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DNA Methylation: The Epigenetic Control System — Reading Comprehension

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This passage explores DNA methylation as an epigenetic mechanism that silences genes via methyl group tags. Covering roles in development (X-inactivation), disease (cancer), and environmental responses (diet/stress), it aligns with NGSS MS-LS3-1. Real-world examples include honeybee caste determination and human health impacts. Written for middle school life science, it simplifies complex concepts using analogies (molecular switches) and clear biological examples.

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"Epigenetic mechanisms" by National Institutes of Health / Wikimedia Commons.

DNA methylation is a crucial epigenetic mechanism that cells use to control gene activity without changing the underlying DNA sequence. By adding tiny chemical tags called methyl groups to DNA, this process acts like a molecular "off switch" that helps determine which genes are active or silent. Found in nearly all animals, plants, and fungi, DNA methylation plays essential roles in development, health, and disease.

How DNA Methylation Works

Chemical Tagging:

○ A methyl group (-CH₃) attaches to cytosine bases (usually where C is followed by G, called CpG sites).

○ This modification physically blocks proteins from reading the gene.

Gene Silencing:

○ Highly methylated genes are typically turned off.

○ Example: X-chromosome inactivation in female mammals relies on DNA methylation to silence one X chromosome.

Inheritance:

○ Some methylation patterns are copied during cell division.

○ Others are reset during reproduction or in response to environmental changes.

Biological Roles

● Development: Guides stem cells to become specialized (e.g., nerve vs. muscle cells).

● Genomic Stability: Silences harmful "jumping genes" (transposons).

● Disease: Abnormal methylation contributes to cancer (e.g., silencing tumor suppressor genes).

Environmental Influence

External factors can alter methylation patterns:

● Diet: Folate deficiency reduces methylation capacity.

● Stress: Childhood trauma leaves detectable methylation "scars."

● Toxins: Cigarette smoke changes methylation in lung cells.

Fun Fact: Honeybee larvae fed royal jelly develop into queens instead of workers—partly due to diet-induced DNA methylation changes!

What is DNA methylation?

A DNA mutationAdding methyl groups to DNABreaking DNA strandsCopying DNA

Where do methyl groups typically attach?

Adenine basesCpG sitesRibosomesCell membranes

How does methylation affect genes?

Makes them more activeSilences themCreates new genesDestroys DNA

What demonstrates methylation’s role in development?

X-chromosome inactivationPhotosynthesisBlood clottingMuscle contraction

Why is methylation important for health?

It prevents cancer when normalIt causes all diseasesIt only affects plantsIt makes DNA invisible

Which environmental factor alters methylation?

DietMoon phasesHair colorShoe size

What’s special about honeybee queens?

Diet changes their methylationThey lack DNAThey’re born as workersThey don’t use methylation

How is methylation inherited?

Some patterns copy during cell divisionIt’s always randomOnly from fathersIt can’t be inherited

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