EigoPro 1級読解 — The Ghost in the Genome: Epigenetics and the Limits of Lamarck

Few ideas in contemporary biology have been as eagerly conscripted into popular narrative as epigenetics—the study of heritable changes in gene expression that do not alter the underlying DNA sequence. Chemical marks such as DNA methylation and histone modification act as molecular punctuation, dictating which genes are read aloud and which are silenced, and they can persist as cells divide. Because these marks respond to the environment—diet, stress, toxins—the temptation has been irresistible to declare that Lamarck, long ridiculed for proposing that organisms transmit acquired characteristics, has been vindicated. The blacksmith's children, it is whispered, may inherit his sinews after all. Such enthusiasm outruns the evidence. The decisive obstacle is the germline. In mammals, epigenetic marks are largely erased in two sweeping waves of reprogramming—once in the developing germ cells and again shortly after fertilization—so that each generation begins, in effect, with a wiped slate. A handful of loci appear to evade this scouring, and a few rodent studies report effects rippling across two or three generations, but extrapolating from such anomalies to robust, sequence-independent inheritance in humans remains speculative. What looks like inherited memory may merely be a shared environment perpetuating itself. The more defensible claim is subtler and, arguably, more profound. Epigenetics dissolves the tidy dichotomy between nature and nurture by furnishing a mechanism through which experience is biochemically inscribed upon the genome's regulatory apparatus—even if that inscription is, for the most part, reset rather than bequeathed. To mistake plasticity for heredity is to confuse the instrument for the score. The genome is not a fixed text but a manuscript perpetually annotated; the annotations, however, are seldom passed to one's heirs intact.

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この単元の問題を3問、解説つきで公開しています

1級 · 読解 · 全5問

問 1

What is the central argument of the passage?

Because DNA methylation and histone modification do not change the genetic sequence, they have no meaningful biological consequences.
Epigenetics has decisively rehabilitated Lamarck's theory by proving that acquired characteristics are reliably passed to offspring.
The distinction between nature and nurture should be abandoned because the environment alone determines which genes are expressed.
While epigenetics reveals how the environment can shape gene expression, claims that it confirms the inheritance of acquired traits are largely overstated.

Phrase

Such enthusiasm outruns the evidence.

1級読解主旨把握論旨

⚡ひとことで

エピジェネティクスは環境の影響を示すが、獲得形質の遺伝の証明という主張は誇張だと論じる。

選択肢の解説Choice Analysis

「While epigenetics reveals how the environment can shape gene expression, claims that it confirms the inheritance of acquired traits are largely overstated.」

正解

筆者は冒頭でエピジェネティクスへの過熱した期待を紹介しつつ、"Such enthusiasm outruns the evidence" と転換し、生殖細胞系列での消去を理由に遺伝の主張を退ける。一方で環境が遺伝子発現に刻まれる仕組み自体は認める。この「示すが、しかし誇張」という二段構えが論旨の核心である。

「Epigenetics has decisively rehabilitated Lamarck's theory by proving that acquired characteristics are reliably passed to offspring.」
= 獲得形質が確実に遺伝すると証明された ━ 筆者は "extrapolating from such anomalies ... remains speculative" と述べ、復権の主張を明確に否定している。。
「Because DNA methylation and histone modification do not change the genetic sequence, they have no meaningful biological consequences.」
= 化学修飾は生物学的意味を持たない ━ 本文は methylation/histone が遺伝子の読み上げを左右すると明記しており、無意味どころか中心的役割を認めている。。
「The distinction between nature and nurture should be abandoned because the environment alone determines which genes are expressed.」
= 環境のみが遺伝子発現を決めると主張 ━ 筆者は nature/nurture の二分法を「溶かす」と言うのみで、環境単独の決定論は唱えていない。。

▦Collocation

パターン	意味	例
outrun the evidence	証拠を超えて先走る	Their conclusions outrun the evidence available.
heritable change	遺伝しうる変化	Epigenetics studies heritable changes in expression.
acquired characteristic	獲得形質	Lamarck proposed the transmission of acquired characteristics.
gene expression	遺伝子発現	Methylation regulates gene expression.
confirm a theory	理論を裏づける	The data do not confirm the theory as claimed.

❝例文

The hype around the discovery outruns the evidence.
その発見をめぐる誇大宣伝は証拠を超えて先走っている。
Epigenetic marks can persist as cells divide.
エピジェネティックな標識は細胞分裂を経ても残りうる。
He overstated the implications of a single study.
彼は一つの研究の含意を誇張した。

💡Tip · 覚えるコツ

主旨問題では「賛成も反対も両方含む」選択肢が正解になりやすい。本文の転換語 (such enthusiasm outruns...) を見つけ、筆者が肯定と留保のどちらに重心を置くか確認しよう。

問 2

According to the passage, why do epigenetic marks generally fail to be passed across generations in mammals?

They are confined entirely to somatic cells and never appear in germ cells at any stage.
They are largely erased during two waves of reprogramming, once in the germ cells and again after fertilization.
They alter the underlying DNA sequence so drastically that the changes cannot survive cell division.
They are chemically too unstable to persist even within the lifetime of a single organism.

