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Unit 5 · Heredity Flashcards Cheat Sheet Essentials Visual Review MC Practice FRQ Practice

AP Biology Unit 5 Visual Review

A topic-by-topic visual walkthrough of Heredity — meiosis, sources of genetic diversity, Mendelian and non-Mendelian genetics, and environmental effects on phenotype.

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TOPIC 5.1 Meiosis 2ndiploid one parent cell Meiosis I → homologs split n n Meiosis II → sisters split n n n n 4 haploid gametes One diploid cell → TWO divisions → four genetically unique haploid cells. DNA is copied only ONCE (before meiosis I). Meiosis I — homologs separate The REDUCTION division: homologous chromosome pairs line up and separate, cutting the chromosome number in half (2n → n). This is what makes cells haploid. Crossing over happens here (prophase I). Homologs pair up as tetrads and swap segments — a major source of genetic diversity (Topic 5.2). Meiosis II — sister chromatids separate Similar to mitosis: the sister chromatids of each chromosome are pulled apart. No further reduction — the cells were already haploid. Result: 4 haploid gametes (sperm or egg) Fertilization later fuses two haploid gametes to restore the diploid (2n) number in the offspring. Meiosis halves the chromosome number (2n → n), making four haploid gametes for sexual reproduction. The Review Hub · AP Biology Unit 5 TOPIC 5.2 Meiosis & Genetic Diversity THREE SOURCES OF VARIATION IN OFFSPRING 1 · Crossing over prophase I Homologous chromosomes swap matching segments, making new allele combos. 2 · Independent assortment metaphase I or Each homologous pair lines up randomly → 2ⁿ possible combinations (2²³ in humans). 3 · Random fertilization at conception + Any one of millions of eggs can meet any one of millions of sperm — a unique zygote. Why diversity matters Genetic variation is the raw material for evolution. A varied population is more likely to contain individuals that survive environmental change — natural selection acts on this variation (Unit 7). Crossing over, independent assortment, and random fertilization make every offspring genetically unique. The Review Hub · AP Biology Unit 5 TOPIC 5.3 Mendelian Genetics MONOHYBRID CROSS Bb × Bb Bb BB Bb Bb bb Bb Genotype 1 : 2 : 1 · Phenotype 3 dominant : 1 recessive Law of segregation Each parent carries two alleles for a trait; they SEPARATE during meiosis so each gamete gets only ONE. Offspring get one from each parent. A dominant allele masks a recessive one. Law of independent assortment Alleles for DIFFERENT traits are inherited independently of one another (if on separate chromosomes). A dihybrid cross (RrYy × RrYy) gives the classic 9 : 3 : 3 : 1 phenotype ratio. Vocabulary to know cold Genotype = allele combination (BB, Bb, bb) · Phenotype = observable trait · Homozygous = two same alleles Heterozygous = two different alleles · A test cross (× homozygous recessive) reveals an unknown genotype. Alleles segregate into gametes and assort independently — a Bb × Bb cross gives a 3:1 phenotype ratio. The Review Hub · AP Biology Unit 5 TOPIC 5.4 Non-Mendelian Genetics Incomplete dominance Heterozygote is a BLEND of the two alleles. Example: red × white snapdragons → pink. Neither allele fully masks the other. Codominance BOTH alleles are fully expressed at once (not blended). Example: AB blood type shows both A and B antigens; roan cattle show both red and white hairs. Multiple alleles A gene has more than two possible alleles in the population. Example: human ABO blood type has three alleles — Iᴬ, Iᴮ, and i. Polygenic traits Many genes add up to control one trait, giving a smooth, continuous range (a bell curve). Examples: human height, skin color, eye color. Sex-linked & other patterns Sex-linked genes sit on the X chromosome — males (XY) show recessive X-linked traits more often (color blindness, hemophilia). Pleiotropy: one gene affects many traits. Epistasis: one gene masks another. Linked genes on the same chromosome tend to be inherited together (violating independent assortment). Many traits break Mendel's simple rules: blending, both-expressed, many genes, or sex-linked. The Review Hub · AP Biology Unit 5 TOPIC 5.5 Environmental Effects on Phenotype Phenotype = Genotype + Environment Temperature Himalayan rabbits & Siamese cats have dark fur only on cooler body parts (ears, paws) — a heat-sensitive pigment enzyme. Same genotype, different look. pH & chemistry Hydrangea flowers are blue in acidic soil and pink in basic soil — the same plant changes color with soil chemistry. Environment shapes the trait. Nutrition & more Human height depends on genes AND nutrition. Plants grown in shade vs. sun differ; identical twins raised apart show differences. Genes set a range, not a fixed value. Phenotypic plasticity The same genotype can produce different phenotypes depending on environmental conditions. Genes provide a RANGE of possibilities; the environment determines which one is expressed. Both nature AND nurture matter. An organism's traits come from its genes AND its environment — not genotype alone. The Review Hub · AP Biology Unit 5
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How to use the visual review

Spend 30 seconds per slide before clicking next. Look at the diagram, then ask yourself: "Could I draw this from memory and explain it?"

Use the fullscreen button () on desktop for the best experience. Use arrow keys to navigate. Tap "Show all slides" to jump around.

This is great for review the night before the exam — fast, visual, and covers everything you need to remember about Unit 5's genetics content.