7.3 Artificial Selection

Artificial selection is when humans intentionally choose which individuals breed to produce desired traits (selective breeding/domestication). Examples: turning teosinte into maize, creating dog breeds using breed standards, or using genomic selection in crops. It acts on heritable phenotypic variation: humans pick parents with preferred traits, so those alleles become more common over generations. That can speed change but often reduces genetic diversity and can cause inbreeding depression (or be relieved by hybrid vigor). How it differs from natural selection: - Agent of selection: humans vs. environment/fitness pressures. - Goal: intentional, goal-directed trait improvement vs. survival/reproductive success in a given environment. - Speed and predictability: often faster and more directional in artificial selection. - Genetic consequences: can reduce diversity (stricter selection, pedigree use) or exploit heterosis in hybrids. For AP: link this to LO 7.3.A (humans affect variation). Review Topic 7.3 study guide for examples and exam-style practice (https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc). For more practice problems, check (https://library.fiveable.me/practice/ap-biology).

Humans use artificial selection to change traits in plants and animals for useful or desirable outcomes—like higher crop yields, specific dog breeds, faster-growing livestock, pest resistance, or convenient harvest traits (e.g., maize from teosinte). By repeatedly choosing parents with preferred phenotypes (selective breeding/domestication), humans shift allele frequencies and reduce or reshape genetic variation (LO 7.3.A; EK 7.3.A.1). This relies on heritability of traits and phenotypic selection; breeders also manage trade-offs like inbreeding depression (loss of fitness) versus hybrid vigor (heterosis) and now use genomic selection and pedigree analysis to speed improvement. On the AP exam, expect to explain how human choices affect diversity and connect selection to heritability and population change (Unit 7 content, 13–20% of the exam). For a focused review of examples and vocab, see the Topic 7.3 study guide (https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc); for broader Unit 7 review, visit (https://library.fiveable.me/ap-biology/unit-7). For extra practice, try the 1,000+ practice problems (https://library.fiveable.me/practice/ap-biology).

Artificial selection = humans choosing which individuals get to reproduce so certain traits become more common. It’s like natural selection but guided by people: farmers breed corn from teosinte, dog breeders pick parents to meet breed standards, and plant breeders use genomic selection to speed changes. Key AP ideas: artificial selection affects variation in a population (LO 7.3.A; EK 7.3.A.1). You should know terms like selective breeding, domestication, heritability (how much a trait is passed on), phenotypic selection, inbreeding depression (bad effects from too much related mating), and hybrid vigor/heterosis (offspring sometimes stronger). On the exam, expect to explain how human choices change allele frequencies and trade-offs (e.g., disease resistance vs. appearance). For a quick topic review check the AP Topic 7.3 study guide (https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc), the full Unit 7 overview (https://library.fiveable.me/ap-biology/unit-7), and practice problems (https://library.fiveable.me/practice/ap-biology) to drill examples.

Artificial selection is humans choosing which individuals breed based on desired phenotypes (selective breeding/domestication). That drives directional change in allele frequencies and usually reduces genetic diversity within the selected population because favored alleles increase and other alleles can be lost or fixed (EK 7.3.A.1). Repeated selection and small breeding pools cause inbreeding depression (more deleterious recessives expressed). However, different breeds can become more genetically distinct from each other (increased between-population diversity). Breeders sometimes use hybrid crosses to restore variation and get heterosis (hybrid vigor), or use genomic selection and pedigree analysis to manage heritability and retain useful variation. For AP exam review, focus on how artificial selection alters variation and fitness (Topic 7.3) and link to population-genetics ideas in Unit 7 (see the study guide: https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc). Want more practice? Try problems at https://library.fiveable.me/practice/ap-biology.

Artificial selection (selective breeding) is when humans choose parents with desirable heritable traits and breed them over generations to change a population’s phenotype—like domestication of dogs or maize from teosinte. It relies on existing genetic variation, heritability, phenotypic selection, and can cause inbreeding depression or be managed for hybrid vigor. This is the process in EK 7.3.A (LO 7.3.A). Genetic engineering directly alters an organism’s DNA in the lab—adding, deleting, or editing genes (even from other species) to create traits that might not exist in the breeding pool. It’s much faster and more precise than artificial selection and doesn’t depend on natural variation or many generations. For AP exam thinking: describe mechanisms (phenotypic selection vs. molecular change), consequences for diversity, and predict outcomes (e.g., faster trait introduction vs. potential loss of genetic diversity). For more on artificial selection examples and exam-style practice, see the Topic 7.3 study guide (https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc), the Unit 7 overview (https://library.fiveable.me/ap-biology/unit-7), and practice questions (https://library.fiveable.me/practice/ap-biology).

