---
title: "Heredity and Traits"
book: "Primary & Middle School Biology"
subject: biology
language: en
chapter: 63
exercises: 12
source: https://one-course.com/books/biology/1/en/chapter/63-heredity-and-traits
---

# Chapter 63 — Heredity and Traits

Family photographs are [biology](https://one-course.com/books/biology/1/en/chapter/1-living-or-not-living#def-g1-living-or-not-living) data. Grandmother’s chin on the toddler, the mother’s curls on neither child, one brother tall and one not — resemblance runs in families, and so does difference. This book has leaned on the fact for years ([Remark 23.3](https://one-course.com/books/biology/1/en/chapter/23-how-animals-reproduce#rem-g4-animal-reproduction-mix)’s foal, [Proposition 54.5](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#prop-g8-sexual-reproduction-shuffle)’s siblings); this year’s opening chapter finally studies it: what exactly is inherited, what is not, and what the patterns of family resemblance let us conclude.

![Biology data, sepia edition: resemblance and difference, running down the generations.](https://one-course.com/images/onecourse/chapters/biology-1/g9-heredity-and-traits/img-c4a431742655.jpg)

*[Biology](https://one-course.com/books/biology/1/en/chapter/1-living-or-not-living#def-g1-living-or-not-living) data, sepia edition: resemblance and difference, running down the generations.*

## 63.1 Traits, and where they come from

**Definition 63.1 (Traits).**

A *trait* is any describable characteristic of an individual: [eye](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) color, [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) group, earlobe shape, height, a singing voice, a scar. The individual’s whole collection of traits is built by two workings: what was *inherited*, and what the *[environment](https://one-course.com/books/biology/1/en/chapter/37-exploring-our-environment#def-g6-exploring-our-environment-components) and life* added ([Definition 28.1](https://one-course.com/books/biology/1/en/chapter/28-adapted-to-their-world#def-g4-adapted-to-their-world-adaptation)’s world, acting on one body).

**Definition 63.2 (Heredity).**

*Heredity* is the transmission of [traits](#def-g9-heredity-and-traits-traits) from parents to offspring through reproduction — through, as [Chapter 54](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#ch-g8-sexual-reproduction) showed, two single [cells](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell). [Traits](#def-g9-heredity-and-traits-traits) that pass this way are *hereditary*: [eye](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) color and [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) group are; scars and pierced [ears](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) are not, however long worn. The sorting test is the [gametes](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#def-g8-sexual-reproduction-gametes): what two [cells](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell) cannot carry, families cannot transmit.

**Example 63.3 (Sorting a family album).**

Grandfather’s photographs: his distinctive nose — [hereditary](#def-g9-heredity-and-traits-heredity), there it is again on the aunt and the cousin; his weathered farmer’s tan — acquired, his office-working grandson lacks it; his height — partly both, for the grandson overtops him on the same frame, fed by richer years ([Proposition 18.1](https://one-course.com/books/biology/1/en/chapter/18-a-balanced-diet#prop-g3-balanced-diet-jobs)); his violin skill — not [hereditary](#def-g9-heredity-and-traits-heredity) as skill ([Example 60.6](https://one-course.com/books/biology/1/en/chapter/60-nervous-communication#ex-g8-nervous-communication-juggler): [synapses](https://one-course.com/books/biology/1/en/chapter/60-nervous-communication#def-g8-nervous-communication-synapse) are trained, not transmitted), though the musical family tells us something subtler is at work in what is passed on: perhaps aptitude, never the trained wiring itself.

**Proposition 63.4 (Inherited and acquired).**

The two workings separate on three tests:

1. *family pattern* : [hereditary traits](#def-g9-heredity-and-traits-heredity) recur through the tree along reproduction’s lines; acquired ones follow lives (all the sailors weathered, whoever their parents);
2. *presence from the start* : [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) group is fixed at [fertilization](https://one-course.com/books/biology/1/en/chapter/31-from-flower-to-fruit#def-g5-flower-to-fruit-steps) ; the tan and the skill are built after;
3. *transmission* : children of amputees have their [limbs](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-parts) ; children of bodybuilders start untrained. Acquired [traits](#def-g9-heredity-and-traits-traits) die with their acquirer — the [gametes](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#def-g8-sexual-reproduction-gametes) do not carry them.

