One DNA replication is followed by two divisions. Meiosis I separates homologs; meiosis II separates sister chromatids.
Common trap: A sister chromatid is a copied chromosome component, not the homolog inherited from the other parent.
UNIT 05 / REVIEW
Heredity
Your alleles have commitment issues.
Active recall activities40 original questions · 7 topics
DNA replication→
Meiosis I→
Meiosis II→
Gametes
Use this overview to connect processes. Review the details below for mechanisms and exceptions.
Crossing over, independent assortment, and random fertilization reshuffle existing alleles. Mutation creates new alleles.
Common trap: Independent assortment describes how different homolog pairs orient, not sister chromatids randomly forgetting where to go.
Alleles segregate into gametes. For independent events, multiply probabilities for “and” and add mutually exclusive outcomes for “or.”
Common trap: Dominant does not mean common, stronger, or selectively favored. It describes a heterozygote phenotype.
Incomplete dominance gives an intermediate heterozygote phenotype; codominance shows both allele products. Multiple genes and the environment can influence a trait.
Common trap: An intermediate phenotype does not mean the parental alleles permanently blended. They can segregate unchanged into the next generation.
Inheritance predictions depend on chromosome location. In a standard XX/XY model, a father passes his X to daughters and his Y to sons.
Common trap: A father does not pass an X-linked allele to a son in the standard XX/XY model. The son gets the father’s Y.
Nearby loci on the same chromosome tend to be inherited together. Recombination frequency = recombinant offspring ÷ total offspring × 100%.
Common trap: A 50% recombination frequency does not prove genes are on different chromosomes. Widely separated loci on one chromosome can give the same result.
Failure of homologs or sister chromatids to separate can produce aneuploid gametes. Use pedigrees and statistical tests as evidence, with explicit assumptions.
Common trap: Failure to reject a hypothesis does not prove it true. Also, an extra copy of one chromosome is not an extra complete chromosome set.
Keep going
Original review notes informed by standard biology principles. Check the official AP Biology framework ↗ and OpenStax Biology 2e ↗ for further reading.