Artificial selection is just humans doing what natural selection does, but on purpose: you pick which individuals get to reproduce based on traits you want (phenotypic selection), so alleles for those traits increase in frequency over generations. If a trait has high heritability (strong genetic basis), you’ll see change faster—sometimes in a few generations (like crops or fast-breeding animals) and for complex traits it can take many generations. Classic examples: maize from teosinte and dog breeds—breeders chose parents with desired traits, shifting allele frequencies and creating new breeds or crop varieties. Artificial selection can reduce genetic diversity (inbreeding depression) or sometimes increase hybrid vigor if you cross different lines. On the AP exam this maps to LO 7.3.A / EK 7.3.A—expect questions about how human choices change variation and outcomes like domestication. For a focused review, see the Topic 7.3 study guide (https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc) and practice problems (https://library.fiveable.me/practice/ap-biology).

Use clear, classic examples you can explain quickly on the exam: - Maize from teosinte—dramatic morphological change through selective breeding (good for showing how humans alter allele frequencies and domestication). - Dog domestication and breed standards—shows selection on behavior and morphology, plus problems like inbreeding depression. - Crop improvement (wheat, rice)—artificial selection for yield, disease resistance; mention hybrid vigor (heterosis) vs. inbreeding. - Livestock breeding (dairy cows selected for high milk yield)—ties to heritability and genomic selection. - Laboratory/industrial strains (yeast, crops via pedigree analysis or genomic selection)—shows targeted phenotypic selection using genetics. On the AP exam, use these to address LO 7.3.A and EK 7.3.A.1: describe how human choices change variation, cite heritability/phenotypic selection, and mention trade-offs (inbreeding depression vs. hybrid vigor). For a quick review, see the Topic 7.3 study guide (https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc), the Unit 7 overview (https://library.fiveable.me/ap-biology/unit-7), and practice problems (https://library.fiveable.me/practice/ap-biology).

Dog breeds are a textbook example of artificial selection (EK 7.3.A.1). Humans chose dogs with specific heritable traits (size, coat, behavior) and bred those individuals, shifting allele frequencies in a population to produce distinct breeds and breed standards. That’s selective breeding/domestication: repeated phenotypic selection on heritable variation increases the traits you want but can reduce genetic diversity, causing inbreeding depression. Breeders now also use genomic selection and pedigree analysis to increase desirable traits or create hybrid vigor (heterosis) by crossing lines. On the AP exam, you should be able to explain how human-mediated selection changes variation within a population (LO 7.3.A) and link phenotype selection to heritability and population genetics. For a targeted review, check the Topic 7.3 study guide (https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc), the Unit 7 overview (https://library.fiveable.me/ap-biology/unit-7), and practice questions (https://library.fiveable.me/practice/ap-biology).

Artificial selection often reduces genetic diversity because humans pick only a few individuals with desired heritable traits to breed. That strong, directional selection (think breed standards or crop traits) increases frequency of selected alleles and removes other alleles—including rare ones—from the gene pool. Repeatedly breeding close relatives to fix traits (inbreeding) further shrinks allele variety and can cause inbreeding depression. Practices like pedigree selection or tight genomic selection speed this process by narrowing breeders to a small subset, creating a genetic bottleneck. Less diversity means reduced ability to adapt to new diseases or environments (opposite of hybrid vigor/heterosis). This is exactly what EK 7.3.A.1 and LO 7.3.A in the CED describe: humans affect variation through selective breeding. For review, see the Topic 7.3 study guide (https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc) and Unit 7 overview (https://library.fiveable.me/ap-biology/unit-7). For extra practice, try problems at (https://library.fiveable.me/practice/ap-biology).

When humans selectively breed, they intentionally change allele frequencies in a population’s gene pool by choosing which individuals reproduce. Traits with high heritability that match breed standards get favored, so alleles for those traits increase while others drop—reducing genetic variation within that population (EK 7.3.A.1; LO 7.3.A). Over many generations this can produce distinct domesticated breeds (maize from teosinte, dog breeds), but it also raises risks: inbreeding increases homozygosity and can cause inbreeding depression, while strong selection can eliminate rare alleles and lower adaptive potential. Breeders sometimes use hybrid vigor (heterosis) or genomic selection and pedigree analysis to restore performance or manage diversity. On the AP exam, be ready to explain changes in variation and allele frequencies and to connect artificial selection to population genetics ideas in Unit 7 (see the Topic 7.3 study guide: https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc; unit overview: https://library.fiveable.me/ap-biology/unit-7). For practice, check the 1000+ AP practice problems (https://library.fiveable.me/practice/ap-biology).