Most visible [traits](#def-g9-heredity-and-traits-traits) — height, build, even temperament — are woven of both workings, inherited range and lived filling-in.

**Proof.** *Admitted at this level.* ∎

## 63.2 Reading family patterns

**Example 63.5 (Traits that skip).**

Some patterns puzzle at first sight: two brown-eyed parents with a blue-eyed child; grandmother’s [trait](#def-g9-heredity-and-traits-traits) absent in every child yet returning in a grandchild. Skipping is common, and it carries a heavy conclusion: a parent can *transmit what they do not show*. The [trait](#def-g9-heredity-and-traits-traits)’s instructions traveled hidden through a generation — so what is inherited is not the [trait](#def-g9-heredity-and-traits-traits) itself but something that *determines* it, carriable unseen.

**Proposition 63.6 (What the patterns force us to conclude).**

Three conclusions, each forced by an observation:

1. since acquired [traits](#def-g9-heredity-and-traits-traits) do not pass, what passes must be *determinants* — instructions for building [traits](#def-g9-heredity-and-traits-traits) , not the [traits](#def-g9-heredity-and-traits-traits) themselves;
2. since [traits](#def-g9-heredity-and-traits-traits) skip generations, the determinants can be *carried without showing* : each individual carries more than it displays;
3. since every child receives from both parents by two [gametes](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#def-g8-sexual-reproduction-gametes) ( [Proposition 54.2](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#prop-g8-sexual-reproduction-core) ), each parent contributes a *selection* of its determinants — and the selections differ from child to child, or siblings would match ( [Proposition 54.5](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#prop-g8-sexual-reproduction-shuffle) ’s shuffle, now located: it is a shuffle *of determinants* ).

**Proof.** *Admitted at this level.* ∎

**Remark 63.7 (The question this sets).**

The family album has cornered us into a marvelous question. Somewhere in a [sperm cell](https://one-course.com/books/biology/1/en/chapter/57-the-reproductive-systems#def-g8-reproductive-systems-male)’s almost-nothing ([Example 57.2](https://one-course.com/books/biology/1/en/chapter/57-the-reproductive-systems#ex-g8-reproductive-systems-sperm) — a packed [nucleus](https://one-course.com/books/biology/1/en/chapter/45-the-cell-unit-of-life#def-g6-cell-unit-of-life-parts) and a tail) travel instructions for a nose, a [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) group, an [eye](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) color — carriable unshown, selectable by halves, readable by the growing body. *Where are they, and what are they made of?* The sperm’s anatomy already points the answer: everything the father sends fits in a [nucleus](https://one-course.com/books/biology/1/en/chapter/45-the-cell-unit-of-life#def-g6-cell-unit-of-life-parts) ([Remark 29.6](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#rem-g5-first-look-at-cells-nucleus) promised that spot mattered). The next two chapters open it.

**Method 63.8 (Auditing a trait).**

For any [trait](#def-g9-heredity-and-traits-traits), run the three tests:

1. map it on the family tree: does it follow reproduction’s lines, or lives and habits?
2. date it: fixed from the start, or built along the way?
3. apply the [gamete](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#def-g8-sexual-reproduction-gametes) test: could two [cells](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell) carry it? (a scar cannot; a [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) group can);
4. verdict: inherited, acquired, or — commonest — an inherited range, lived into.

## 63.3 Exercises

**Exercise 63.1 ★.**

Define [trait](#def-g9-heredity-and-traits-traits) and [heredity](#def-g9-heredity-and-traits-heredity), and give the sorting test in one phrase.

**Solution of Exercise 63.1.**

A [trait](#def-g9-heredity-and-traits-traits) is any describable characteristic of an individual; [heredity](#def-g9-heredity-and-traits-heredity) is the transmission of [traits](#def-g9-heredity-and-traits-traits) from parents to offspring through reproduction. The sorting test: what two [gametes](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#def-g8-sexual-reproduction-gametes) cannot carry, families cannot transmit.

**Exercise 63.2 ★.**

Classify: [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) group; a pierced [ear](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense); freckles; fluent French; earlobe shape.

