answer is c. alleles that are carried on X and Y chromosomes.
Sex-linked traits are those traits which inheritance depends on sex chromosomes. Sex chromosomes are X and Y. Women have two X chromosomes, while men have one X and one Y chromosome. One those chromosomes are genes responsible for some sex-linked traits. As genes on the other chromosomes, genes on sex chromosomes as well have different forms called alleles. Therefore, alleles that are carried on X and Y chromosomes (sex chromosomes) best describe sex-linked traits.
Different rate of synapse production in different areas of the brain indicate that:
1. the different areas of the brain does not develop at the same time.
2. there is difference in timing of development of different skills and behavior categories and
3. different rate of synapses elimination occur in the brain.
The human brain start maturing before birth and continue to grow until about the age of twenty five. Even after this age, adult brain continues to mature as a result of the learning experiences that people are exposed to.
The REM is meant to produce specific proteins