Artificial selection in agriculture is when humans choose which plants or animals reproduce to change traits in a population (EK 7.3.A.1). Farmers select for higher yield, disease resistance, taste, or size—think maize bred from teosinte, or dog breeds with specific behaviors. Methods include phenotypic selection (pick the best-looking individuals), pedigree analysis, and modern genomic selection that uses heritability and marker data to speed improvement. Trade-offs matter: intense inbreeding can raise desirable traits but cause inbreeding depression; crossing different lines can produce hybrid vigor (heterosis). On the AP exam, you should be able to explain how selective breeding alters allele frequencies and reduces or reshapes diversity (LO 7.3.A). For a focused review, see the Topic 7.3 study guide (https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc), the Unit 7 overview (https://library.fiveable.me/ap-biology/unit-7), and practice questions (https://library.fiveable.me/practice/ap-biology).

Short answer: traits don’t get “made” by breeders—they already exist in populations as heritable variation (from mutations, recombination, and different gene regulation). Artificial selection (selective breeding) simply changes allele frequencies by choosing which individuals reproduce. Over generations, rare mutations or new combinations of alleles can be amplified; polygenic traits or regulatory changes can produce new-looking phenotypes (e.g., maize from teosinte, or dog breeds). Heritability matters: if a trait is genetic, selection will shift the population. Extreme inbreeding can cause inbreeding depression; crossing lines can give hybrid vigor (heterosis). On the AP exam you should be able to explain that humans affect diversity by selecting heritable variation and altering allele frequencies (LO 7.3.A / EK 7.3.A.1). For a deeper review, see the Topic 7.3 study guide (https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc) and the Unit 7 overview (https://library.fiveable.me/ap-biology/unit-7). Want practice problems? Try the AP practice set (https://library.fiveable.me/practice/ap-biology).

Pros: Artificial selection (selective breeding/domestication) lets humans change allele frequencies to fix desirable, heritable traits (EK 7.3.A.1). It’s used for crop improvement (maize–teosinte), livestock breeding, breed standards, and genomic selection—you can increase yield, disease resistance, or specific phenotypes predictably using pedigree analysis and knowledge of heritability. On an FRQ, these are easy to describe and justify (claim → evidence → reasoning) and link to LO 7.3.A. Cons: It reduces genetic diversity, increases homozygosity and risk of inbreeding depression, and can eliminate alleles useful in changing environments. Artificial selection can cause unintended trade-offs (pleiotropy) and loss of wild-type variation. For FRQs, be ready to explain mechanisms (phenotypic selection, heritability, fixation) and predict consequences or propose experiments (science practices: explain, justify, predict). For quick review, see the Topic 7.3 study guide (https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc) and practice FRQs at (https://library.fiveable.me/practice/ap-biology).

Usually much faster. Artificial selection applies very strong, intentional directional selection (selective breeding, breed standards, genomic selection) so you can see measurable changes in a few generations—for fast-reproducing crops or insects that’s years; for livestock and dogs it’s often noticeable in decades; for major domestication shifts (maize from teosinte) it took many human generations. Natural selection can be slower because it’s unguided and depends on variable selection strength, generation time, heritability, and available variation—often thousands of years for large morphological shifts, though it can also be rapid (tens of generations) if selection is strong. For AP you should connect this to LO 7.3.A and EK 7.3.A: artificial selection alters variation within populations faster because humans impose consistent selection on heritable traits. For review, see the Topic 7.3 study guide (https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc) and practice problems (https://library.fiveable.me/practice/ap-biology).

Yes—artificial selection can be harmful to the selected species. By intentionally choosing parents for specific traits (selective breeding, breed standards, genomic selection), humans reduce genetic variation (EK 7.3.A.1). That loss of variation raises risks like inbreeding depression (more harmful recessive alleles expressed), decreased ability to adapt to new diseases or environments, and fixation of maladaptive traits (e.g., extreme body shapes that cause health problems). Even if a trait has high heritability, focusing only on that trait can trade off other fitness-related traits. Sometimes crossing lines restores hybrid vigor (heterosis), but that’s not always used. For AP purposes, connect this to LO 7.3.A: artificial selection affects population diversity. Want more examples and practice Qs? Check the Topic 7.3 study guide (https://library.fiveable.me/ap-biology/unit-7/artificial-selection/study-guide/YdhzRk9EPvFMpXZ8Cthc), the Unit 7 overview (https://library.fiveable.me/ap-biology/unit-7), and practice problems (https://library.fiveable.me/practice/ap-biology).