**Solution of Exercise 63.2.**

[Blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) group: [hereditary](#def-g9-heredity-and-traits-heredity). Pierced [ear](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense): acquired. Freckles: [hereditary](#def-g9-heredity-and-traits-heredity) tendency, sun-lived (both workings). Fluent French: acquired. Earlobe shape: [hereditary](#def-g9-heredity-and-traits-heredity).

**Exercise 63.3 ★.**

State the three tests of [Proposition 63.4](#prop-g9-heredity-and-traits-sorting).

**Solution of Exercise 63.3.**

Family pattern (recurs along reproduction’s lines, or follows lives); presence from the start (fixed at [fertilization](https://one-course.com/books/biology/1/en/chapter/31-from-flower-to-fruit#def-g5-flower-to-fruit-steps), or built after); transmission (passes to children, or dies with its acquirer).

**Exercise 63.4 ★.**

Why do children of bodybuilders start untrained? What does that show?

**Solution of Exercise 63.4.**

Because trained [muscle](https://one-course.com/books/biology/1/en/chapter/17-bones-and-muscles#def-g3-bones-and-muscles-muscle) is acquired — built by use, not carried by [gametes](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#def-g8-sexual-reproduction-gametes). It shows that what a life adds to a body is not written into what reproduction transmits.

**Exercise 63.5 ★.**

What does a skipping [trait](#def-g9-heredity-and-traits-traits) prove a parent can do?

**Solution of Exercise 63.5.**

Transmit what they do not show: the [trait](#def-g9-heredity-and-traits-traits)’s determinant traveled through them hidden, and surfaced a generation on.

**Exercise 63.6 ★.**

Why must what is inherited be determinants rather than [traits](#def-g9-heredity-and-traits-traits)? One sentence.

**Solution of Exercise 63.6.**

Because [traits](#def-g9-heredity-and-traits-traits) themselves (a chin, a [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) group) cannot ride in two single [cells](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell) — what rides must be instructions for building them.

**Exercise 63.7 ★★.**

Height ran taller in the grandson on the same frame. Untangle the two workings in that sentence.

**Solution of Exercise 63.7.**

Inherited: the height range the frame suggests — the grandson received the family’s determinants. Lived: richer feeding filled the range further — the [environment](https://one-course.com/books/biology/1/en/chapter/37-exploring-our-environment#def-g6-exploring-our-environment-components)’s addition on top of the inheritance.

**Exercise 63.8 ★★.**

Explain why siblings differ, in determinant language — and why identical twins ([Exercise 58.10](https://one-course.com/books/biology/1/en/chapter/58-from-egg-cell-to-birth#exo-g8-from-egg-to-birth-10)) do not.

**Solution of Exercise 63.8.**

Each child receives a different selection of each parent’s determinants — the shuffle deals fresh combinations per [fertilization](https://one-course.com/books/biology/1/en/chapter/31-from-flower-to-fruit#def-g5-flower-to-fruit-steps). Identical twins split *after* one [fertilization](https://one-course.com/books/biology/1/en/chapter/31-from-flower-to-fruit#def-g5-flower-to-fruit-steps): one deal, two builds — so their determinant sets match.

**Exercise 63.9 ★★.**

Run [Method 63.8](#met-g9-heredity-and-traits-audit) on: (a) a family’s recurring early gray hair; (b) a football player’s stamina.

**Solution of Exercise 63.9.**

(a) Follows the tree, appears at its family age regardless of trade or town, conceivably gamete-carried: [hereditary](#def-g9-heredity-and-traits-heredity). (b) Built by training, follows the sport not the parents, no [gamete](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#def-g8-sexual-reproduction-gametes) carries stamina: acquired — on an inherited range of build and [heart](https://one-course.com/books/biology/1/en/chapter/27-the-heart-and-the-blood#def-g4-heart-and-blood-heart) ([Proposition 49.7](https://one-course.com/books/biology/1/en/chapter/49-organs-at-work#prop-g7-organs-at-work-training) builds what [heredity](#def-g9-heredity-and-traits-heredity) only sketches).

**Exercise 63.10 ★★.**

The violin case: what could the musical family be transmitting, if never the trained skill? Distinguish carefully.

