According to Mendel's Law of Segregation, how are alleles contributed to offspring?

• A. Alleles are inherited in complete blocks from a single parent
• B. Half of the alleles come from each parent
• C. All alleles are contributed by the mother
• D. Traits are inherited in pairs only

Answer: (B)

During meiosis, the two alleles for a gene separate so each gamete carries only one allele. When fertilization occurs, the offspring receives one allele from each parent, so half of the genetic contribution comes from the mother and half from the father. This combination restores two alleles in the zygote for every gene. For example, a parent with alleles A and a can pass on either A or a, and the other parent can pass on either A or a, leading to offspring with a mix of alleles. The other statements don’t fit because alleles aren’t inherited as complete blocks from one parent, not all from the mother, and inheritance isn’t limited to traits appearing in fixed pairs independent of this segregation.