Phrase

two sweeping waves of reprogramming

1級読解詳細把握

⚡ひとことで

哺乳類では生殖細胞と受精後の二度の再プログラミングでほぼ消去されるため。

選択肢の解説Choice Analysis

「They are largely erased during two waves of reprogramming, once in the germ cells and again after fertilization.」

正解

本文は "epigenetic marks are largely erased in two sweeping waves of reprogramming—once in the developing germ cells and again shortly after fertilization" と明記する。各世代が「白紙」から始まることが遺伝を阻む決定的障害 (the decisive obstacle is the germline) とされている。

「They alter the underlying DNA sequence so drastically that the changes cannot survive cell division.」
= 配列を大きく変えて分裂に耐えない ━ エピジェネティック標識は定義上 DNA 配列を変えない (do not alter the underlying DNA sequence) ので前提が誤り。。
「They are confined entirely to somatic cells and never appear in germ cells at any stage.」
= 生殖細胞には一切現れない ━ 本文は生殖細胞でこそ標識が消去されると述べており、生殖細胞に標識が存在することを前提にしている。。
「They are chemically too unstable to persist even within the lifetime of a single organism.」
= 個体の生涯すら持続できない ━ 本文は "can persist as cells divide" と述べ、個体内での持続性を明確に認めている。。

▦Collocation

パターン	意味	例
wave of reprogramming	再プログラミングの波	Two waves of reprogramming erase the marks.
erase a mark	標識を消去する	Most marks are erased before fertilization.
after fertilization	受精後に	Reprogramming occurs shortly after fertilization.
wiped slate	白紙状態	Each generation begins with a wiped slate.
germ cell	生殖細胞	Marks are reset in developing germ cells.

❝例文

The marks are erased in two sweeping waves of reprogramming.
標識は二度の大規模な再プログラミングの波で消去される。
Each generation begins with a wiped slate.
各世代は白紙の状態から始まる。
Reprogramming occurs shortly after fertilization.
再プログラミングは受精直後に起こる。

💡Tip · 覚えるコツ

詳細問題は本文の具体表現を言い換えた選択肢を狙う。"two sweeping waves ... germ cells ... after fertilization" を正確に押さえれば、配列改変や不安定性などの偽の理由は排除できる。

問 3

What does the passage say about the rodent studies and exceptional loci it mentions?

The studies demonstrate that epigenetic effects vanish entirely within a single generation in all species.
The rodent studies provide conclusive proof that sequence-independent inheritance operates robustly in humans.
A few loci appear to escape erasure and some rodent studies report effects across two or three generations, but generalizing from these to humans remains speculative.
Every known genetic locus successfully evades the reprogramming waves in the rodents studied.

Phrase

A handful of loci appear to evade this scouring

1級読解詳細把握

⚡ひとことで

一部の遺伝子座と数件のげっ歯類研究は例外だが、ヒトへの一般化は推測の域とする。

選択肢の解説Choice Analysis

「A few loci appear to escape erasure and some rodent studies report effects across two or three generations, but generalizing from these to humans remains speculative.」

正解

本文は "A handful of loci appear to evade this scouring, and a few rodent studies report effects rippling across two or three generations" と例外を認めつつ、"extrapolating from such anomalies ... remains speculative" と続ける。例外の存在と、それをヒトに外挿することの不確かさが対で述べられている点が要点である。

「The rodent studies already provide conclusive proof that sequence-independent inheritance operates just as robustly in human populations as it does in mice.」
= ヒトでの配列非依存遺伝を決定的に証明 ━ 本文は anomalies からの外挿を "remains speculative" と明言し、確証を否定している。。
「Every known genetic locus successfully evades the reprogramming waves in the rodents studied.」
= あらゆる遺伝子座が再プログラミングを免れる ━ 回避するのは "a handful of loci"(一握り)のみで、全てではない。。
「The studies demonstrate that epigenetic effects vanish entirely within a single generation in all species.」
= 全種で一世代以内に効果が消える ━ 本文は二〜三世代に波及する効果を報告する研究に言及しており、全消失とは矛盾する。。

▦Collocation

パターン	意味	例
evade scouring	消去を免れる	A few loci evade the scouring of reprogramming.
ripple across generations	世代を越えて波及する	Effects ripple across two or three generations.
extrapolate from	〜から外挿する	It is risky to extrapolate from anomalies.
remain speculative	依然として推測的	Such conclusions remain speculative.
a handful of	ほんの一握りの	Only a handful of loci behave this way.

❝例文

A handful of loci appear to evade this scouring.
ほんの一握りの遺伝子座がこの消去を免れるようだ。
A few rodent studies report multigenerational effects.
数件のげっ歯類研究が複数世代にわたる効果を報告している。
Extrapolating to humans remains speculative.
ヒトへの外挿は依然として推測的である。

💡Tip · 覚えるコツ

例外を扱う設問では「例外を認める＋一般化は慎重」の両面を正確に映す選択肢が正解。"a handful" や "remains speculative" などの限定表現を見落とさないこと。

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EigoPro 1級 読解 — The Ghost in the Genome: Epigenetics and the Limits of Lamarck

この単元の問題を3問、解説つきで公開しています

Such enthusiasm outruns the evidence.

two sweeping waves of reprogramming

A handful of loci appear to evade this scouring

EigoPro 1級読解 — The Ghost in the Genome: Epigenetics and the Limits of Lamarck