**Solution of Exercise 63.10.**

Never the skill — [synapses](https://one-course.com/books/biology/1/en/chapter/60-nervous-communication#def-g8-nervous-communication-synapse) train in each life anew. What may pass: aptitude’s raw materials — [ear](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense), dexterity, temperament — an inherited range that musical households then fill with practice, tuition and example (the second, living-together channel of transmission).

**Exercise 63.11 ★★.**

Two brown-eyed parents, a blue-eyed child — and the neighbor doubts the family. Defend the family with [Example 63.5](#ex-g9-heredity-and-traits-skip)’s logic.

**Solution of Exercise 63.11.**

Skipping is [heredity](#def-g9-heredity-and-traits-heredity) behaving normally: each parent can carry the [blue-eye](https://one-course.com/books/biology/1/en/chapter/5-the-five-senses#def-g1-the-five-senses-sense) determinant unshown and hand it on; two such hidden copies meeting in one child display the [trait](#def-g9-heredity-and-traits-traits). The pattern proves carriage-without-showing — not anything about the family’s honesty.

**Exercise 63.12 ★★★.**

From the [sperm cell](https://one-course.com/books/biology/1/en/chapter/57-the-reproductive-systems#def-g8-reproductive-systems-male)’s anatomy alone ([Example 57.2](https://one-course.com/books/biology/1/en/chapter/57-the-reproductive-systems#ex-g8-reproductive-systems-sperm)), argue where the father’s determinants must sit — and what size that implies for the instructions of a whole human.

**Solution of Exercise 63.12.**

Everything the father transmits rides in the [sperm cell](https://one-course.com/books/biology/1/en/chapter/57-the-reproductive-systems#def-g8-reproductive-systems-male), and the [sperm cell](https://one-course.com/books/biology/1/en/chapter/57-the-reproductive-systems#def-g8-reproductive-systems-male) is a tail and a packed [nucleus](https://one-course.com/books/biology/1/en/chapter/45-the-cell-unit-of-life#def-g6-cell-unit-of-life-parts) — so the determinants must sit in the [nucleus](https://one-course.com/books/biology/1/en/chapter/45-the-cell-unit-of-life#def-g6-cell-unit-of-life-parts). And since a whole human’s paternal instructions fit in a package thousandths of a millimetre across, the instructions must be written at molecular smallness — a script finer than any [cell](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell) structure the school [microscope](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-microscope) shows.

## 63.4 Problem: The Village Genealogist

**Problem 63.1.**

Weekend problem — three generations, one trait ledger

A village genealogist annotates the parish’s family trees with [traits](#def-g9-heredity-and-traits-traits): the “chapel chin” (a distinctive chin recurring for a century), left-handedness, the bakers’ floury [lung](https://one-course.com/books/biology/1/en/chapter/47-how-animals-breathe#def-g7-how-animals-breathe-four) cough, [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) groups from the donation register, and the shepherds’ weathered faces.

**Part I — Sorting the ledger.**

1. Sort the five [traits](#def-g9-heredity-and-traits-traits) by [Method 63.8](#met-g9-heredity-and-traits-audit) , with the deciding test for each.
2. The cough follows the bakery, not the family: marrying in brings it, moving away loses it. Which test is this, in action?
3. The chapel chin skips the middle generation in two [branches](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-tree) . Draw the conclusion it forces.
4. [Blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) groups sometimes surprise the register: a group-O child of group-A and group-B parents. What must each parent have carried?

**Part II — The determinant reading.**

5. Rewrite the chin’s century in determinant language: what actually traveled down four generations, in what vehicles ( [Definition 63.2](#def-g9-heredity-and-traits-heredity) )?
6. Why do the chin-carrying cousins differ in everything else? Locate the shuffle.
7. The genealogist finds no case — in a century — of a scar, a trade or a language passing to a newborn. State the generalization, and its mechanism-level reason.
8. One family’s twins match to the chin and beyond. What does the ledger conclude about their beginning ( [Remark 32.7](https://one-course.com/books/biology/1/en/chapter/32-human-reproduction#rem-g5-human-reproduction-twins) )?

