Misconception 1: "Dominant means more common in a population"

Correct: Dominant alleles can be rare; recessive alleles can be common. Frequency in populations depends on selection, drift, and mutation — not dominance. Example: Huntington's disease is dominant but rare; blue eyes are recessive but common in some populations.

Misconception 2: "F1 hybrids must look intermediate between parents"

Correct: F1 shows only the dominant trait (complete dominance). An intermediate phenotype in F1 indicates incomplete dominance — a special case, not the general rule.

Misconception 3: "Traits skip generations"

Correct: Recessive traits appear to "skip" generations only because carriers (heterozygotes) don't express them. The allele is present in every intermediate generation; it simply isn't expressed in heterozygotes.

Misconception 4: "Crossing over happens after chromosomes separate"

Correct: Crossing over occurs during Prophase I (pachytene), while homologs are PAIRED (synapsed). It cannot happen after separation. Chiasmata are the physical crossover points visible in Prophase I.

Misconception 5: "Mendel worked with 7 genes on 7 chromosomes by design"

Correct: It was partly coincidental (or he may have discarded data from linked traits). Peas have 7 chromosome pairs, and 7 traits happened to be on different chromosome pairs. Later research showed some are on the same chromosome but far enough apart to appear unlinked.

Misconception 6: "A test cross is always with a dwarf (tt) plant"

Correct: A test cross is with any homozygous RECESSIVE individual. "tt" is just the symbol for homozygous recessive. For the ABO system, the equivalent would be ii (blood group O). For any gene, the homozygous recessive is the tester.

Misconception 7: "Co-dominance and incomplete dominance both produce blended phenotypes"

Correct: Only incomplete dominance produces a BLENDED phenotype (new intermediate colour). Co-dominance produces BOTH phenotypes simultaneously — no blending. AB blood group shows BOTH A and B antigens distinctly on the same RBC.

Misconception 8: "Recombination frequency directly equals physical distance in base pairs"

Correct: Genetic distance (cM) and physical distance (base pairs) are not directly proportional. Recombination rates vary across chromosomes (higher near telomeres, lower near centromeres). One cM is approximately 1 Mb on average in humans, but this varies greatly by region.

Misconception 9: "Epistasis means one gene is 'better' than another"

Correct: Epistasis means one gene MASKS or MODIFIES the expression of another gene. It has nothing to do with gene "quality" — it is a functional interaction where one gene's product suppresses or is required for the other gene's phenotypic expression.

Misconception 10: "All offspring in a test cross will be exactly 1:1"

Correct: Expected ratio is 1:1, but actual numbers always deviate due to sampling error (chance variation). Exact 1:1 ratios are only theoretical expectations for infinitely large samples. Statistical tests (chi-square) determine if deviations are significant.

Misconception 11: "Multiple alleles mean multiple genes"

Correct: Multiple alleles = multiple variants of ONE gene. All ABO variants ($I^A$, $I^B$, i) are alleles of the same gene locus on chromosome 9. Multiple genes (different loci) = polygenic inheritance — a completely different concept.

Misconception 12: "$I^A$ $I^B$ blood group shows incomplete dominance"

Correct: $I^A$ $I^B$ is CO-DOMINANCE, not incomplete dominance. Both antigens (A and B) are present fully and separately — not blended. The person does not have a "partial A + partial B antigen" — they have COMPLETE A and COMPLETE B antigens simultaneously.

Misconception 13: "Sickle cell anemia is polygenic"

Correct: Sickle cell anemia is caused by ONE gene (HbS allele of the beta-globin gene). Its multiple effects make it an example of PLEIOTROPY. Polygenic would mean multiple genes all contributing to the anaemia, which is not the case here.

Misconception 14: "The Law of Independent Assortment applies to all diploid organisms"

Correct: It applies only to genes on different chromosomes, in any organism. Linked genes (same chromosome) violate it in ALL organisms, not just peas or Drosophila.

Misconception 15: "Self-pollination cannot produce heterozygotes"

Correct: Self-pollination of a heterozygote (Tt) produces 1 TT : 2 Tt : 1 tt offspring — 50% are still heterozygous after the first generation of selfing. Only after multiple generations of selfing does the proportion of heterozygotes decrease toward zero. True-breeding requires many generations of self-pollination.

Misconception 16: "A person with blood group A can never have a child with blood group B"

Correct: If a person with blood group A is heterozygous ($I^A$ i) and partners with someone who is $I^B$ i (group B), a child can have blood group B ($I^B$ i). The child's blood group B allele came from the other parent, not from the A parent.