The basic unit of heredity made of tightly packed DNA, with X and Y chromosomes involved in sex determination, is a ______.

The basic unit of heredity made of tightly packed DNA, with X and Y chromosomes involved in sex determination, is a ______.

• A. Gene
• B. Chromosome
• C. Allele
• D. Genome

Answer: (B)

Chromosomes are the structures that carry genetic information, built from DNA tightly packed with proteins. The reference to X and Y chromosomes points directly to a chromosome, since those are the sex-determining chromosomes in many organisms. A gene is a specific segment of DNA on a chromosome that codes for a trait, but the clue describes the whole carrier rather than a single gene. A genome is the complete set of genetic material, not a single unit. An allele is a variant form of a gene, not a structural carrier. So the best answer is chromosome.

Chromosomes are the structures that carry genetic information, built from DNA tightly packed with proteins. The reference to X and Y chromosomes points directly to a chromosome, since those are the sex-determining chromosomes in many organisms. A gene is a specific segment of DNA on a chromosome that codes for a trait, but the clue describes the whole carrier rather than a single gene. A genome is the complete set of genetic material, not a single unit. An allele is a variant form of a gene, not a structural carrier. So the best answer is chromosome.