Human eggs and sperm each contain 23 ________, which are composed of long strands of ________.

• A. genes; RNA
• B. nuclei; lipids
• C. alleles; protein
• D. chromosomes; DNA

Answer: (D)

Verified step by step guidance

1. Understand the question: The problem is asking about the components of human eggs and sperm, specifically the structures and molecules they contain.
2. Recall the basic biology of human gametes: Human eggs and sperm are haploid cells, meaning they contain half the number of chromosomes compared to somatic (body) cells. Each gamete contains 23 chromosomes.
3. Review the structure of chromosomes: Chromosomes are composed of tightly coiled DNA (deoxyribonucleic acid), which carries genetic information in the form of genes.
4. Eliminate incorrect options: Analyze the provided choices. 'Genes; RNA' is incorrect because genes are segments of DNA, not RNA. 'Nuclei; lipids' is incorrect because nuclei are cellular structures, not genetic material, and lipids are not involved in genetic information storage. 'Alleles; protein' is incorrect because alleles are variations of genes, and proteins are not the structural material of chromosomes.
5. Select the correct answer: The correct answer is 'chromosomes; DNA' because human eggs and sperm each contain 23 chromosomes, which are composed of long strands of DNA.