AP Biology Unit 5 heredity: a concept map you can edit, from meiosis to dihybrid crosses

Where Unit 5 sits in the course

AP Central's AP Biology course page (read November 2, 2026) lists eight units and gives Unit 5, Heredity, 8%–11% of the multiple-choice section, the lowest range in its table, level with Unit 1. That page gives the weighting only, and we could not read the full course and exam description in a usable form, so we don't list the unit's official topics here. The board follows the heredity chapters of OpenStax Biology 2e instead (meiosis, Mendel's crosses, non-Mendelian patterns), and the board's Ask in class list is where you add whatever else your teacher covers. Nothing here claims what a particular exam question will look like.

Meiosis: one cell in, four different gametes out

The top section of the board is a three-oval drawing: a 2n cell, then two n cells after meiosis I, then four n cells after meiosis II. Following OpenStax Biology 2e section 11.1 (read November 2, 2026), meiosis is one round of DNA replication followed by two divisions. Meiosis I is the reductional division: homologous chromosomes separate and the cells go from diploid to haploid. Meiosis II is like mitosis: sister chromatids separate.

Two cards under the drawing hold the two sources of variation from meiosis I. Crossing over happens in prophase I, when nonsister chromatids of a homologous pair swap pieces; the crossings are visible as chiasmata. Independent assortment happens at metaphase I, when the homologous pairs line up in random orientation, so n pairs can make 2^n different gametes. For humans, n = 23, which OpenStax puts at over 8 million.

The dihybrid cross: 16 squares you can read

The middle section is the cross OpenStax uses in section 12.3: seed colour (yellow Y is dominant to green y) and seed texture (round R is dominant to wrinkled r), with both parents YyRr. Each parent makes four equally likely gametes, YR, Yr, yR and yr, so the grid has 16 squares. We coloured each square by phenotype: black for round and yellow, blue for round and green, teal for wrinkled and yellow, red for wrinkled and green.

The card under the grid makes the link to the product rule: colour alone is 12 yellow to 4 green, which is 3:1, and texture alone is 12 round to 4 wrinkled, which is also 3:1. Because the two genes sort independently, the two ratios multiply. OpenStax adds that for more than two genes the Punnett square gets unwieldy and the forked-line or probability method is preferred. With four heterozygous genes, for example, the share that is homozygous recessive at all four is (1/4)^4 = 1/256, and the share that shows the dominant phenotype at all four is (3/4)^4 = 81/256. The board's self-quiz asks for the first of those.

Where the simple ratios stop working

The bottom section has four cue cards, each joined by an arrow to its note, so they stay together when you move them. The notes paraphrase OpenStax Biology 2e sections 12.2 and 12.3 (read November 2, 2026).

• Incomplete dominance. A red snapdragon crossed with a white one gives pink offspring, and pink crossed with pink gives 1 red : 2 pink : 1 white, so the phenotype ratio matches the genotype ratio instead of 3:1.
• Codominance. In the MN blood groups, heterozygotes express both alleles equally. The genotype ratio from a heterozygote cross is still 1:2:1, and the phenotype ratio matches it.
• X-linked genes. Thomas Hunt Morgan mapped the white-eye trait in fruit flies to the X chromosome in 1910. Males have only one X, so one recessive allele shows, and reciprocal crosses give different ratios.
• Linked genes. Genes close together on the same chromosome tend to be inherited as a pair, which breaks independent assortment; recombination can still separate them.

Beside the map, a Mix-ups list collects the pairs that get confused: segregation versus independent assortment, 3:1 versus 1:2:1, meiosis I versus meiosis II, and why dominant and recessive don't describe an X-linked male the way they do a female.

Build your own, step by step

1. 1Draw meiosis first, from memory, with the number of chromosome sets under each stage. Then open the cards and check it against your textbook.
2. 2Pick one cross from your notes and write out the gametes before filling the grid. Colour or tick squares by phenotype and count them before you write the ratio.
3. 3Check the ratio a second way, with the product rule, one gene at a time. If the two methods disagree, one has a mistake.
4. 4Add one card per pattern your teacher has covered, and join it to the rule it breaks.
5. 5Add a Mix-ups list every time a quiz question catches you, and an Ask in class list for what the book can't settle.
6. 6To study, cover the cards, redo the meiosis row, list the gametes for YyRr and explain 9:3:3:1 as 3:1 times 3:1. Tick what you can do and redo the rest tomorrow.

Cards, lists and sections can be dragged, so you can regroup the same cards by chapter or by exam topic. The grid on the board is hand-drawn ink, so for your own crosses you will draw a new grid, or write the squares as a list of cards.

Where something else is better

• Instructor-made maps are better when your teacher grades from one. If your course supplies a map, use it as your checklist and build yours beside it.
• Flashcard decks are better for memorising vocabulary such as the stages of meiosis. A map shows how ideas connect; it doesn't quiz you.
• Practice problems and past free-response questions are better for the exam itself. The board holds what you have learned and doesn't test you.
• A paper notebook is better if your class expects hand-drawn Punnett squares on paper and you work faster that way.
• Your textbook and teacher are the authority. This is a student-made summary of OpenStax, not College Board material, and the board has no answer key.

What Instaboard doesn't do

• No Punnett square tool, no cross calculator, no practice questions and no answer key. Squares are text or hand-drawn ink that the board doesn't understand.
• No AI and no auto-layout. The ready board is a layout to copy, and you move the cards yourself.
• No handwriting search and no conversion of handwriting to text. The eraser removes a whole stroke at a time.
• Editing needs a free sign-in. Viewing a board by link doesn't. If you are under 18, check with a parent or your school before you sign up for anything.
• The free plan is 5 boards and 150 items (cards, lists, images, text boxes; pen strokes, sections and arrows don't count), with 3 images and 1 file per board. This example uses about 30 items, so one board per unit works better than one per topic.
• No import from other note apps. Full-board PDF export works only on drawing boards and trip planners; for a card board, selected cards and lists can be saved as an image.
• Changes made offline are kept and sync when you're back online, but it isn't an offline-first app.

Questions