Random assortment (independent assortment) is the random orientation of homologous chromosome pairs during metaphase I of meiosis, so each gamete gets a unique mix of maternal and paternal chromosomes. It's one of the main sources of genetic diversity (EK 5.2.A.1).
Random assortment is the idea that when homologous chromosome pairs line up at the cell's middle during metaphase I, which one faces which pole is totally random. The maternal copy of chromosome 1 might go left while the maternal copy of chromosome 2 goes right, or both could go the same way. Each pair decides independently. When the pairs split in anaphase I, the chromosomes get sorted into gametes in a fresh combination every time.
The payoff is variety. EK 5.2.A.1 says correct separation gives each gamete a haploid (1n) set that's "an assortment of both maternal and paternal chromosomes." For a human with 23 chromosome pairs, that randomness alone produces 2^23 (over 8 million) possible chromosome combinations from a single person, before crossing over even adds more. That's why no two of your gametes are guaranteed to be alike.
This lives in Unit 5: Heredity, specifically Topic 5.2 (Meiosis and Genetic Diversity), and it's one of the mechanisms behind learning objective AP Bio 5.2.A: explain how meiosis generates genetic diversity. Genetic variation is the raw material evolution acts on, so this idea reaches forward into natural selection later in the course. If you can name random assortment, crossing over, and random fertilization as the three big variation-makers and say what each one does, you've got the core of 5.2 locked down.
Keep studying AP® Biology Unit 5
Crossing Over (Unit 5)
Both create gamete diversity, but at different scales. Random assortment shuffles whole chromosomes during metaphase I; crossing over (in prophase I) swaps pieces between non-sister chromatids, mixing alleles within a chromosome. Together they multiply the variation.
Anaphase I (Unit 5)
Anaphase I is the moment the randomly-oriented homologous pairs actually pull apart and head to opposite poles. The orientation set up in metaphase I gets locked in here, which is why this is meiosis I, not meiosis II, that drives assortment.
Random Fertilization (Unit 5)
Random assortment makes each gamete unique; random fertilization then randomly pairs one egg with one sperm. Stack the two together and the number of possible offspring genotypes explodes way past 8 million squared.
Genetic Variation and Natural Selection (Units 5, 7)
Random assortment is upstream of evolution. It supplies the genetic variation that natural selection later sorts, connecting Heredity directly to the evolution unit.
Multiple-choice questions like to ask the primary outcome (genetic variation among gametes) and which phase is responsible (metaphase I / anaphase I of meiosis I). Watch for stems that line up random assortment, crossing over, and random fertilization and ask you to pick the one happening at a specific phase. A classic trap question describes "non-sister chromatids exchanging DNA in prophase I" and asks for the term, the answer there is crossing over, not random assortment. No released FRQ has used the exact phrase, but FRQs on AP Bio 5.2.A reward you for explaining multiple sources of diversity, so be ready to describe random assortment in your own words as one of them.
Both boost gamete diversity but they're different events. Crossing over happens in prophase I and physically exchanges DNA segments between non-sister chromatids of a homologous pair. Random assortment happens at metaphase I and is just the random orientation of whole pairs, no DNA swapping involved. If the question mentions exchanging or recombining segments, it's crossing over.
Random assortment is the random orientation of homologous chromosome pairs at metaphase I, so maternal and paternal chromosomes get sorted into gametes in unpredictable combinations.
It happens in meiosis I, not meiosis II, because that's when homologous pairs separate.
In humans, random assortment alone produces over 8 million (2^23) possible chromosome combinations per gamete.
It's one of three diversity sources in Topic 5.2, alongside crossing over and random fertilization.
Each homologous pair orients independently of every other pair, which is why the term is also called independent assortment.
The variation it creates feeds directly into evolution, since natural selection acts on genetic variation.
It's the random way homologous chromosome pairs line up during metaphase I of meiosis, so each gamete ends up with a unique mix of maternal and paternal chromosomes. It's a major source of genetic variation under learning objective AP Bio 5.2.A.
No. Crossing over (prophase I) physically swaps DNA segments between non-sister chromatids of a homologous pair. Random assortment (metaphase I) just randomly orients whole chromosome pairs without exchanging any DNA. Both increase diversity, but only crossing over recombines segments.
Metaphase I and anaphase I. Pairs orient randomly at the metaphase plate in metaphase I, then separate to opposite poles in anaphase I. This is all within meiosis I, not meiosis II.
With 23 chromosome pairs, random assortment alone gives 2^23, which is over 8 million possible chromosome combinations per gamete. Crossing over and random fertilization push the real number far higher.
It generates genetic variation, and natural selection acts on variation. So the shuffling that happens in meiosis is what gives populations the differences that evolution can later select among, linking Unit 5 heredity to the evolution units.
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