Genetics Quiz

Genetics quiz: mastering DNA, chromosomes, and heredity

Nested vocabulary: cell, nucleus, chromosome, DNA, gene, allele

The first challenge in this chapter is getting the scales in the right order. A human cell contains a nucleus; that nucleus contains 46 chromosomes grouped into 23 pairs; each chromosome is a long DNA molecule; a gene is a segment of DNA that codes for an inherited trait; and an allele is one of the possible versions of a given gene. Many students mix up these levels, so the quiz includes plenty of sorting questions to lock in the chain "cell > nucleus > chromosome > DNA > gene" for good.

DNA structure: double helix and A-T, G-C base pairing

DNA is a double-helix molecule made of two complementary strands. The nucleotide bases always pair up according to Watson and Crick's rule (1953): A with T, and G with C. This complementarity is why DNA can copy itself faithfully before every cell division—an essential mechanism for understanding mitosis, meiosis, and mutations. Several intermediate-level questions ask you to write out the complementary strand for a given sequence.

Mitosis vs. meiosis: never mix them up again

This is THE classic trap on science exams. Mitosis is a conservative division: a cell with 46 chromosomes produces two identical daughter cells, each with 46 chromosomes. It drives growth, healing, and tissue renewal. Meiosis, on the other hand, is a reductional division: it takes place in the reproductive organs and turns a cell with 46 chromosomes into four gametes with 23 chromosomes each, all genetically different. It's what makes genetic diversity in offspring possible. The quiz includes several direct-comparison questions, implicit diagrams, and real-world cases (healing = mitosis, egg production = meiosis).

Fertilization, heredity, crosses, and Mendel's laws

At fertilization, the egg (23 chromosomes) and the sperm cell (23 chromosomes) fuse to form the fertilized egg, or zygote (46 chromosomes). The child thus inherits half of their DNA from each parent, but the specific combination received is unique—except in identical twins from the same zygote. When it comes to alleles, there are two rules you absolutely need to remember: an AA × aa cross gives 100% Aa offspring with the dominant phenotype; an Aa × Aa cross gives 75% dominant phenotype and 25% recessive phenotype (Mendel's law). These ratios come up on nearly every science exam, sometimes disguised as a cystic fibrosis or blood type problem.

Mutations, genetic disorders, GMOs, and cloning

A mutation is an accidental change in the DNA sequence. It can be neutral, beneficial (a source of evolution), or harmful (a cause of disease). A mutation is only passed on to offspring if it affects a germ cell. As for disorders, the curriculum distinguishes between chromosomal abnormalities (Down syndrome: 47 chromosomes instead of 46) and single-gene disorders (cystic fibrosis: a mutation in one gene, with a normal karyotype). Finally, cloning produces a genetically identical copy of an existing organism, while GMOs are organisms whose DNA has been altered through genetic engineering. To connect these ideas to the history of species, check out our evolution quiz (coming soon).

Go further: science and middle school exams

Play in timed or daily mode

To practice under real test conditions, try the timed quiz: a set amount of time per question, ideal for building speed and instinct. And every day, the quiz of the day offers a fresh mix of questions at every level to keep your knowledge sharp without burning out.