**Part III — The lecture.**

9. The genealogist lectures: “the parish transmits two inheritances — one by [gametes](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#def-g8-sexual-reproduction-gametes) , one by living together.” Assign the ledger’s five [traits](#def-g9-heredity-and-traits-traits) to the two channels.
10. “Each of us displays less than we carry.” Defend from the ledger, twice.
11. A listener asks what the [gamete](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#def-g8-sexual-reproduction-gametes) channel’s instructions are physically. Give the honest answer of [Remark 63.7](#rem-g9-heredity-and-traits-question) — location known, contents next chapter.
12. Close the lecture with the audit’s one-line verdict on the commonest case: most [traits](#def-g9-heredity-and-traits-traits) are *what* , lived *how* ?

**Solution of Problem 63.1.**

**1.** Chapel chin: [hereditary](#def-g9-heredity-and-traits-heredity) (family pattern, present from the start). Left-handedness: [hereditary](#def-g9-heredity-and-traits-heredity) tendency (follows families loosely, fixed early). Bakers’ cough: acquired (follows the trade). [Blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) groups: [hereditary](#def-g9-heredity-and-traits-heredity) (fixed at [fertilization](https://one-course.com/books/biology/1/en/chapter/31-from-flower-to-fruit#def-g5-flower-to-fruit-steps), gamete-carriable). Weathered faces: acquired (follow the shepherding life).

**2.** The family-pattern test: the [trait](#def-g9-heredity-and-traits-traits) maps onto an occupation’s lines, not reproduction’s — marrying in acquires it, moving away loses it, no [gamete](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#def-g8-sexual-reproduction-gametes) involved.

**3.** That a determinant can be carried without being shown: the middle generation transmitted the chin’s instructions while displaying other chins.

**4.** Each parent carried, alongside its shown group’s determinant, a hidden group-O determinant — and the child received the two hidden ones. Carriage unshown, in the register’s own ink.

**5.** Not the chin but its determinants — instructions for building it — traveling in the only vehicles reproduction has: one [egg cell](https://one-course.com/books/biology/1/en/chapter/23-how-animals-reproduce#def-g4-animal-reproduction-sexual) and one [sperm cell](https://one-course.com/books/biology/1/en/chapter/57-the-reproductive-systems#def-g8-reproductive-systems-male) per generation, four handovers in the century.

**6.** In the selections: each [fertilization](https://one-course.com/books/biology/1/en/chapter/31-from-flower-to-fruit#def-g5-flower-to-fruit-steps) dealt the shared chin determinant alongside a fresh half-and-half selection of everything else — common card, different hands.

**7.** Acquired [traits](#def-g9-heredity-and-traits-traits) are never transmitted. Reason: they are built in the body’s tissues by living, and the [gametes](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#def-g8-sexual-reproduction-gametes) — two [cells](https://one-course.com/books/biology/1/en/chapter/29-a-first-look-at-cells#def-g5-first-look-at-cells-cell), carrying determinants only — have no way to record them.

**8.** One [fertilization](https://one-course.com/books/biology/1/en/chapter/31-from-flower-to-fruit#def-g5-flower-to-fruit-steps), later split: a single determinant deal built twice — [Remark 32.7](https://one-course.com/books/biology/1/en/chapter/32-human-reproduction#rem-g5-human-reproduction-twins)’s identical twins, certified by the ledger’s matching.

**9.** [Gamete](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#def-g8-sexual-reproduction-gametes) channel: chin, [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) groups, left-handedness’s tendency. Living-together channel: the cough (the bakery’s air), the weathering (the hills’ weather) — and, from the album chapter, languages, trades and skills.

**10.** From the skips: the middle generation carried the chin unshown. From the [blood](https://one-course.com/books/biology/1/en/chapter/25-the-journey-of-food#prop-g4-journey-of-food-absorb) register: A- and B-showing parents carried O unshown. Twice over, carriage exceeds display.

**11.** Physically: they sit in the [gametes](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#def-g8-sexual-reproduction-gametes)’ nuclei — that much the sperm’s anatomy already proves. What they are made of, and how so small a package writes so large a book, is precisely the next chapters’ question.

**12.** Most [traits](#def-g9-heredity-and-traits-traits) are inherited ranges, lived into: the [gametes](https://one-course.com/books/biology/1/en/chapter/54-sexual-reproduction#def-g8-sexual-reproduction-gametes) deal the sketch, the life draws it in.